The State-of The-art Report On Precast Concrete Pavements Pp-05-12.pdf

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State-of-the-Art Report on Precast Concrete Pavements

BLACK:

U.S. Department of Transportation Federal Highway Administration P P- 05- 12 First Editio n

U.S. Department of Transportation Federal Highway Administration

I n collab orat ion wit h

WHITE:

U.S. Department of Transportation Federal Highway Administration

Documents 1–4

U.S. Department of Transportation Federal Highway Administration

STATE-OF-THE ART REPORT ON PRECAST CONCRETE PAVEMENTS Includes Prestressed and other Precast Concrete Systems

Includes Documents One through Four

Publication PP-05-12

Precast/Prestressed Concrete Institute 200 West Adams Street, Suite 2100 Chicago, IL 60606-5230 Phone: 312-786-0300 Fax 312-621-1114 www.pci.org

PCI Publication PP-05-12 First Edition 2012 Copyright © 2012 By Precast/Prestressed Concrete Institute All rights reserved. No part of this book may be reproduced in any form without the written permission of the Precast/Prestressed Concrete Institute, except by a reviewer who wishes to quote brief passages in a review written for inclusion in a magazine or newsletter. ISBN 978-0-9853079-6-7

This document has been prepared and reviewed through an extensive Precast/Prestressed Concrete Institute (PCI) Committee process to present state-of-the-art information on precast concrete pavement systems. Substantial effort has been made to ensure that all collected data and information included in this report are accurate. PCI, the committee members, the authors, and the quoted agencies cannot accept responsibility for any errors or oversights in this report, the use of this material, or in the preparation of any design and engineering plans. This document is intended for reference by professional personnel who are competent to evaluate the significance and limitations of its contents and who are able to accept responsibility for the application of the material it contains. Actual conditions on any project must be given special consideration and more specific evaluation and engineering judgment may be required that are beyond the intended scope of this work. The contents do not necessarily reflect the official views or policies of the agencies mentioned, and do not constitute a standard or policy for design or construction.

Printed in the United States of America

FOREWORD This publication is the combination of four documents on the use of precast concrete pavement systems. They constitute a state-of-the-art report on this topic. The documents were developed through a cooperative agreement between the Precast/Prestressed Concrete Institute, PCI, and the Federal Highway Administration, FHWA. The individual documents are titled: Document One―Applications for Precast Concrete Pavements Document Two―Design and Maintenance of Precast Concrete Pavements Document Three―Manufacture of Precast Concrete Pavement Panels Document Four―Construction of Precast Concrete Pavements Each document will be of interest to a particular segment of the transportation industry but many will find this combined publication important for a complete understanding of the technology. While precast concrete pavements can be used for airfields, specialized intersections, and industrial applications, this report deals principally with highways. Precast concrete has been used for pavements to a limited extent over a relatively short period of time. The goal of this document is to share the experience to date and make suggestions about how precast concrete is best applied for this use. The suggestions are the consensus from a significant segment of stakeholders who have had this experience and those with expertise in precast concrete. Precast pavements have been shown to result in very rapid construction. This is important for use in areas that cannot tolerate extensive road closures or prolonged interference with traffic. It is expected that precast panels used for pavements will result in longer performance life due to high quality materials and proven practices used in industrial manufacturing facilities certified by PCI. Products are produced in compliance with stringent industry production and quality control standards. Many precast pavement panels are prestressed, maintaining compressive stresses in the concrete and greatly reducing cracks by design. Even before the first project was built in 2001, PCI recognized the potential of prefabricating pavements for the transportation industry and were active participants. Technical sessions with expert presentations were conducted at numerous PCI Annual Conventions. The PCI Transportation Activities Council recognized the need for a forum for practitioners throughout the industry including manufacturers and the owner agencies. In 2006, they facilitated the organization of the PCI Pavement Committee. The committee has been meeting in formal sessions at least twice each year since 2006. Under the provisions of the cooperative agreement with the FHWA, PCI has established a concise, yet comprehensive compilation of the body of knowledge about precast concrete pavements at the address www.precastconcretepavement.org on the world-wide web. The information at this site will be updated on a regular basis. PCI is recognized as the organization that develops and maintains the body of knowledge of the precast and precast, prestressed concrete industry. Since 1954, PCI has researched, refined, and published the technology of this industry. PCI developed comprehensive guidelines and standards for drafting, design, production, quality control, and installation of precast concrete. It administers the industry’s first and most comprehensive family of certification programs for personal, production, and erection of precast concrete―all of which are predicated on a continuous process of quality improvement. This publication adds to the body of knowledge for precast concrete, extending the applications of the material to the highway industry. PCI will continue to develop this technology and expand its coverage and detail to provide guidance to practitioners on the applications, design, fabrication, and construction of precast concrete pavements. Suggestions, questions, and comments concerning this document are welcome. Please contact Managing Director Transportation Systems at PCI; telephone 312-786-0300, or send your email to [email protected]

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DEVELOPMENT AND REVIEW Throughout the development of this publication, strict adherence to the PCI policies has been followed, including a series of reviews. The outline and each draft were reviewed by the Pavement Committee and its corresponding members who replied with written comments. These comments were generally discussed at the semi-annual meetings of the committee. The committee balloted the final draft and all written comments were accommodated through conference calls involving members of the committee. The document was given a comprehensive edit for style and PCI editorial standards and then submitted to the PCI Technical Activities Council (TAC) for assurance that it meets the Institute’s standards for technical content and quality guidelines for presentation. Primary comments resulting from the TAC ballot were resolved by the committee. It is planned that this publication will be revised and expanded as needed to keep abreast of research and industry practices and recommendations. All revisions will undergo a similar procedure for review and approval

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ACKNOWLEDGEMENTS This publication is a product of a cooperative agreement between PCI and the Federal Highway Administration. PCI wishes to thank FHWA for its participation, encouragement, and guidance in this work. In addition, other products will be developed as part of the cooperative agreement. The chairman of the PCI Pavement Committee, David K. Merritt, was instrumental in the accomplishment of this document. As a graduate student, Merritt worked under the direction of Drs. Ned H. Burns and Frank B. McCullough at the University of Texas at Austin on the development of design and construction methodologies for precast, prestressed concrete pavement. Their work culminated in the first such project in the United States in 2001 located in Texas. Merritt is a consultant to FHWA and has been uniquely involved in all the FHWA-state agency precast pavement demonstration projects throughout the country. With that experience, he first prepared the outline and then the first draft of this publication. Drawings and photographs not specifically otherwise identified have been provided courtesy of The Transtec Group, Inc. Over the several years of development, many others in addition to the committee engaged in discussions at the meetings and read one or more of the progression of drafts. PCI wishes to thank all of these professionals for their time and expertise. Many of those who participated in the PCI Pavement Committee process are acknowledged below. Special appreciation is extended to the following state agency persons who attended meetings and shared documents and experience from the precast concrete pavement projects in their states: Kirsten Stahl, California Department of Transportation William Stewart, Delaware Department of Transportation Karen Consiglio, Virginia Department of Transportation Claude Napier, Federal Highway Administration Daniel Hsiao, Utah Department of Transportation The following is a list of the active Voting Members of the PCI Pavement Committee at the time this document was printed David K. Merritt, Chair The Transtec Group, Inc.

R. Jon Grafton U.S. Concrete Precast Group / Pomeroy

Douglas M. Mooradian Precast/Prestressed Concrete Manufacturers Association of Calif

Frank W. Grubbs Grubbs Technical Services, Inc.

Theodore Neff Post-Tensioning Institute

Wallace Turner, Non-voting Precast/Prestressed Concrete Institute

Andy J. Keenan Prestress Engineering Company, LLC

Richard Potts Standard Concrete Products, Inc.

Reid W. Castrodale Carolina Stalite Company

Dan Kolb Prestress Engineering Company, LLC

William N. Nickas, Non-voting Precast/Prestressed Concrete Institute

John S. Dick J. Dick Precast Concrete Consultant, LLC

Larry Krauser General Technologies Inc.

Chuck Prussack Central Pre-Mix Prestress Co. Roy H. Reiterman Roy Reiterman, P.E. & Associates Ziad Sakkal Con-Fab California Corporation

Thomas R. Dodge Prestress Engineering Company, LLC

Donald F. Meinheit Wiss, Janney, Elstner Associates, Inc.

Peter Smith The Fort Miller Company, Inc.

Ken Fleck Insteel Wire Products

Tinu Mishra Caltrans - San Francisco Bay Region

Samuel S. Tyson Federal Highway Administration

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The following are Consulting Members of the PCI Pavement Committee. Consulting Members are not held to the same strict attendance standards for Voting Members as set forth in the PCI Group Operating Manual. Many of these members attended numerous meetings and participated in committee work including verbal and written reviews of the document. Heinrich O. Bonstedt Central Atlantic Bridge Associates

Mary Ellen Kimberlin Mary Ellen Kimberlin, LLC

Jack Schmerer RMS Productions

Ned H. Burns University of Texas at Austin, Retired

Steve Koch Sumiden Wire Products Corporation (SWPC)

Milenko Simic Prestressed Systems Inc.

John Dobbs Consultant

Bryan J. Lampe Dywidag Systems International USA, Inc.

D. Scott Eshleman Consultant Jim Fabinski EnCon Colorado Peter I. Finsen Georgia/Carolinas PCI Mukand V. Handa CSA International Joe Harrison General Technologies Inc. Simon Harton LEAP Associates International, Inc. Todd Hawkinson Wire Reinforcement Institute Timothy Holien Spancrete Mohsen A Issa University of Illinois at Chicago Venkatesh S. Iyer AMEC

Michael D. LaViolette HNTB Corporation Andrew Maybee Concrete Paving Association of Tennessee Thomas M. McEvoy Anil Mehta Prestressed Systems Inc. Ghulam Mujtaba Florida Department of Transportation Joseph L. Napoli American Spring Wire Celik Ozyildirim Virginia Transportation Research Center Burson Patton Texas Concrete Company Robert R. Roeller Dayton Superior Corporation

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Taylor Slate Hamilton Form Company Eric Steinberg Ohio University Shiraz Tayabji Fugro Consultants, Inc. Suneel N. Vanikar Federal Highway Administration Leif Wathne American Concrete Pavement Association Lee Wegner Hanson Structural Precast Eagle Richard Wells Insteel Wire Products Gary Wilson Concrete Technology Corporation Han-Ching Wu ConArt Precast LLC Alfred A. Yee Yee Precast Design Group Ltd. Paul Zia North Carolina State University, Retired

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INFORMATION FOR USERS

U1.0 ABOUT THIS DOCUMENT This publication is available as an electronic “eBook” and in hardcopy only after the eBook version has been obtained and registered. The electronic version is a secured PDF format that is particularly useful because it can be searched and contains links to other material. It is fully printable but cannot be moved to another user. PCI uses Adobe Digital Edition software that is the same tried and proven software used by the public library system for loaning books.

U1.1 STRUCTURE OF THE DOCUMENT U1.1.1 Using Links Links are provided from the Table of Contents to all numbered sections. The user may conveniently jump to a page number or to a section number. Links are provided to the websites of many of the cited references and to topics for additional information.

U1.1.2 Numbered Paragraphs Each main section in the text is identified with a decimal numbering system similar to the familiar system used for various AASHTO Specifications. This is the system that is used to organize this page you are reading. The hierarchy of the system is also apparent by the type size and font used in the title.

U1.1.3 Page Header The header on every page identifies the subject, the document number, and the title of the document.

U1.1.4 Page Footer The lower right corner shows the month and year of publication. In the center is the document number followed by a dash and the page number. Revised pages will show “a,” “b,” etc. following the page number and a new date in the right corner. This method will be useful to determine the most current revision.

U1.1.5 Figures and Tables All figures and tables are numbered to the section where they first appear. Example: Figure 3.2.-1 is found in Section 3.2 and Figure 3.2-2 is the second figure to appear in the same section. Figures and tables referenced in the text are in bold type.

U1.2 REVISIONS AND REGISTRATION Revisions to this document are expected. To receive revisions, or notices of revisions, it is required to register your copy of the Manual.

U1.2.1 Registering Your Copy There is no cost or obligation to register. Those obtaining an eBook through the PCI ePub website will be automatically registered to the email address registered with Adobe and the PCI ePub fulfillment system.

U1.2.2 Errors and Omissions Your help will be appreciated in locating errors and identifying omissions. Please contact PCI with your suggestions at [email protected].

U1.2.3 Dissemination of Corrections Corrections to this document when required will be assembled and a notice emailed to those registered. The replacement pages will readily identify the revision and the page will be identified as revised in the footer. vii

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Two methods are used to disseminate changes. Simple corrections, revisions, and improvements will be posted as “Errata” on the PCI Publications website, http://www.pci.org/cms/index.cfm/publications/errata. Or, select “Errata” on the Publications home page, then look for the title of this document. More complex revisions that involve more than a few pages may require the user to redownload the entire document. There will be no cost for this download. Instructions will be emailed as noted above. In the future, when a new edition is required, an email will notify registered users. There will likely be an additional charge for a new edition. Please keep your contact information current so you can be notified.

U1.3 EXCHANGE OF SUGGESTIONS U1.3.1 Send Your Suggestions Your suggestions and comments concerning this document will be greatly appreciated. Call, write or e-mail to “Bridge Engineer” at the location and telephone number on the inside cover page, or email [email protected].

U1.3.2 Our Suggestion We strongly urge the designer, in the early stages of a project, to contact one or more PCI-Certified precast concrete manufacturers. The manufacturer can advise about local experience and capability. The producer can often help with suggested solutions and cost estimates. They can provide specific design information about special local, state, or regional precast sections. A current list of PCI-Certified producers is readily available on the PCI website at www.pci.org.

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TABLE OF CONTENTS 1.0 INTRODUCTION ..........................................................................................................................................................................................1 - 1 1.1 CONSIDERATIONS FOR APPLICATION .............................................................................................................................................1 - 1 1.1.1 Needs for rapid construction ........................................................................................................................................................1 - 1 1.1.2 A Durable Solution ............................................................................................................................................................................1 - 1 1.1.3 Understanding Construction ........................................................................................................................................................1 - 1 1.1.4 Comparing PCPS with Existing Technology ...........................................................................................................................1 - 2 1.1.4.1Full-depth Precast Bridge Deck Panels ............................................................................................................................1 - 2 1.1.4.2 Cast-in-Place Prestressed Concrete Pavement ...........................................................................................................1 - 2 1.1.5 Benefits of Precast Construction .................................................................................................................................................1 - 2 1.1.5.1 Speed of Construction ............................................................................................................................................................1 - 3 1.1.5.2 Long-term Solution ..................................................................................................................................................................1 - 3 1.1.5.3 Durability .....................................................................................................................................................................................1 - 3 1.1.5.4 Quality-Assured Production ................................................................................................................................................1 - 3 1.1.5.5 Safety..............................................................................................................................................................................................1 - 3 1.1.5.6 Tolerance to Weather Conditions .....................................................................................................................................1 - 3 1.1.5.7 Sustainability ..............................................................................................................................................................................1 - 4 1.1.6 Cost Considerations ..........................................................................................................................................................................1 - 4 1.1.6.1 Initial Construction Cost........................................................................................................................................................1 - 4 1.1.6.2 Life-Cycle Cost............................................................................................................................................................................1 - 4 1.1.6.3 User Costs ....................................................................................................................................................................................1 - 4 1.1.6.4 Agency Costs ...............................................................................................................................................................................1 - 4 1.1.7 Survey of Jointed Precast Pavement Systems .......................................................................................................................1 - 4 1.1.7.1 Super Slab® .................................................................................................................................................................................1 - 5 1.1.7.2 Illinois Toll Highway Authority System..........................................................................................................................1 - 5 1.1.7.3 Kwik Slab® System ...................................................................................................................................................................1 - 5 1.1.7.4 Roman Road System ...............................................................................................................................................................1 - 6 1.1.7.5 Con-Slab® System .....................................................................................................................................................................1 - 6 1.1.7.6 Full-Depth Slab and Joint Replacement Method .........................................................................................................1 - 6 1.2 APPLICATIONS.............................................................................................................................................................................................1 - 6 1.2.1 New Construction ..............................................................................................................................................................................1 - 6 1.2.2 Reconstruction ....................................................................................................................................................................................1 - 7 1.2.2.1 Mainline ........................................................................................................................................................................................1 - 7 1.2.2.2 Ramps ............................................................................................................................................................................................1 - 8 1.2.2.3 Toll Lanes .....................................................................................................................................................................................1 - 8 1.2.3 Rehabilitation ......................................................................................................................................................................................1 - 9 1.2.3.1 Joint and Slab Replacement .................................................................................................................................................1 - 9 1.2.3.2 Unbonded Overlays .................................................................................................................................................................1 - 9 ix

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1.2.4 Bridge Approach Slabs ................................................................................................................................................................. 1 - 10 1.2.5 Airfield and Industrial Pavements .......................................................................................................................................... 1 - 11 1.2.6 Other Applications ......................................................................................................................................................................... 1 - 12 1.2.6.1 Widening ................................................................................................................................................................................... 1 - 12 1.2.6.2 Temporary Pavement.......................................................................................................................................................... 1 - 12 1.2.6.3 Weigh-in-Motion Sites ........................................................................................................................................................ 1 - 12 1.2.6.4 Intersections ............................................................................................................................................................................ 1 - 12 1.2.6.5 Limited Overhead Clearances .......................................................................................................................................... 1 - 12 1.3 CONSIDERATIONS FOR SITE SELECTION .................................................................................................................................... 1 - 12 1.3.1 Geometric Considerations .......................................................................................................................................................... 1 - 12 1.3.2 Existing Pavement Structure and Roadway ....................................................................................................................... 1 - 13 1.3.3 Utility Considerations ................................................................................................................................................................... 1 - 14 1.3.4 Jointed Precast Pavement Options.......................................................................................................................................... 1 - 14 1.4 AGENCY CONSIDERATIONS ................................................................................................................................................................ 1 - 14 1.4.1 Local Agencies .................................................................................................................................................................................. 1 - 14 1.4.2 Certified Precast Concrete Manufacturers .......................................................................................................................... 1 - 14 1.4.3 Agency Materials and Construction Specifications ......................................................................................................... 1 - 14 1.4.4 Lessons Learned ............................................................................................................................................................................. 1 - 15 1.4.4.1 Project Planning and Design ............................................................................................................................................ 1 - 15 1.4.4.2 Project Construction ............................................................................................................................................................ 1 - 16 1.5 RESOURCES FOR ADDITIONAL INFORMATION ........................................................................................................................ 1 - 16 1.6 CITED REFERENCES ............................................................................................................................................................................... 1 - 16 2.0 INTRODUCTION .......................................................................................................................................................................................... 2 - 1 2.1 FEATURES OF PPCP ................................................................................................................................................................................... 2 - 1 2.1.1 Types of PPCP Panels ....................................................................................................................................................................... 2 - 2 2.1.1.1 Typical Panels ............................................................................................................................................................................ 2 - 2 2.1.1.2 Specialized Panels .................................................................................................................................................................... 2 - 2 2.1.2 Cross Section Adaptability............................................................................................................................................................. 2 - 2 2.1.3 Prestressing ......................................................................................................................................................................................... 2 - 2 2.1.3.1 Pretensioning and Post-Tensioning ................................................................................................................................. 2 - 3 2.1.3.2 Two-Way Post-Tensioning ................................................................................................................................................... 2 - 4 2.1.3.3 Bonded Post-Tensioning ....................................................................................................................................................... 2 - 4 2.1.3.4 Unbonded Post-Tensioning ................................................................................................................................................. 2 - 5 2.1.3.5 Temporary Post-Tensioning ............................................................................................................................................... 2 - 5 2.1.4 Keyed Joints ......................................................................................................................................................................................... 2 - 6 2.1.4.1 Transverse Joints...................................................................................................................................................................... 2 - 6 2.1.4.2 Longitudinal Joints .................................................................................................................................................................. 2 - 7 2.2 DESIGN ............................................................................................................................................................................................................ 2 - 8 2.2.1 Geometric Considerations ............................................................................................................................................................. 2 - 8 x

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2.2.2 Panel Layout.........................................................................................................................................................................................2 - 8 2.2.3 Panel Thickness ..................................................................................................................................................................................2 - 8 2.2.4 Panel Plan Dimensions ....................................................................................................................................................................2 - 9 2.2.5 Connecting to Existing Structure ................................................................................................................................................2 - 9 2.2.6 Base Support ..................................................................................................................................................................................... 2 - 10 2.2.6.1 Level of Support ..................................................................................................................................................................... 2 - 10 2.2.6.2 Base and Subgrade Preparation...................................................................................................................................... 2 - 10 2.2.6.3 Friction-Reducing Layer ..................................................................................................................................................... 2 - 11 2.2.7 Nonprestressed Reinforcement ............................................................................................................................................... 2 - 12 2.2.8 Prestressing Requirements ........................................................................................................................................................ 2 - 12 2.2.8.1 Pretensioning .......................................................................................................................................................................... 2 - 13 2.2.8.2 Post-Tensioning ..................................................................................................................................................................... 2 - 13 2.2.9 Post-Tensioning Issues ................................................................................................................................................................ 2 - 13 2.2.9.1 Tendon Layout and Stressing Locations ..................................................................................................................... 2 - 13 2.2.9.2 Transverse Post-Tensioning............................................................................................................................................. 2 - 15 2.2.10 Corrosion Protection Strategy................................................................................................................................................ 2 - 15 2.2.10.1 Concrete Mix Design .......................................................................................................................................................... 2 - 15 2.2.10.2 Corrosion Protection ......................................................................................................................................................... 2 - 15 2.2.11 Expansion Joints ........................................................................................................................................................................... 2 - 16 2.2.11.1 Expansion Joint Requirements ..................................................................................................................................... 2 - 16 2.2.11.2 Type of Joints and Materials .......................................................................................................................................... 2 - 16 2.2.11.3 Joint Width ............................................................................................................................................................................. 2 - 17 2.2.12 Typical Panel Joints ..................................................................................................................................................................... 2 - 18 2.2.13 Functional Considerations ....................................................................................................................................................... 2 - 18 2.2.13.1 Skid Resistance .................................................................................................................................................................... 2 - 18 2.2.13.2 Ride Quality ........................................................................................................................................................................... 2 - 18 2.2.13.3 Tire-Pavement Noise......................................................................................................................................................... 2 - 18 2.2.13.4 Splash and Spray ................................................................................................................................................................. 2 - 19 2.3 PPCP MANAGEMENT CONSIDERATIONS ..................................................................................................................................... 2 - 19 2.3.1 Performance Monitoring ............................................................................................................................................................. 2 - 19 2.3.1.1 Pavement Performance ...................................................................................................................................................... 2 - 19 2.3.1.2 Instrumentation ..................................................................................................................................................................... 2 - 19 2.3.2 Routine Inspection and Maintenance .................................................................................................................................... 2 - 20 2.3.3 Potential Distress ............................................................................................................................................................................ 2 - 20 2.3.4 Recommendations Concerning Repair .................................................................................................................................. 2 - 22 2.3.5 Functional Maintenance .............................................................................................................................................................. 2 - 23 2.4 RESOURCES FOR ADDITIONAL INFORMATION ........................................................................................................................ 2 - 23 2.5 CITED REFERENCES ............................................................................................................................................................................... 2 - 24 3.0 INTRODUCTION ..........................................................................................................................................................................................3 - 1 xi

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3.1 INDUSTRY QUALITY ASSURANCE ...................................................................................................................................................... 3 - 1 3.1.1 Fundamentals of PCI Plant Certification ................................................................................................................................. 3 - 1 3.1.2 Quality Personnel Certification ................................................................................................................................................... 3 - 2 3.1.3 Qualified Fabricators ....................................................................................................................................................................... 3 - 2 3.1.4 The Plant Quality System Manual .............................................................................................................................................. 3 - 2 3.2 TOLERANCES................................................................................................................................................................................................ 3 - 2 3.2.1 Finished Product Tolerances ........................................................................................................................................................ 3 - 3 3.2.2 Tolerances for Reinforcement and Embedments ............................................................................................................... 3 - 5 3.2.3 Expansion Joints ................................................................................................................................................................................. 3 - 5 3.2.4 Formwork ............................................................................................................................................................................................. 3 - 6 3.3 MATERIALS ................................................................................................................................................................................................... 3 - 7 3.3.1 Concrete ................................................................................................................................................................................................. 3 - 7 3.3.1.1 Strength ........................................................................................................................................................................................ 3 - 7 3.3.1.2 Durability ..................................................................................................................................................................................... 3 - 7 3.3.1.3 Aggregates ................................................................................................................................................................................... 3 - 7 3.3.2 Prestressing Steel .............................................................................................................................................................................. 3 - 8 3.3.3 Nonprestressed Reinforcement .................................................................................................................................................. 3 - 8 3.3.4 Post-Tensioning Materials ............................................................................................................................................................. 3 - 8 3.3.4.1 Tendons ........................................................................................................................................................................................ 3 - 8 3.3.4.2 Ducts, Anchors, and Grout Ports ........................................................................................................................................ 3 - 9 3.3.5 Post-Tensioning Pockets ............................................................................................................................................................. 3 - 11 3.4 PRESTRESSING ......................................................................................................................................................................................... 3 - 12 3.4.1 Placement of Strands .................................................................................................................................................................... 3 - 12 3.4.2 Placement of Ducts and Anchors ............................................................................................................................................. 3 - 13 3.4.3 Transfer of Prestress ..................................................................................................................................................................... 3 - 14 3.5 EXPANSION JOINT PANELS ................................................................................................................................................................ 3 - 14 3.6 CONCRETE PLACEMENT, FINISHING, AND CURING ............................................................................................................... 3 - 15 3.6.1 Concrete Placement ....................................................................................................................................................................... 3 - 15 3.6.1.1 Protection of Embedments ............................................................................................................................................... 3 - 15 3.6.1.2 Consolidation .......................................................................................................................................................................... 3 - 16 3.6.2 Screeding, Finishing and Texturing ........................................................................................................................................ 3 - 17 3.6.3 Curing................................................................................................................................................................................................... 3 - 18 3.6.4 Procedures Following Fabrication .......................................................................................................................................... 3 - 19 3.7 PANEL NONCONFORMANCE .............................................................................................................................................................. 3 - 20 3.7.1 Nonconformance and Damage Assessment ........................................................................................................................ 3 - 20 3.7.1.1 Spalls ........................................................................................................................................................................................... 3 - 20 3.7.1.2 Cracks ......................................................................................................................................................................................... 3 - 22 3.7.1.3 Form Ridges on Keyways .................................................................................................................................................. 3 - 23 3.7.1.4 Dipping of Panel Edges ....................................................................................................................................................... 3 - 24 xii

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3.7.1.5 Corner Breaks ......................................................................................................................................................................... 3 - 24 3.7.1.6

Keyway Breaks ................................................................................................................................................................. 3 - 24

3.7.1.7

Surface Defects ................................................................................................................................................................. 3 - 25

3.7.2 Panel Repair Techniques ............................................................................................................................................................. 3 - 25 3.8 LIFTING AND HANDLING ..................................................................................................................................................................... 3 - 27 3.8.1 Lifting Devices .................................................................................................................................................................................. 3 - 27 3.8.2 Recommendations .......................................................................................................................................................................... 3 - 28 3.8.3 Storage and Shipping .................................................................................................................................................................... 3 - 29 3.9 ACCEPTANCE TESTING AT FABRICATION PLANT................................................................................................................... 3 - 31 3.9.1 Panel Fit-Up ....................................................................................................................................................................................... 3 - 31 3.9.2 Duct Inspection ................................................................................................................................................................................ 3 - 31 3.10 FABRICATION OF JOINTED PRECAST PAVEMENT PANELS ............................................................................................. 3 - 32 3.10.1 Uniqueness of JPPS ...................................................................................................................................................................... 3 - 32 3.10.2 Quality Assurance ........................................................................................................................................................................ 3 - 32 3.10.2.1 Pre- and Post-pour Inspection ...................................................................................................................................... 3 - 32 3.10.2.2 Tolerances .............................................................................................................................................................................. 3 - 32 3.10.3 Formwork ........................................................................................................................................................................................ 3 - 33 3.10.4 Materials .......................................................................................................................................................................................... 3 - 35 3.10.4.1 Concrete .................................................................................................................................................................................. 3 - 35 3.10.4.2 Tie Bars and Threaded Dowel Bar Splice Couplers ............................................................................................. 3 - 35 3.10.4.3 Dowels ..................................................................................................................................................................................... 3 - 35 3.10.4.4 Dowel Bond Breaker ......................................................................................................................................................... 3 - 36 3.10.4.5 Lifting Devices ...................................................................................................................................................................... 3 - 36 3.10.5 Concrete Placement, Finishing, and Curing ...................................................................................................................... 3 - 36 3.10.6 Finishing Procedures after Fabrication ............................................................................................................................. 3 - 36 3.10.7 Storage and Shipping .................................................................................................................................................................. 3 - 36 3.11 RESOURCES FOR ADDITIONAL INFORMATION ..................................................................................................................... 3 - 36 3.12 CITED REFERENCES ............................................................................................................................................................................ 3 - 37 4.0 INTRODUCTION ..........................................................................................................................................................................................4 - 1 4.1 INSTALLATION STAGING AND SEQUENCING ...............................................................................................................................4 - 1 4.1.1 Type of Project ....................................................................................................................................................................................4 - 1 4.1.2 Construction Windows ....................................................................................................................................................................4 - 2 4.2 BASE PREPARATION .................................................................................................................................................................................4 - 2 4.2.1 Equipment Requirements ..............................................................................................................................................................4 - 3 4.2.2 Types of Bases .....................................................................................................................................................................................4 - 3 4.2.3 Tolerance of Base Surface ..............................................................................................................................................................4 - 5 4.2.4 Grouting Voids under Panels ........................................................................................................................................................4 - 5 4.2.5 Friction-Reducing Membrane ......................................................................................................................................................4 - 6 4.3 CONSTRUCTION MATERIALS ...............................................................................................................................................................4 - 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4.3.1 Post-Tensioning Tendons .............................................................................................................................................................. 4 - 6 4.3.2 Joint Epoxy............................................................................................................................................................................................ 4 - 7 4.3.3 Tendon and Under-slab Grouts ................................................................................................................................................... 4 - 8 4.3.4 Expansion Joint Seals ....................................................................................................................................................................... 4 - 8 4.3.5 Materials to Fill Holes and Pockets ............................................................................................................................................ 4 - 9 4.4 PANEL INSTALLATION ......................................................................................................................................................................... 4 - 11 4.4.1 Trial Installation.............................................................................................................................................................................. 4 - 11 4.4.2 Equipment and Mobilization ..................................................................................................................................................... 4 - 11 4.4.3 Panel Alignment .............................................................................................................................................................................. 4 - 13 4.4.3.1 Horizontal Alignment .......................................................................................................................................................... 4 - 13 4.4.3.2 Vertical Alignment ................................................................................................................................................................ 4 - 13 4.4.4 Panel Joints ........................................................................................................................................................................................ 4 - 13 4.4.5 Temporary Post-Tensioning ...................................................................................................................................................... 4 - 14 4.4.6 Mid-Slab Anchor .............................................................................................................................................................................. 4 - 15 4.4.7 Under-slab Grouting ...................................................................................................................................................................... 4 - 16 4.4.8 Filling Holes and Pockets ............................................................................................................................................................ 4 - 17 4.4.9 Other Considerations .................................................................................................................................................................... 4 - 17 4.4.9.1 Intermittent Traffic and Transition Slabs .................................................................................................................. 4 - 17 4.4.9.2 Incremental Changes in Pavement Length ................................................................................................................ 4 - 18 4.5 POST-TENSIONING PROCEDURES ................................................................................................................................................... 4 - 18 4.5.1 Equipment and Mobilization ..................................................................................................................................................... 4 - 19 4.5.2 Tendon Installation ....................................................................................................................................................................... 4 - 19 4.5.3 Stressing Final Tendons .............................................................................................................................................................. 4 - 20 4.5.4 Grouting Ducts ................................................................................................................................................................................. 4 - 22 4.6 REPAIRS AND SURFACE REMEDIATION ...................................................................................................................................... 4 - 23 4.6.1 Diamond Grinding .......................................................................................................................................................................... 4 - 23 4.6.2 Damage Assessment ...................................................................................................................................................................... 4 - 23 4.6.2.1 Spalls ........................................................................................................................................................................................... 4 - 24 4.6.2.2 Cracks ......................................................................................................................................................................................... 4 - 25 4.6.2.3 Corner and Keyway Breaks .............................................................................................................................................. 4 - 26 4.6.3 Repair Techniques ......................................................................................................................................................................... 4 - 26 4.7 FINAL INSPECTION ................................................................................................................................................................................ 4 - 28 4.7.1 Responsibility for Inspection .................................................................................................................................................... 4 - 28 4.7.2 Key Inspection Items..................................................................................................................................................................... 4 - 28 4.7.3 Optional Inspection and Documentation ............................................................................................................................. 4 - 28 4.8 RESOURCES FOR ADDITIONAL INFORMATION ........................................................................................................................ 4 - 28 4.9 CITED REFERENCES ............................................................................................................................................................................... 4 - 29

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LIST OF FIGURES Figure 1.1.3-1 Identification of Components of PPCP ........................................................................................................................1 - 2 Figure 1.1.7-1 Components of Jointed Precast Pavement Systems..............................................................................................1 - 5 Figure 1.2.1-1 PPCP Installations for New Construction ..................................................................................................................1 - 7 a) Project near Georgetown, Tex. ...........................................................................................................................................................1 - 7 b) Project in Indonesia ...............................................................................................................................................................................1 - 7 Figure 1.2.2.1-1 Mainline Pavement Reconstruction Projects Using PCPS During Nighttime Closures ....................1 - 8 a) PCPS Used in Virginia ............................................................................................................................................................................1 - 8 b) PCPS Used in Delaware .........................................................................................................................................................................1 - 8 Figure 1.2.2.2-1. Ramp Reconstruction During Nighttime Closures in Virginia ...................................................................1 - 8 a) A slab from the Existing Ramp Being Removed .........................................................................................................................1 - 8 b) A New Jointed Precast Pavement Slab Being Installed ...........................................................................................................1 - 8 Figure 1.2.3.1-1 Replacing Deteriorated Pavement Joints with Nonprestressed Precast Panels .................................1 - 9 a) In Michigan Using the Full-depth Slab and Joint Replacement method ..........................................................................1 - 9 b) In New Jersey Using the Super Slab® System .............................................................................................................................1 - 9 Figure 1.2.3.2-1. Unbonded Concrete Overlay Concept (Graphic: Harrington, 2008) .................................................... 1 - 10 Figure 1.2.4-1. PCPS used for Bridge Approaches in Iowa .......................................................................................................... 1 - 11 a) Two Panels Formed the Width of the Approach Roadway ................................................................................................ 1 - 11 b) Panels after Installation and Grouting ........................................................................................................................................ 1 - 11 Figure 1.2.5-1. PPCP Panels can be used for a Variety of Applications .................................................................................. 1 - 11 a) Heavy-Use Industrial Application in Alaska ............................................................................................................................. 1 - 11 b) Precast Airfield Pavement in New York ..................................................................................................................................... 1 - 11 Figure 1.3.1-1 Roadway Curvature is not a Limitation for PPCP .............................................................................................. 1 - 13 a) Customized, Curved, Prestressed, Heavy-Use Industrial Pavement Panels .............................................................. 1 - 13 b) Typical PPCP Panels Used in a Vertical Curve in Texas ....................................................................................................... 1 - 13 Figure 2.1-1 Identification of Components and features of PPCP ................................................................................................2 - 1 Figure 2.1.2-1 Pavement Cross Sections that can be Achieved with Precast Concrete Panels ........................................2 - 2 a) Uniform Cross-Slope ..............................................................................................................................................................................2 - 2 b) Crowned Cross-Slope―Single Panel ...............................................................................................................................................2 - 2 c) Asymmetric Cross-Slope―Single Panel ..........................................................................................................................................2 - 2 d) Crowned Cross-Slope―Two Panels .................................................................................................................................................2 - 2 Figure 2.1.3.1-1 Formwork and Reinforcement for PPCP Panels. Pretensioning is Longitudinal in the Form (Transverse to Traffic Direction) and Post-tensioning is Across the Form (Longitudinal to Traffic and the Pavement) .............................................................................................................................................................................................................2 - 4 Figure 2.1.3.5-1 Temporary Post-tensioning used to Clamp Panels Together During Installation ..............................2 - 6 a) Tensioning Strand Tendons ................................................................................................................................................................2 - 6 b) Tensioning Threaded Bar Tendons .................................................................................................................................................2 - 6 Figure 2.1.4.1-1 Tongue and Groove Panel Keyway ...........................................................................................................................2 - 7 xv

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a) Typical Keyway Dimensions............................................................................................................................................................... 2 - 7 b) Keyway Joint Shown in Installed Panels ....................................................................................................................................... 2 - 7 Figure 2.1.4.1-1 Longitudinal Panel Joint ................................................................................................................................................ 2 - 7 a) Facing Female Keyways in a Longitudinal Joint ........................................................................................................................ 2 - 7 b) Joint Filled with Grout and Finished ............................................................................................................................................... 2 - 7 Figure 2.2.3-1 Multiple "Levels" of Reinforcement to Consider when Determining Thickness of Panels. ................ 2 - 9 Figure 2.2.5-1 Options for Connecting Precast Pavement to Existing Pavement at Terminal Ends using a Closure Placement (Left) or Dowel/Tie-Bar Slots (Right). ............................................................................................................................ 2 - 10 Figure 2.2.6.2-1 Base materials used for PPCP .................................................................................................................................. 2 - 11 a) Dense-Graded Asphalt Concrete .................................................................................................................................................... 2 - 11 b) Permeable Asphalt Treated Base .................................................................................................................................................. 2 - 11 c) Lean Concrete ......................................................................................................................................................................................... 2 - 11 d) Crushed Stone ........................................................................................................................................................................................ 2 - 11 e) Pervious Concrete ................................................................................................................................................................................ 2 - 12 f) Granular Base .......................................................................................................................................................................................... 2 - 12 Figure 2.2.6.3-1 Friction-Reducing Membranes................................................................................................................................ 2 - 12 a) 6-Mil Polyethylene Sheeting ............................................................................................................................................................ 2 - 12 b) Geotextile Fabric ................................................................................................................................................................................... 2 - 12 Figure 2.2.9.1-1 Stressing Techniques used for PPCP .................................................................................................................... 2 - 14 a) Central Stressing ................................................................................................................................................................................... 2 - 14 b) End Stressing.......................................................................................................................................................................................... 2 - 14 Figure 2.2.11.2-1 Types of PPCP Expansion Joints........................................................................................................................... 2 - 17 a) Armored Joint Before Placement in Form ................................................................................................................................. 2 - 17 b) Armored Joint in Service ................................................................................................................................................................... 2 - 17 c) Plain Dowelled Joint with Elastomeric Seal .............................................................................................................................. 2 - 17 d) Header-Type Joint with Silicone Seal .......................................................................................................................................... 2 - 17 Figure 2.3.3-1 Examples of Possible Distresses in PPCP ............................................................................................................... 2 - 21 a) Transverse Panel Crack ..................................................................................................................................................................... 2 - 21 b) Spall at Panel Joint ............................................................................................................................................................................... 2 - 21 c) Expansion Joint Seal Deterioration ............................................................................................................................................... 2 - 21 d) Cracking Around Perimeter of Stressing Pockets .................................................................................................................. 2 - 21 e) Lifting Anchor Patch Deterioration .............................................................................................................................................. 2 - 22 Figure 3.2.1-1 Definition of Dimensional Tolerances ........................................................................................................................ 3 - 4 Figure 3.2.4-1 Heavy-duty Steel Formwork used for PPCP Panel Fabrication ....................................................................... 3 - 7 Figure 3.3.4.2-1 Post-tensioning Duct Materials ............................................................................................................................... 3 - 10 a) Galvanized Metal Spiral Duct .......................................................................................................................................................... 3 - 10 b) Both Plastic and Galvanized Metal Ducts .................................................................................................................................. 3 - 10 c) Rigid Plastic Single-Strand Duct ..................................................................................................................................................... 3 - 10 Figure 3.3.4.2-2 Examples of Post-Tensioning End Anchorage Assemblies ......................................................................... 3 - 10 xvi

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a) Fully Encapsulated Anchor............................................................................................................................................................... 3 - 10 b) Manufactured Anchor ......................................................................................................................................................................... 3 - 10 c) Two-strand Anchorage ....................................................................................................................................................................... 3 - 11 d) Spring-loaded Encapsulated Anchor ........................................................................................................................................... 3 - 11 Figure 3.3.4.2-3 Mid-panel Grout Vents used with Plastic Ducts ............................................................................................... 3 - 11 a) Ribbed Plastic Duct .............................................................................................................................................................................. 3 - 11 b) Smooth Plastic Duct ............................................................................................................................................................................ 3 - 11 Figure 3.3.5-1 Types of Forms used for Stressing Pockets ........................................................................................................... 3 - 12 a) Steel Form Wrapped with Thin Layer of Foam ....................................................................................................................... 3 - 12 b) One-time-use Wood Form ................................................................................................................................................................ 3 - 12 c) Steel forms with Drafted Sides and Lids to Prevent Filling during Concrete Placement ..................................... 3 - 12 Figure 3.4.1-1 The Trajectory of Prestressing Strands may be Deviated in the Forms ................................................... 3 - 13 a) Steel Bulkheads between Panels used to Deflect Pretensioning Strands ................................................................... 3 - 13 b) Steel Chairs used to Support Pretensioning Strands at Deflection Points ................................................................. 3 - 13 Figure 3.4.2-1 Post-tensioning Ducts must be Held Rigidly in Place in the Forms ............................................................ 3 - 13 a) Plastic Ducts Supported with Multiple Chairs ........................................................................................................................ 3 - 13 b) Rigid Metal Ducts Supported between Pretensioning Strands ....................................................................................... 3 - 13 Figure 3.5-1 Fabricating Expansion Joint Panels .............................................................................................................................. 3 - 15 a) Armored Expansion Joint .................................................................................................................................................................. 3 - 15 b) First of Two Halves of a Header-type Joint ............................................................................................................................... 3 - 15 c) Second Half of a Plain Dowelled Joint Set Up to Cast ............................................................................................................ 3 - 15 Figure 3.6.1.1-1 Fabrication and Concrete Placement Techniques .......................................................................................... 3 - 16 a) Internal Vibrators being used to Consolidate Concrete around Well-anchored Blockout Formers ............... 3 - 16 b) The Second Lift of Concrete is shown being Placed in a Two-lift Production Sequence ...................................... 3 - 16 Figure 3.6.1.2-1 PPCP Panels Fabricated for Two Projects with Variable Thickness ....................................................... 3 - 16 Figure 3.6.2-1 Panel Surface Textures ................................................................................................................................................... 3 - 17 a) A Section of Artificial Turf is being Drug to Impart a Longitudinal Finish .................................................................. 3 - 17 b) A Specially Fabricated Bristle Broom the Full Width of the Panel Applies a Longitudinal Finish ................... 3 - 17 c) A Jig with Tines was used to Apply a Longitudinal Finish .................................................................................................. 3 - 18 d) Applying a Transverse Broom Texture ...................................................................................................................................... 3 - 18 Figure 3.6.3-1 Concrete Curing Techniques ........................................................................................................................................ 3 - 19 a) Ambient Curing using Curing Compound) ................................................................................................................................ 3 - 19 b) Steam Applied under Plastic Tarpaulins .................................................................................................................................... 3 - 19 c) Dry Heat Applied under Curing Cover (being lowered) ...................................................................................................... 3 - 19 d) Supplemental Wet Mat Curing after Stripping ........................................................................................................................ 3 - 19 Figure 3.7.1.1-1 Examples of Fabrication-Related Spalling ......................................................................................................... 3 - 21 a) Surface Spall (crack filled with epoxy) ........................................................................................................................................ 3 - 21 b) Keyway Spall (bottom lip of keyway) ......................................................................................................................................... 3 - 21 c) Edge Spall (above pretensioning strand) ................................................................................................................................... 3 - 21 xvii

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d) Blockout Spall ........................................................................................................................................................................................ 3 - 21 e) Grout Port Spall ..................................................................................................................................................................................... 3 - 22 Figure 3.7.1.2-1 Examples of Fabrication-Related Cracks ............................................................................................................ 3 - 23 a) Surface Crack .......................................................................................................................................................................................... 3 - 23 b) Surface Crack due to Shrinkage ..................................................................................................................................................... 3 - 23 c) Keyway Crack ......................................................................................................................................................................................... 3 - 23 Figure 3.7.1.3-1 A Ridge in the Keyway Surfaces due to a Form Joint..................................................................................... 3 - 24 Figure 3.7.1.5-1 Cracks Visible Indicating a Broken Corner ........................................................................................................ 3 - 24 Figure 3.7.1.6-1 Extensive Keyway Damage ....................................................................................................................................... 3 - 25 Figure 3.7.1.7-1 Finished Surface Defects ............................................................................................................................................ 3 - 25 a) Surface Scaling ....................................................................................................................................................................................... 3 - 25 b) Aggregates Dislodged during Finishing ..................................................................................................................................... 3 - 25 Figure 3.7.2-1 Examples of Panel Repairs in Progress ................................................................................................................... 3 - 26 a) Spalled Keyway Repair (Spalled Area Saw Cut and Removed) ........................................................................................ 3 - 26 b) Spalled Blockout Repair (Spalled Area Saw Cut and Removed) ..................................................................................... 3 - 26 c) Surface Crack Filled with Epoxy by Gravity .............................................................................................................................. 3 - 27 Figure 3.8.1-1 The Impact to the Surface of various Lifting Devices used in PPCP Panels ............................................ 3 - 28 a) A Type of “Quick Connect” Anchor Pocket Showing Headed Lifting Stud ................................................................... 3 - 28 b) Another Type of “Quick Connect” Pocket with Lifting Anchor Shown ......................................................................... 3 - 28 c) Simple Recessed Threaded Coil Lifting Insert ......................................................................................................................... 3 - 28 Figure 3.8.2-1 The use of Strongbacks and Spreader Beams for Handling Panels ............................................................ 3 - 29 a) Strongback Bolted to the top of a Joint Panel .......................................................................................................................... 3 - 29 b) Strongback Mounted to the End of a Joint Panel .................................................................................................................... 3 - 29 c) Spreader Beam used with a Wheeled Travel Lift to keep Lift Lines Vertical ............................................................. 3 - 29 d) Spreader Beam used with a Fork Lift for Handling Panels ................................................................................................ 3 - 29 Figure 3.8.3-1 Panel Configurations for Storage and Shipping................................................................................................... 3 - 30 a) Storage of Panels with Variable Thickness ............................................................................................................................... 3 - 30 b) Storage of Panels with Uniform Thickness ............................................................................................................................... 3 - 30 c) Shipment of a Single Panel of Width Greater than 8 Ft ...................................................................................................... 3 - 30 d) Shipment of Multiple Panels ........................................................................................................................................................... 3 - 30 Figure 3.9.1-1 PPCP Panel Fit-up Tests at the Fabrication Plant prior to Full-Scale Production ................................ 3 - 31 Figure 3.10.3-2 Isometric View of a Warped Precast Panel ......................................................................................................... 3 - 34 Figure 3.10.3-3 Cross-sectional Views of Warped Precast Panels ............................................................................................ 3 - 34 Figure 3.10.3-4 Proprietary Casting Table and Forming System for Warped Precast Panels ...................................... 3 - 35 Figure 4.2.2-1 Base Materials that have been used for PPCP ......................................................................................................... 4 - 4 a) Dense Graded Asphalt Concrete ....................................................................................................................................................... 4 - 4 b) Permeable Asphalt Treated Base ..................................................................................................................................................... 4 - 4 c) Lean Portland Cement Concrete ....................................................................................................................................................... 4 - 4 d) Crushed Stone ........................................................................................................................................................................................... 4 - 4 xviii

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e) Pervious Portland Cement Concrete ...............................................................................................................................................4 - 5 f) Fine Graded Aggregate ...........................................................................................................................................................................4 - 5 Figure 4.2.5-1 Friction-reducing Membranes between the Base and the Panel ....................................................................4 - 6 a) Polyethylene Sheet ..................................................................................................................................................................................4 - 6 b) Geotextile Fabric ......................................................................................................................................................................................4 - 6 Figure 4.3.1-1 Coated and Uncoated Prestressing Strands .............................................................................................................4 - 7 a) Seven-wire Prestressing Strands from the Top: Uncoated; Smooth Epoxy-Coated; Fine Grit-Impregnated Epoxy-Coated; Coarse Grit-Impregnated Epoxy-Coated .............................................................................................................4 - 7 b) Close-up of Cross Section of Epoxy-Coated and Epoxy-filled Strand ...............................................................................4 - 7 Figure 4.3.2-1 Epoxy Application to Keyways during Panel Installation ..................................................................................4 - 8 a) Application of Joint Epoxy with Cloth.............................................................................................................................................4 - 8 b) Epoxy Applied to both Faces; Post-tensioning Strands are seen between Panels Prior to Moving Them Together. Note Epoxy kept away from Ducts. ..................................................................................................................................4 - 8 Figure 4.3.4-1 Expansion Joint Seals..........................................................................................................................................................4 - 9 a) Preformed Elastomeric Seal ...............................................................................................................................................................4 - 9 b) Preformed Closed Cell Seal .................................................................................................................................................................4 - 9 c) Poured Silicone Seal with Header Material ..................................................................................................................................4 - 9 Figure 4.3.5-1 Pea Gravel Concrete Mixture (left) and Rapid Setting Concrete Mixture (right) Shown being used to Fill Stressing Pockets. .................................................................................................................................................................................... 4 - 10 a) Pea Gravel Concrete Mixture ........................................................................................................................................................... 4 - 10 b) Rapid Setting Concrete Mixture ..................................................................................................................................................... 4 - 10 Figure 4.3.5-2 Cold Patch Asphalt Shown used to temporarily Fill Stressing Pockets for Rapid Opening to Traffic 4 10 Figure4.4.1-1 A Trial Installation is Shown being Conducted near the Project Site using the Same Personnel, Equipment, Procedures, and Materials as Planned for the Project. .......................................................................................... 4 - 11 Figure 4.4.2-1 Examples of Equipment used to install Pavement Panels .............................................................................. 4 - 12 a) All-terrain Crane ................................................................................................................................................................................... 4 - 12 b) Crawler Crane ........................................................................................................................................................................................ 4 - 12 c) Mobile Crane ........................................................................................................................................................................................... 4 - 12 d) Front End Loader ................................................................................................................................................................................. 4 - 12 Figure 4.4.4-1 Panel Joint Considerations ............................................................................................................................................ 4 - 14 a) Epoxy Squeezed from the Top of the Joint ................................................................................................................................ 4 - 14 b) Compressible Foam Gaskets Adhered around each Duct (Both Panels) ..................................................................... 4 - 14 Figure 4.4.5-1 Tensioning Temporary Post-tensioning Tendons .............................................................................................. 4 - 15 a) Temporary Strand Tendons............................................................................................................................................................. 4 - 15 b) Temporary Bar Tendons ................................................................................................................................................................... 4 - 15 Figure 4.4.6-1 Mid-slab Anchors .............................................................................................................................................................. 4 - 16 a) Anchor Bar Drilled, Driven, and to be Grouted into Central Stressing Pocket .......................................................... 4 - 16 b) Anchor Bars Installed in Sleeves Cast into Panels ................................................................................................................. 4 - 16 Figure 4.4.7-1 Two Under-slab Grouting Techniques used for PPCP ...................................................................................... 4 - 17 xix

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a) Under-slab Grouting by Gravity Feed .......................................................................................................................................... 4 - 17 b) Under-slab Grouting by Low-Pressure Injection ................................................................................................................... 4 - 17 Figure 4.4.9.1-1 Temporary Precast Panel used to Fill the Gap between the End of the Precast Pavement and the Existing Pavement. ......................................................................................................................................................................................... 4 - 18 Figure 4.5.3-1 Central Stressing ............................................................................................................................................................... 4 - 20 a) Splicing Two Lengths of Tendon at a Central Stressing Panel using a Dogbone Anchor ..................................... 4 - 20 b) Close-up of Dogbone Anchor in a Central Stressing Panel................................................................................................. 4 - 20 Figure 4.5.3-2 Examples of End Stressing from Pockets in the Joint Panels. ....................................................................... 4 - 21 Figure 4.5.3-3 Transverse Post-tensioning ......................................................................................................................................... 4 - 21 a) Installing Transverse Post-tensioning Strands ....................................................................................................................... 4 - 21 b) Tensioning Transverse Strands ..................................................................................................................................................... 4 - 21 Figure 4.5.4-1 Grouting Post-tensioning Ducts ................................................................................................................................. 4 - 22 a) Duct Grout Tube Extensions on the Surface of the Panels ................................................................................................. 4 - 22 b) Flush Grout Vents Ready to Accept Tube Extensions .......................................................................................................... 4 - 22 Figure 4.6.1-1 Diamond Grinding used to Ensure Compliance with Ride Quality Specifications ............................... 4 - 23 a) Diamond Grinding in Progress Across a Panel Joint ............................................................................................................. 4 - 23 b) A Full Blanket Grind of a Concrete Pavement Surface ......................................................................................................... 4 - 23 Figure 4.6.2.1-1 Examples of Spalling that may occur during Construction. ....................................................................... 4 - 24 a) Mid-Panel Joint Spall (Note: Spalled Area Prior to Diamond Grinding on Right, and After Diamond Grinding on Left) ........................................................................................................................................................................................................... 4 - 24 b) Corner Spall ............................................................................................................................................................................................ 4 - 24 c) Lifting Anchor Patch Spall (Note: the Edges and Perimeter of Anchor Patch Material have Spalled) ............ 4 - 24 d) Spalled Corner Patch (Note: Corner had been Patched Prior to Panel Installation; Patch Spalled after Posttensioning) .................................................................................................................................................................................................... 4 - 24 Figure 4.6.2.2-1 Examples of Panel Cracks that may occur during Construction. ............................................................. 4 - 25 a) Keyway Crack ......................................................................................................................................................................................... 4 - 25 b) Mid-Panel Transverse Crack ........................................................................................................................................................... 4 - 25 c) Shrinkage Crack around Perimeter of Filled Stressing Pocket......................................................................................... 4 - 26 d) Shrinkage Crack Around Perimeter of Filled Lifting Anchor ............................................................................................ 4 - 26 Figure 4.6.2.3-1 Examples of Keyway and Corner Breaks that may occur during Construction ................................ 4 - 26 a) Broken Keyway ..................................................................................................................................................................................... 4 - 26 b) Corner Break .......................................................................................................................................................................................... 4 - 26 Figure 4.6.3-1 Examples of Keyway Repairs to Panels Damaged during Construction................................................... 4 - 27 a) Damaged Area Saw Cut and Cleaned for Patching ................................................................................................................. 4 - 27 b) Repaired Keyway Prior to Diamond Grinding......................................................................................................................... 4 - 27

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LIST OF TABLES Table 3.2.1-1 Dimensional Tolerances .....................................................................................................................................................3 - 5 Table 3.2.2-1 Tolerances for Reinforcement and Embedments ....................................................................................................3 - 5 Table 3.2.3-1 Tolerances for Expansion Joints ......................................................................................................................................3 - 6 Table 3.10.2.2-1 Tolerances for Jointed Precast Pavement Panels ........................................................................................... 3 - 32

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PRECAST, PRESTRESSED CONCRETE PAVEMENTS_________________________________________________DOCUMENT ONE

APPLICATIONS FOR PRECAST CONCRETE PAVEMENTS 1.0 Introduction/1.1 Considerations for Application

1.0 INTRODUCTION This first of four documents on the use of precast concrete pavement systems (PCPS), provides guidance for owner agencies for determining appropriate applications. It describes the benefits of PCPS to the traveling public realized through reduced traffic disruption due to 1) speed of construction, 2) improved durability, 3) improved safety, 4) and all-weather construction. The many types of applications that are appropriate for precast concrete pavements are described. There are also brief descriptions of some projects that have been completed. In defining terminology, when PCPS are prestressed, either pretensioning in the fabrication plant, or posttensioned during construction, they are referred to as precast, prestressed concrete pavement or PPCP. Nonprestressed precast concrete panels are called jointed precast pavement systems, or JPPS.

1.1 CONSIDERATIONS FOR APPLICATION As a new technology, the costs and benefits of using PCPS for a project must be weighed carefully. Although comparable in cost to certain rapid-setting cast-in-place concrete pavement systems, PCPS at present may not be cost-competitive with traditional cast-in-place concrete paving or hot-mix asphalt pavement. Therefore, the benefits of rapid construction, durability, and long-term performance must be evaluated against alternatives. These benefits can be quantified as life-cycle costs (i.e., costs over the life of the pavement) in terms of reduced costs for pavement maintenance and rehabilitation, as well as the user inconvenience costs during construction and during any future maintenance and rehabilitation activities.

1.1.1 Needs for rapid construction There is a strong and growing demand in the United States for rapid construction techniques. This is due to:    

Aging and rapidly deteriorating pavement infrastructure Heavier trucks A large and increasing percentage of truck traffic More vehicles and greater congestion

The most common applications for PCPS are for reconstruction or rehabilitation in urban areas. In these areas, lane closures are generally restricted to only one or two lanes at a time, and are permitted only during short windows of opportunity. PCPS provide a paving technique well suited to isolated overnight or weekend construction periods. The pavement can be opened to traffic almost immediately after the precast panels are installed because the panels are usually prestressed, adequately supported, and have reached their design compressive strength in the fabrication plant.

1.1.2 A Durable Solution The primary consideration when comparing PCPS to other rapid construction techniques, such as rapid-setting concrete and hot-mix asphalt, is the life expectancy, or durability and longevity, of precast pavement. PCPS are designed to be a long-term solution and not a temporary or short-term fix. Other materials that are less expensive for immediate repairs will likely exhibit much shorter useful pavement life. It is expected that precast pavement, particularly if prestressed (PPCP), will be a low-maintenance solution.

1.1.3 Understanding Construction The construction of PPCP involves the installation of prefabricated concrete panels on a prepared base. The panels themselves provide the final riding surface of the finished pavement and do not require an overlay. They are typically used to replace existing pavement but can also be used for new construction or even to overlay existing pavement. Precast concrete panels are generally provided large enough to match the width of one, two, or three lanes of the existing pavement, permitting one or multiple lanes to be reconstructed at one time, depending on site access and clearance constraints. The longest dimension of the precast panels is commonly oriented perpendicular to the roadway centerline. The panel may include one or both shoulders. In general, the panels are pretensioned in the longer direction during fabrication, and during construction, are post-tensioned together in groups longitudinally, 1-1

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PRECAST, PRESTRESSED CONCRETE PAVEMENTS_________________________________________________DOCUMENT ONE

APPLICATIONS FOR PRECAST CONCRETE PAVEMENTS 1.1 Considerations for Application

in the direction of traffic, to act as continuous slabs. It is important that prestress is provided in both directions if the maximum benefits of prestressing are to be realized. Figure 1.1.3-1 shows a schematic view of typical PPCP. Some of the key components of this system will be discussed further in this and the other three documents in this series. Figure 1.1.3-1 Identification of Components of PPCP Mid-Slab Anchor Panels/Mid-Slab Anchor Sleeves (End Stressing Configuration)

Joint Panel

Central Stressing Panels/P-T Stressing Pockets (Central Stressing Configuration) Base Panels P-T Stressing/Anchor Access Pockets Expansion Joint Prepared Base

Joint Panel

Transverse Pretensioning

Post-Tensioning Bar Tendon (Optional)

Friction-Reducing Membrane Longitudinal Post-Tensioning Strand Tendons

Longitudinal Post-Tensioning Ducts

Keyway Panel Joints

1.1.4 Comparing PCPS with Existing Technology 1.1.4.1Full-depth Precast Bridge Deck Panels PPCP is significantly different from conventional cast-in-place concrete paving. However, it is similar to precast concrete panels long used for highway and railway bridges. Full-depth and partial-depth concrete bridge deck panels, precast concrete box girder segments, and various kinds of precast, prestressed concrete deck girders are all used in bridge construction. There are obvious differences, such as the support conditions, design requirements, and load-carrying capacity. Yet many of the basic methods, such as prefabrication procedures, pretensioning, post-tensioning, field grouting, and joint treatments are similar to this existing technology. The State-of-the-Art Report on Full-Depth Precast Concrete Bridge Deck Panels (PCI, 2011), provides a useful reference for many details that are similar to precast concrete pavement panels. 1.1.4.2 Cast-in-Place Prestressed Concrete Pavement Many techniques used for PPCP have evolved from technology used in the past for cast-in-place (CIP), prestressed concrete pavements (PCP). While prestressed concrete pavement technology has had limited use in the United States, several PCP projects constructed in the 1970s are still in service today and provide evidence of the durability and performance advantages of prestressing in pavements (Tayabji et al., 2001, Medina-Chavez and Won, 2006). The lessons learned from those projects constructed more than 40 years ago have been applied to PPCP.

1.1.5 Benefits of Precast Construction PCPS have many benefits for owner agencies and the general public compared to other methods. Precast concrete transfers a time-consuming stage of construction to a factory and away from traffic. Forming, placing, and curing the concrete is moved to a climate- and quality-controlled manufacturing environment. A precast concrete 1-2

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APPLICATIONS FOR PRECAST CONCRETE PAVEMENTS 1.1 Considerations for Application

pavement can be opened to traffic almost immediately after the panels are installed. These benefits and methods are described in the sections that follow. Factory precasting allows the advantages of prestressing to be realized. Prestressing precompresses the concrete and results in greater structural capacity and improved durability. PPCP can allow thinner panels to be used and provides improved durability by greatly reducing or eliminating cracking. 1.1.5.1 Speed of Construction The primary advantage of precast pavement technology is the potential for rapid construction, or more importantly, faster opening of the pavement to traffic by eliminating on-site curing. While cast-in-place concrete can be placed at a faster rate than setting precast panels, curing time is required before the pavement is subjected to traffic. Even rapid-setting concrete paving mixtures require a minimum of 2 to 4 hours for curing. In a short closure period, that reduces the time available for construction activities. 1.1.5.2 Long-term Solution PCPS are designed to be a long-term solution. Projections are for a 30- to 40-year service life. If a shorter lifespan is adequate (e.g., for isolated repairs of a highway that will be completely reconstructed in a short period of time), other techniques may be more cost effective. However, if long-term performance is important, PCPS promises an attractive alternative. 1.1.5.3 Durability Precast concrete lends itself to durable solutions. This results from concrete materials, mixtures, and methods that are used in permanent precast concrete manufacturing plants. Furthermore, concrete mixtures are transported only a short distance between the batch plant and the forms, helping to ensure mixture uniformity. Precast plants offer many options for curing concrete. Some provide indoor fabrication, heat-assisted curing, and even wet mat curing after removal from the forms. These are some of the options available to help ensure improved durability of the finished product. In-situ concrete shrinkage is largely eliminated as most shrinkage will occur prior to installation during curing and storage of the panels at the fabrication plant. Pretensioning in the plant improves durability by greatly reducing or eliminating cracking. The concrete is precompressed from the time it is removed from the forms through the life of the pavement. 1.1.5.4 Quality-Assured Production In order to ensure the highest level of quality and durability, the panels should be manufactured in a precast plant actively participating in the PCI Plant Certification Program. In this program, independent auditing engineers conduct multiple unannounced inspections each year. Plants are graded and lose their certification if they do not meet industry standards for production and quality control. All plants must compile a comprehensive Quality Standards Manual (QSM). This manual must detail all the necessary steps to ensure that products meet customer expectations. The QSM must include the manufacturing and quality control (QC) procedures necessary to produce the precast pavement panels. Much more information about PCI Plant Certification is available from PCI at www.pci.org, select “Quality Systems and the BOK (Body of Knowledge).” 1.1.5.5 Safety Safety in the work zone is an important advantage of precast pavement. By permitting construction to be completed during short closures, it can be restricted to non-peak travel times when both worker exposure to traffic and traffic exposure to construction operations and traffic control measures is minimized. 1.1.5.6 Tolerance to Weather Conditions Precast pavement allows construction through a wider range of weather conditions. While conventional CIP concrete construction is generally restricted by ambient temperatures (e.g., 95 °F and falling or 34 °F and rising), and cannot be placed during periods of heavy or prolonged rainfall, PCPS can be installed in most weather conditions, assuming those conditions do not affect other factors such as the condition of the supporting base and delivery of the panels. While certain components of the PPCP system, such as epoxies or grouts, may be sensitive to weather conditions, there are generally options for these components that will allow their use in inclement weather conditions. 1-3

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1.1.5.7 Sustainability PCPS are recognized to be a sustainable solution. Sustainability concepts include the impacts of construction on the traveling public and the longevity of the construction. PCPS are fast to install, thereby reducing traffic congestion and the associated pollution during construction. Precast concrete products are designed for long life, prolonging the life cycle of construction, and reducing waste and energy consumption (Merritt and Tyson, 2011).

1.1.6 Cost Considerations First costs are traditionally the most heavily weighted factors in determining how a highway project will be built. For a rapid construction, long-life solution such as PCPS, other costs must be factored into decision making. These include life-cycle, user, and other agency costs. 1.1.6.1 Initial Construction Cost Initial construction costs (“first costs”) are the costs of actually building a project, and primarily include the payments made to the contractor(s). Less tangible, but still significant, are the costs to the agency for inspection and any acceptance testing that must be completed. Another significant component of the first cost is the cost for maintenance of traffic (MOT) during construction. For projects restricted to construction during overnight or weekend closures, MOT can be substantial as it must be mobilized and disassembled each construction period, and generally requires additional safety measures, such as crash attenuator vehicles. Many state highway agencies now evaluate MOT costs in their evaluation of project bids through “A + B” bidding, where “A” is the actual construction cost (materials, labor, etc.), and “B” is a “lane rental” cost based on the number of days or hours of lane closure required to complete the project. When a project includes lane rental, any additional pavement a contractor can construct in a work shift will contribute to a lower lane rental factor for the project. 1.1.6.2 Life-Cycle Cost Life-cycle cost (LCC) is the total estimated cost of a pavement over its useful life, and includes both initial construction cost and the costs of projected maintenance, operation, and rehabilitation over its entire life. Many LCC analyses also consider user costs, discussed below, as well as salvage value or disposal cost at the end of the useful life of the pavement. When the life-cycle cost is considered in estimating the equivalent cost of alternatives, anticipated future maintenance and rehabilitation costs (including associated user cost and final salvage value) are converted to present worth to account for inflation of costs in the future. Therefore, a pavement which may have higher initial costs but lower long-term maintenance and rehabilitation costs may actually be more economical than a pavement with lower initial costs and higher maintenance and rehabilitation costs. 1.1.6.3 User Costs User costs are those costs that are borne by the traveling public that are attributable to the pavement. User costs include user inconvenience costs created during construction and future maintenance and rehabilitation, which are generally quantified in terms of lost work time, increased fuel consumption, and increased pollution, among others. There are other user costs that are real, but more difficult to quantify, such as increased vehicle maintenance due to pavement in poor condition. Pavements that can be constructed and maintained with minimal disruption to the travelling public, and will maintain an increased level of service or functional performance over its life result in greatly reduced total user costs. 1.1.6.4 Agency Costs Similar to user costs, agency costs can be difficult to quantify for a project, but can nevertheless be a significant consideration. Anticipated agency costs for newer technology such as PCPS, would include training costs for inspectors, and possibly increased testing costs for materials used that are not common to conventional pavement construction. Inspection costs for nighttime or weekend construction may also be higher than conventional construction due to overtime pay for employees and testing labs. On the other hand, some agencies favor the concept of plant-cast concrete pavement because quality assurance associated with manufacturing good quality concrete may cost less and be more cost effective if it is done in the plant rather than in the field.

1.1.7 Survey of Jointed Precast Pavement Systems For some projects, more than one precast pavement system may be required in order to accommodate site conditions. Several jointed precast pavement systems (JPPS) have been developed and provide the same benefit 1-4

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of rapid construction as PPCP. Figure 1.1.7-1 shows some of the key components of various jointed precast pavement systems currently available. Nonprestressed, precast concrete pavement systems offer a unique advantage: individual precast panels can be removed if necessary and replaced without concern for maintaining the integrity of continuous post-tensioning tendons as in a prestressed pavement. This may be beneficial, for example, in pavements in urban areas where utility cuts are expected. Nonprestressed pavement systems also provide a solution that is more easily adapted to complex intersections and challenging geometries such as superelevated sections, compound curves, or applications with unusual features like drainage inlets and manholes. Prestressed JPPS have also been developed and utilize two-way pretensioning in lieu of a double mat of mild steel reinforcement. Similar to nonprestressed JPPS, they can be used for isolated slab replacements, providing the additional benefit of prestressed pavement. Figure 1.1.7-1 Components of Jointed Precast Pavement Systems Ports for Underslab Grout or Foam Injection

Reinforced Precast Concrete Panels

12 ft – 20 ft Joint Spacing

Ports for Grouting Dowel Bar Slots (Bottom of Slab Configuration)

Dowel Bars (in wheelpaths only or across full width)

Underslab Grout or Polyurethane Foam

Dowel Bar Slots (Bottom of Slab Configuration)

Dowel Bar Slots (Top of Slab Configuration)

1.1.7.1 Super Slab® The Super-Slab system (http://www.super-slab.com/),developed by the Fort Miller Co., Inc., of Schuylerville, N.Y., is a jointed, heavily reinforced, precast concrete pavement system that essentially replicates (in terms of slab thickness and joint spacing) a conventional CIP jointed pavement. Super-Slab is a slab-on-grade system used for highways, ramps, and for airport pavement replacement. The system is also used effectively for approach slabs to bridges and tunnels, for crosswalks, and complex urban intersections. Super-Slab panels are cast to exacting tolerances and placed on carefully pregraded subbase surfaces that have tolerances similar to those of the panels. Panels interlock with adjacent panels through load-transfer dowels and mating slots cast into the bottom of the panels, as shown in Figure 1.1.7-1. To ensure complete slab support, special grout is pumped into a network of grout distribution channels in the bottom surface of the slabs effectively filling voids that may exist between the slabs and subbase. Both planar and warped panels are available. The Super-Slab system can accommodate virtually any roadway geometry. 1.1.7.2 Illinois Toll Highway Authority System A joint contractor-agency committee in Illinois developed standard plans for a jointed, nonprestressed, precast concrete pavement system. It uses dowel bars for load transfer and mating slots that are either cast or saw cut onsite into the top of the panels, as shown in Error! Reference source not found.. This system has been used rimarily for intermittent, spot repair applications. 1.1.7.3 Kwik Slab® System A slightly different proprietary precast concrete pavement system, named Kwik Slab (http://www.kwikslab.com/), utilizes patented KWIK JOINT® reinforcing bar couplers to provide continuously 1-5

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reinforced pavements for roadways, airfields, and bridge decks. High strength grout is used in the panel joints and reinforcing bar couplers. 1.1.7.4 Roman Road System The Roman Road System (http://www.romanstoneco.com/pavement-slab.html) was developed by Roman Stone Construction Company of Bayshore, N. Y. The system utilizes reinforced concrete panels and a dowelled load transfer system with mating slots that are saw-cut into the top of the panels on site during construction (Error! eference source not found.). This system is used primarily for intermittent repairs of existing concrete pavement. One of the primary differences between this system and other jointed systems is the use of expansive polyurethane foam pumped beneath the panels to fill voids and lift them to the proper elevation as the foam expands. 1.1.7.5 Con-Slab® System The Con-Slab precast pavement system (Mishra et al., 2011) was developed by Con-Fab California Corporation in Lathrop, Calif. The system uses two-way pretensioning in the precast panels. Either a post-tensioned or dowelled load transfer system is utilized to connect the precast panels. The dowelled version of the system can be used for smaller isolated slab repairs. The precast panels are installed on a prepared base at the proper elevation and grout is pumped beneath the panels to fill any voids. 1.1.7.6 Full-Depth Slab and Joint Replacement Method An FHWA-sponsored research project conducted by Michigan State University from 2003-2006 led to the development of a method for using precast concrete panels for full-depth slab replacements and joint reconstruction (Buch, 2001). This non-proprietary method uses reinforced precast panels to replace deteriorated jointed concrete pavement slabs or deteriorated joints between pavement slabs. Slots are saw-cut into the existing pavement to receive dowels that are cast into the precast panels. The slots are grouted after the precast panel is in place, providing load transfer between the existing pavement and precast panel.

1.2 APPLICATIONS 1.2.1 New Construction PCPS are most cost-effective for reconstruction and rehabilitation of existing pavements, but also have applications for new construction. There are sections of highway construction projects that require rapid construction. This would include locations where access must be provided to construction vehicles or detoured traffic. The rate of construction for PCPS will probably not be competitive with conventional cast-in-place (slipform) paving for new construction of mainline pavement. However, there may be portions of a project where PCPS could be used. These include bridge approach slabs or intersections with intersecting highways or streets. Other opportunities include by-pass lanes around toll booths to facilitate electronic tolling. Such lanes are being installed in many states and need to be installed quickly with as little disruption to traffic as possible. Other mainline applications for PPCP include projects in remote areas without convenient access to ready-mix concrete or specialized paving equipment. The first PPCP project in the United States is shown in Figure 1.2.1-1a. It was constructed in 2001 as a demonstration project to provide 1,100 ft of I-35 frontage road near Georgetown, Tex. (Merritt et al., 2002). The largest such project to date was a mainline pavement completed in 2009 in Indonesia on the Island of Java shown in Figure 1.2.1-1b (Nantung et al., 2010). The new 22-mile-long alignment of four-lane divided highway utilized PPCP . The primary value of using PPCP was to avoid importing large specialty paving equipment, and to boost the local economy through the employment of hundreds of local workers for precasting and construction.

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Figure 1.2.1-1 PPCP Installations for New Construction

a) Project near Georgetown, Tex. (Photo: Merritt et al., 2002)

b) Project in Indonesia (Photo: Tommy Nantung)

1.2.2 Reconstruction The vast majority of highway infrastructure work in the United States involves reconstruction of existing facilities that have reached the end of their useful lives. Most of this infrastructure renewal is occurring in urban areas where lane closures must be minimized. Reconstruction means the complete removal of a pavement section with a new pavement. Reconstruction may or may not include the removal and reconstruction of the underlying base and subgrade. For most rapid-renewal applications, it is desirable to minimize disruption or replacement of the underlying material. An advantage of PPCP for reconstruction is that it has the potential to eliminate the need for replacement of underlying base layers. PPCP can be designed to account for less than optimum support by adjusting the level of reinforcement or prestress in the panels. The use of precast pavement also permits reconstruction to be completed in shorter lane closures, one section at a time, keeping the pavement open to traffic during peak travel times. 1.2.2.1 Mainline Mainline pavement reconstruction often has a major impact on the travelling public as many highways, particularly in urban areas, already exceed their designed capacity, especially during peak travel times. Closing even a single lane for reconstruction can substantially increase congestion and associated travel delays. For this reason, many state highway agencies consider only one of the following options as a viable solution for mainline reconstruction in urban areas: 

Full closure of the roadway for the duration of construction, with available detour routes clearly identified to the traveling public.



Closure of only one or two lanes at a time, and only during non-peak travel times (generally nighttime or weekend closures).

Full closures of a roadway will permit conventional cast-in-place paving operations. Nightly or weekend closures of one or two lanes will require rapid-construction techniques such as PCPS. PCPS will not only meet the requirements for rapid reconstruction, but will provide a longer-lasting pavement. The Virginia and Delaware Departments of Transportation installed PPCP using nighttime closures. These projects are shown in Figure 1.2.2.1-1 (see Merritt and Tyson, 2011).

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Figure 1.2.2.1-1 Mainline Pavement Reconstruction Projects Using PCPS During Nighttime Closures

a) PCPS Used in Virginia (Photo: David Shiells, Virginia Department of Transportation)

b) PCPS Used in Delaware

1.2.2.2 Ramps Ramps are the critical links to every highway. The closure of ramps for reconstruction can result in long detours to adjacent ramps which can significantly increase congestion and impact safety. Minimizing the closure time of ramps for reconstruction is a very important consideration, and PPCP offers a solution that will permit ramp reconstruction to be completed during non-peak travel times. Ramps were part of the project constructed in Virginia as reported in Merritt and Tyson (2011), and shown in Figure 1.2.2.2-1. Figure 1.2.2.2-1. Ramp Reconstruction During Nighttime Closures in Virginia

a) A slab from the Existing Ramp Being Removed

b) A New Jointed Precast Pavement Slab Being Installed

1.2.2.3 Toll Lanes Maintaining traffic flow on toll lanes and through toll plazas is crucial for sustaining revenue flow. Therefore, it is important to minimize closure of these lanes for rehabilitation and reconstruction of the pavement. Precast pavement offers a solution that can be limited to times of non-peak toll lane usage when construction will not adversely affect traffic flow.

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1.2.3 Rehabilitation Rehabilitation is a treatment applied to an existing pavement that will help prolong its useful life at a lower cost than full reconstruction. For concrete pavements, overlays and repairs to, or replacement of, individual slabs or sections of slabs are common rehabilitation techniques. These are further described in the following sections. 1.2.3.1 Joint and Slab Replacement Common repairs to concrete pavements, where precast panels can be used, involve joint and slab replacements. For joint replacements, a 2 to 4 ft section of the pavement slab on both sides of a joint is saw-cut the full depth of the slab and removed. This area can then be replaced with a precast panel, with dowel bars providing load transfer between the existing pavement and the new panel. Slab replacements involve a similar process except that an entire pavement slab (between joints) or multiple consecutive slabs, are saw-cut and removed, and replaced by a precast panel, or multiple precast panels. Dowels are used to provide load transfer between the existing pavement and precast panels. Reinforced JPPS are most commonly used for this application, but prestressed JPPS have also been used. The products described in Section 1.1.7 are ideally suited for these replacements. The Full-Depth Slab and Joint Replacement Method developed in Michigan and Super Slab by the Fort Miller Company are shown in Figure 1.2.3.1-1. The photos are taken from and the projects described in Buch (2007) and Tayabji et al. (2011). Figure 1.2.3.1-1 Replacing Deteriorated Pavement Joints with Nonprestressed Precast Panels

a) In Michigan Using the Full-depth Slab and Joint Replacement method

b) In New Jersey Using the Super Slab® System

1.2.3.2 Unbonded Overlays An unbonded overlay is a concrete pavement constructed over the top of an existing concrete pavement with a thin layer used to break the bond between them, as shown in Figure 1.2.3.2-1. The bond breaker is usually hotmix asphalt or non-woven geotextile. Unbonded overlays provide an efficient solution for rehabilitation of an existing concrete pavement that has reached its service life. Leaving the existing pavement in place eliminates the need for demolition and disposal and provides a substantial base for the new pavement. See Harrington (2008), for more information. Unbonded PCPS overlays permit the existing pavement to remain in service as the overlay pavement is constructed. Temporary transitions are provided at the ends of the new overlay to transition traffic from the existing pavement onto the new PCPS and back to the existing pavement. Temporary precast panels can be used for these transitions and reused throughout the project. Prestress levels in the PPCP can be adjusted as necessary to account for the level of support from the underlying pavement, and to allow the overlay to be as thin as possible.

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Full-width panels are an ideal application for overlays. While lane-by-lane construction is also possible, it would require additional maintenance of traffic considerations. Constructing an unbonded overlay one lane at a time with PCPS would require safety barriers between lanes to protect traffic from the drop-off between the new overlay in one lane and existing pavement in the adjacent lane. Figure 1.2.3.2-1. Unbonded Concrete Overlay Concept (Graphic: Harrington, 2008)

1.2.4 Bridge Approach Slabs Bridge approach slabs provide a transition from pavement slab on grade to the bridge deck. Loss of support from erosion or incomplete compaction of fill material behind the abutments can cause approach slabs to settle (and eventually fail), leading to the well-known “bump at the end of the bridge.” Ideally, problems with the fill material should be addressed through construction practices, but PPCP provides an excellent solution for rapid reconstruction of failed approach slabs during short closures. Further, PPCP approach slabs can be designed for flexural strength to act as a transition slab-bridge should voids form beneath the approach slab in the future. PPCP approach slabs can also provide a solution for new construction. The approach slabs can be installed immediately after the bridge and embankment are constructed. This allows the paving train to pave directly up to the approach slab and stop, travel across the bridge, and continue paving, rather than having to be moved around the bridge as is the case when special approach slabs need to be formed and concrete placed between the bridge deck and the end of the continuous paving section. Precast approach slabs have been used on a large number of accelerated bridge construction projects throughout the United States. Well documented projects were conducted in Iowa shown in Figure 1.2.4-1 and described in Dunn et al. (2007).

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Figure 1.2.4-1. PCPS used for Bridge Approaches in Iowa

a) Two Panels Formed the Width of the Approach Roadway

b) Panels after Installation and Grouting

1.2.5 Airfield and Industrial Pavements PCPS have been used for airfield pavements to a limited degree in the United States. In general, precast concrete pavement has been used for critical areas, such as aprons, taxiways, and runways at busy airports that cannot be closed to aircraft except during short overnight windows. Precast concrete panels have been used previously for temporary pavement at the intersection of two runways. This allowed operations on one runway during conventional reconstruction of the other. Airfield pavement slabs are generally much thicker than conventional highway pavements, and individual slabs are generally much larger in size. This may require the use of multiple precast concrete panels to replace a single existing slab. Prestress levels can be adjusted so that thinner panels can be used, while also providing for higher flexural handling stresses from larger panel sizes. Similar to airfield pavements, industrial pavements and driveways may support very heavy wheel loads, requiring stronger pavement sections. Usually, they cannot be closed for long periods of time for reconstruction. PPCP provides a solution for heavy-duty pavement where the prestress levels in the panels can be adjusted for the load levels that the pavement will experience. This provides a solution for pavements at ports, container yards, mines, warehouses, and other facilities where construction must be completed during very short closures. Applications are shown in Figure 1.2.5-1 and described in Merritt et al. (2008). Figure 1.2.5-1. PPCP Panels can be used for a Variety of Applications

a) Heavy-Use Industrial Application in Alaska (Photo: Teck Alaska Incorporated)

b) Precast Airfield Pavement in New York (Photo: Shiraz Tayabji) 1 - 11

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1.2.6 Other Applications A variety of other specific potential applications for PCPS include: widening, temporary pavement, weigh-inmotion sites, intersections, and pavement sections with limited overhead clearance. These are described in the following sections. 1.2.6.1 Widening Widening an existing pavement typically involves removal of the existing shoulder and replacement with structural pavement and new shoulder. In general, the pavement structure beneath the existing shoulder is not designed for mainline traffic loading, which could require significant base and subgrade reconditioning. PCPS offer a solution for widening an existing pavement that can be installed during short closures while providing the new required structural capacity. 1.2.6.2 Temporary Pavement PCPS provide a solution for temporary pavements. Construction of crossovers and detours can be a very costly component of a pavement reconstruction project. PPCP panels can be used for the crossovers and can potentially be re-used multiple times. Post-tensioning would link the panels together. The tendons would simply need to be removed prior to relocating the panels. Although this application has not been used for highway pavements to date, precast panels have been used for runway intersections at airfields, as previously discussed. 1.2.6.3 Weigh-in-Motion Sites Weigh-in-motion (WIM) sensors are commonly installed in concrete pavements, which are resistant to temperature and plastic deformation effects. Using precast concrete pavement, the WIM sensors, or a recess to receive the sensors, can be cast into a panel for rapid installation during a short closure of the pavement. If the existing pavement is asphalt, an entire section (500 ft or more) of the existing pavement can be removed and replaced with precast concrete pavement (including a panel with the WIM sensors) during a short closure of the roadway. 1.2.6.4 Intersections Intersections are unique in that they affect travel for two roadways. Intersections can generally be closed only for very short periods of time. PCPS provide a rapid construction solution for this type of application. Most intersections are three-dimensional in nature, with combinations of various cross-slopes and grade changes. This requires a detailed survey of the intersection including locating all utilities prior to designing the layout of the precast panels. 1.2.6.5 Limited Overhead Clearances For reconstruction of pavements beneath bridges or other structures with limited clearance, PPCP provides a solution that can reduce the thickness of the pavement section, while resulting in desirable short-term lane closures. High-strength concrete in combination with prestressing can result is pavement thicknesses significantly less than traditional pavements.

1.3 CONSIDERATIONS FOR SITE SELECTION Site selection will have a significant effect on the cost and overall viability of using PCPS. This section describes considerations for determining whether a project may be suitable for PCPS.

1.3.1 Geometric Considerations Horizontal and vertical curvature and superelevated sections present challenges for PPCP design and construction. Because the panels are post-tensioned together, their dimensions are critical for ensuring that the assembled pavement follows the designed alignment. Pavement sections with only vertical curvature (see Fig. 1.3.1-1) can be accommodated with standard PPCP panels and details. Superelevated or horizontally curved roadway sections, however, will require a detailed survey of the roadway and the corresponding fabrication of panels, where each panel is unique and must be placed in a predefined location. This does not necessarily require match-casting of the precast concrete panels, but match-casting may be a preferred solution for certain applications with very complex geometries. Production of special precast concrete panels, particularly if they are match-cast, will increase the cost of the panels and require additional time for production. 1 - 12

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Crowned pavement sections can be accommodated by varying the thickness of full-width precast panels or by using panels of uniform thickness and creating a continuous longitudinal joint at the crown line. Sections with variable cross slopes, such as superelevation transition areas, can be accommodated with special proprietary warped or folded panels of uniform thickness or by varying the thickness of each panel to accommodate the varying surface geometry. If uniform thickness panels are not used in these areas, the thickness of panels may need to be varied within each panel and from panel to panel complicating panel fabrication and subgrade preparation requirements. Figure 1.3.1-1 Roadway Curvature is not a Limitation for PPCP

a) Customized, Curved, Prestressed, Heavy-Use Industrial Pavement Panels (Photo: Teck Alaska Incorporated)

b) Typical PPCP Panels Used in a Vertical Curve in Texas (Photo: Merritt et al., 2002)

1.3.2 Existing Pavement Structure and Roadway The existing pavement or roadway may introduce challenges in the layout and design of PPCP. The result may be to simply create unique panels to accommodate the special conditions. Field issues may include matching the elevation of an existing adjacent section of pavement, matching the cross-slope of adjacent existing pavement, placing precast panels between two existing pavement sections, or accommodating drainage inlets, manholes, or other utility constraints. Matching the elevation or cross-slope of an adjacent section of pavement is difficult because of the inherent variability in cast-in-place concrete construction. Profile and grade information provided to the contractor (or collected by the contractor) will be required for proper design and layout of the panels prior to construction. Placing panels between two existing pavement sections (e.g., replacing the middle lane of a three-lane pavement) is challenging due to the likelihood of variable widths of the existing lane. A detailed survey of the existing pavement will permit the panels to be fabricated to fit between the adjacent lanes, but will likely require unique panels to fit in specific locations. Construction of PCPS in areas with drainage inlets, manholes, utility covers, etc., will present challenges for designing and fabricating the panels to accommodate the fixture. In general, the panels must be fabricated with slightly “oversized” block-outs so there will be some tolerance for slight misalignment when the panel is installed. The gap between the panel and utility fixture can then be filled with a flexible material that can accommodate movement of the pavement slab. 1 - 13

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For all unique applications such as these, it may be necessary to develop shop drawings based on digital terrain models of the existing roadway. Then, the precast concrete panels can be produced to fit each unique location.

1.3.3 Utility Considerations Underground utilities should be carefully considered when determining what PCPS to use, recognizing the pavement may need to be removed for maintenance purposes. The designer, using PPCP in these areas, must consider that the precast panels are individually pretensioned and linked together with post-tensioning tendons. Cutting through the pavement slab can result in a loss of prestress near the area that is removed, and restoring prestress may be very difficult unless the system is designed to account for this. If there is a potential for future utility cuts in the pavement, the PPCP should be designed so the post-tensioning system can be detensioned for removal of individual precast panels and later reassembled and re-tensioned. Unbonded post-tensioning tendons (strands or bars) provide a solution; however, there has not been any experience in using unbonded post-tensioning for PPCP applications to date. Construction details and practices may need to be altered to accommodate unbonded post-tensioning. Alternatively, for unexpected utility cuts, it may also be possible to remove an individual panel and replace it with a single pretensioned panel, which is connected to the remaining pavement with dowels.

1.3.4 Jointed Precast Pavement Options The considerations for site selection discussed in the preceding parts of Section 1.3, may necessitate the use of other precast pavement systems, such as JPPS that are better able to accommodate complex geometries, existing pavement constraints, and the removal of individual panels for utility maintenance. A combination of more than one precast pavement system may provide the best solution. JPPS described in Section 1.1.7, provide alternative solutions for addressing specific site constraints, while PPCP can be used for areas without such constraints. JPPS have been constructed to accommodate large superelevations with proprietary warped precast panels, and have also been used for intersections and pavements with numerous intrusions (drainage inlets, manholes, etc.). JPPS can also be saw-cut and removed without concern for compromising post-tensioning tendons.

1.4 AGENCY CONSIDERATIONS 1.4.1 Local Agencies PCPS may provide a viable solution for city and county agencies for the repair or reconstruction of intersections and arterial streets. PCPS are not intended only for large-scale highway or urban applications. However, local agencies may not be familiar or have experience with precast concrete construction. Expertise may be available from the state highway agency, local consultants, the Federal Highway Administration, or industry associations.

1.4.2 Certified Precast Concrete Manufacturers The quality of precast concrete pavement is largely dependent on the quality of the fabricated panels. Precast concrete pavement panels are a specialty item and should only be produced by an established precast plant that has expertise and certification for prestressing and bridge-related production. Temporary prestressing plants are difficult to establish and staff with experienced, qualified personnel and which have mature quality assurance plans in place from start-up. Agencies planning to use PCPS should first consider the precast products that are available regionally. It is recommended that manufacturers of precast, prestressed concrete panels should maintain plant certification by the Precast/Prestressed Concrete Institute.

1.4.3 Agency Materials and Construction Specifications Typical standard specifications for precast, prestressed concrete will not be adequate to address many of the issues necessary for the successful fabrication and installation of PCPS. Supplemental specifications will be needed to address issues that make this product and application unique. Model specifications and special provisions are available for PCPS. They provide guidance for combining an agency’s precast, prestressed concrete and concrete pavement specifications.

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APPLICATIONS FOR PRECAST CONCRETE PAVEMENTS 1.4 Agency Considerations

Some of the more important items that must be addressed when developing specifications for PCPS applications include: 

Concrete mixture design―allow mixture designs to be used that are common to plant-produced precast concrete, so long as they satisfy durability requirements for concrete pavement mixtures



Concrete materials―permit materials such as aggregates, pozzolans (slag and other supplemental cementitious materials), and admixtures to be used that may not normally be required for concrete pavements



Strength Requirements―specify concrete compressive or flexural strength that is appropriate for precast concrete



Surface Finish―allow variance to normal cast-in-place concrete pavement finishing requirements. Some alternative surface textures (e.g., turf drag) are easier to achieve in precast production.



Curing―allow standard precast concrete curing methods to be used, even if they are not common for concrete pavement



Joint Materials―allow expansion joint seals (e.g., neoprene and other preformed materials) to be used even if they are not normally used for concrete pavement



Inspection―provide inspection criteria and inspector training that are appropriate for precast concrete pavement for items such as panel fabrication, base preparation, installation tolerances, post-tensioning, and grouting



Distress and Repair―provide distress identification guidelines and repair procedures that are appropriate for precast concrete pavement



Ride Quality―specify finished pavement ride quality requirements that are appropriate for what can be expected from a precast concrete pavement



Opening to Traffic―specify opening to traffic criteria that are appropriate for precast concrete pavement

1.4.4 Lessons Learned As a result of several PPCP demonstration projects, a number of issues have been identified by the owner agencies. The following is a summary of these important issues including: project type selection and scoping, design, precast production, panel fabrication, and installation. 1.4.4.1 Project Planning and Design  Allow at least 4 to 6 months for design once a project has been identified as a candidate for PCPS. 

Conduct a detailed evaluation of the existing pavement structure (surface, base, subbase, and subgrade layers) to determine the scope of reconstruction. This will provide general guidance for PPCP panel thickness and for determining whether base, subbase, and subgrade reconstruction is necessary.



Obtain an accurate survey of the existing surface (base or existing pavement) prior to project layout and design. For projects with significant geometric variation, more detailed surveys may be required and a digital terrain model developed.



Consider hosting an informational meeting with local and regional fabricators and contractors prior to listing the project. It might be advisable to hold the meeting prior to completing the design in order to gather practical suggestions for details from both groups.



Consider using a product pre-approval process for allowing contractors to submit precast pavement systems that may be unfamiliar (e.g., proprietary systems).

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APPLICATIONS FOR PRECAST CONCRETE PAVEMENTS 1.5 Resources For Additional Information/1.6 Cited References

1.4.4.2 Project Construction  If precast concrete pavement has been selected by the agency as the most appropriate option, do not permit alternative options to be submitted by contractors during bidding or afterward. 

Consider a mandatory pre-bid conference for the project, especially if it is the first project to be constructed in the area.



Consider requiring a trial installation at or near the actual construction site to demonstrate the installation procedures and to identify requirements for equipment.



Ensure that adequate time is available for materials approval tests (e.g., alkali-silica reactivity potential for aggregates used in the concrete mixture) prior to the start date for panel fabrication.



Ensure that adequate time is available in the contract for panel fabrication before installation so that installation does not outpace fabrication.



Diamond grinding the surface of the panels will produce a final product with ride quality comparable to or better than cast-in-place concrete construction.

1.5 RESOURCES FOR ADDITIONAL INFORMATION An online compendium of resources for additional information on precast pavement has been developed by PCI, and is available at the internet address below. This compendium will be continually updated as new information becomes available from current and future projects. www.precastconcretepavement.org

1.6 CITED REFERENCES Buch, N. 2007. Precast Concrete Panel Systems for Full-Depth Pavement Repairs: Field Trials. Report FHWA-HIF-07019, Federal Highway Administration, Washington, D.C. 80 pp. http://www.fhwa.dot.gov/pavement/concrete/pubs/hif07019/07019.pdf Dunn, M. J., M. D. LaViolette, D. K. Merritt, and S. S. Tyson. 2007. Precast Prestressed Concrete Pavement for Rapid Bridge Approach Slab Reconstruction, Proceedings, International Conference on Optimizing Paving Concrete Mixtures and Accelerated Concrete Pavement Construction and Rehabilitation, Atlanta, GA, November 7-9, pp. 347-360. Harrington, D. 2008. Guide to Concrete Overlays―Sustainable Solutions for Resurfacing and Rehabilitating Existing Pavements, Second Edition. National Concrete Pavement Technology Center, Ames, IA. 75 pp. Medina-Chavez, C. I., and M. Won. 2006. Long-Term Performance of Prestressed Concrete Pavement on IH-35 in Texas, In the Proceedings of the International Conference on Long-Life Concrete Pavements, October 25-27, Chicago, IL. Federal Highway Administration, Washington, DC. Merritt, D. K., B. F. McCullough, and N. H. Burns. 2002. Construction and Preliminary Monitoring of the Georgetown, Texas Precast Prestressed Concrete Pavement. Research Report No. 5-1517-01-1. Center for Transportation Research, University of Texas at Austin, Austin, TX. http://www.utexas.edu/research/ctr/pdf_reports/5_1517_1.pdf Merritt, D., S. Tayabji, S. Tyson, and C. Prussack. 2008. Precast Prestressed Concrete Pavement for Heavy-Duty Pavement Applications. Paper presented at the Transportation Systems Workshop, April, Phoenix, AZ. Merritt, D. K., and S. Tyson. 2011. Sustainable Pavements with Precast Prestressed Concrete. In the Proceedings of the Transportation Research Board Annual Meeting, January 23-27, Washington, D.C. Mishra, T., P. French, and Z. Sakkal. 2011. Engineering a Better Road―Use of 2-Way Pretensioned Precast Concrete Pavement for Rapid Rehabilitation. In the Proceedings of the 57th Annual PCI Convention and National Bridge Conference, October 22-26, Salt Lake City, UT. Precast/Prestressed Concrete Institute, Chicago, IL. Nantung, T., J. Firmansjah, E. Suwarto, and H. M. Hidayat. 2010. Design and Construction of Precast Prestressed Concrete Pavement in Indonesia. In the Proceedings of the 3rd International Congress and Exhibition of the fib, May 29-June 2, Washington, D.C. Precast/Prestressed Concrete Institute, Chicago, IL. 1 - 16

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APPLICATIONS FOR PRECAST CONCRETE PAVEMENTS 1.6 Cited References

PCI Committee on Bridges and PCI Bridge Producers Committee. 2011. “State-of-the-Art Report on Full-Depth Precast Concrete Bridge Deck Panels”, First Edition. (SOA-01-1911E). Precast/Prestressed Concrete Institute, Chicago, IL. 141 pp. https://netforum.pci.org/eweb/DynamicPage.aspx?Site=PCI_NF&WebKey=9766331d-1b7d-4c4b-89cbfc801bc30745&ListSearchFor=bridge%20deck%20panels (Fee) Tayabji, S. D., E. J. Barenberg, W. Gramling, and P. Teng. 2001. Prestressed Concrete Pavement Technology Update, In the Proceedings of the 7th International Conference on Concrete Pavements. September 9-13, Orlando, FL. pp. 871-890. http://www.concretepavements.org/ Tayabji, S., D. Ye, and N. Buch. 2011. Modular Pavement Technology. Preliminary Draft Report, Strategic Highway Research Program 2, Transportation Research Board of The National Academies, Washington, D.C. 256 pp.

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DESIGN AND MAINTENANCE OF PRECAST CONCRETE PAVEMENTS 2.0 Introduction/2.1 Features Of PPCP

2.0 INTRODUCTION This second of four documents on the use of precast concrete pavement systems (PCPS), provides guidance for layout, design, and maintenance. Topics included are prestress design (both pretensioning and post-tensioning), joints and load transfer, and numerous other design details. Maintenance considerations are presented. General specifications, drawings of details, and recommendations for maintaining records of performance of the finished pavement are provided. In defining terminology, when PCPS are prestressed, either pretensioned in the fabrication plant, or posttensioned during construction, they are referred to as precast, prestressed concrete pavement or PPCP. Nonprestressed precast concrete panels are called jointed precast pavement systems, or JPPS. Some of the topics in this document on design refer specifically to PPCP, but other subjects can be applied to both systems. Generally, these topics are identified as they are discussed in the text.

2.1 FEATURES OF PPCP Figure 2.1-1 shows a typical panel layout and common features of PPCP which will be discussed further in subsequent sections. While this represents a typical PPCP section, a number of variations have been deployed on projects completed to date. The ability to use full-depth precast concrete panels facilitates rapid construction because the panels serve as the final riding surface of the pavement. Diamond grinding may be required to meet rideability requirements, but an asphalt or concrete overlay is not required. On many projects, a large percentage of “typical panels” are used that greatly simplifies design, manufacturing, and construction. The exception occurs on projects with non-tangent or superelevated sections, or for reconstruction of interior or exterior lanes where the new pavement must match the alignment of the existing longitudinal joints. These panels need to be custom fabricated for a specific location in the project. For projects with complex geometry, it may be necessary to match cast panels. Figure 2.1-1 Identification of Components and features of PPCP Mid-Slab Anchor Panels/Mid-Slab Anchor Sleeves (End Stressing Configuration)

Joint Panel

Central Stressing Panels/P-T Stressing Pockets (Central Stressing Configuration) Base Panels P-T Stressing/Anchor Access Pockets Expansion Joint Prepared Base

Joint Panel

Transverse Pretensioning

Post-Tensioning Bar Tendon (Optional)

Friction-Reducing Membrane Longitudinal Post-Tensioning Strand Tendons

Longitudinal Post-Tensioning Ducts

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Keyway Panel Joints

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2.1.1 Types of PPCP Panels 2.1.1.1 Typical Panels A unique benefit of PPCP for new construction and certain reconstruction projects on tangent sections is that most panels are identical. These “base panels” are not match cast and are generally interchangeable. Base panels make up the majority of a PPCP project and are essentially identical. This results in fewer panel marks (and associated shop drawings), less retooling of the casting form, and allows flexibility in the shipping sequence and installation of the panels. 2.1.1.2 Specialized Panels Specialized panels for most projects are:   

Joint panels that contain expansion joints and post-tensioning hardware Central stressing panels that contain blockouts for stressing post-tensioning tendons Anchor panels with sleeves for anchorage to the underlying base

2.1.2 Cross Section Adaptability Pavement surfaces are constructed with either uniform cross slope or a crown to facilitate drainage. The flexibility of plant precasting process allows virtually any cross section, as shown in Figure 2.1.2-1. The forms determine the thickness of the precast concrete panels. For superelevated or crowned sections, the thickness of the precast concrete panels can be varied asymmetrically to achieve the desired profile. Variable cross sections, however, will require edge forms that are specially made for each shape or forms that are adjustable for a range of profiles. It is desirable to minimize the number of different panel shapes on a project, but equally important that this adaptability is available for those projects with complex geometry. A fundamental difference between conventional cast-in-place concrete construction and precast concrete pavement is the grade of the base versus the profile of the pavement surface. For conventional pavement construction, the base is graded to the proper cross-slope or crown, and a concrete slab of uniform thickness is placed over the base. Precast concrete panels will generally need a true bottom surface, fully supported by the base. A crowned pavement can be achieved by varying the panel thickness and installing the panels on a truegraded base. Alternatively, the base can be graded to the proper crown with separate panels installed on either side of the crown or wherever the cross-slope changes. Figure 2.1.2-1 Pavement Cross Sections that can be Achieved with Precast Concrete Panels X%

X%

a) Uniform Cross-Slope

X%

b) Crowned Cross-Slope―Single Panel

X%

X%

Y%

X%

Z%

c) Asymmetric Cross-Slope―Single Panel

d) Crowned Cross-Slope―Two Panels

An important consideration when using panels with varying thickness is the amount of prestress in the panel. Effective stress in the concrete will vary with thickness and should be taken into account to ensure that thicker sections have adequate prestress and thinner sections are not overstressed. Additionally, the effects of nonconcentric prestressing must be considered for effects on camber.

2.1.3 Prestressing Prestressing creates compressive stress in the pavement slab to reduce or overcome tensile stresses resulting from handling, traffic, and environmental loading. This is intended to reduce or eliminate cracking and greatly enhances the long-term performance of the pavement. Prestressing in both directions is an important benefit of PPCP. Observations of prestressed, cast-in-place concrete pavements by FHWA-sponsored studies in the 1980s 2-2

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(Cable et al.,1985, and Mendoza et al. ,1986) found that transverse prestress is as important as longitudinal prestress. The transverse prestress levels may not need to be as large as the longitudinal prestress. For this reason PPCP features two-way prestressing as described in the following sections. 2.1.3.1 Pretensioning and Post-Tensioning The most common method of prestressing used on the projects to date is a combination of pretensioning in one direction during panel fabrication, and post-tensioning in the other direction after the panels are installed. This is illustrated in Figure 2.1-1. In general, pretensioning is applied in the longest dimension of a precast panel and post-tensioning is applied in the shorter dimension, but through a series of panels. Pretensioning strands and post-tensioning ducts are shown in a panel being set-up for production in Figure 2.1.3.1-1. Typically, panels are post-tensioned together to create a prestressed section, or slab, from 150 to 300 ft in length. Pretensioning provides the long-term prestress service requirements while also counteracting bending stresses in the panel in its longer dimension caused by lifting and handling. In shorter panels (i.e., less than about 12 ft long) or thicker panels (i.e., greater than about 12 in.), pretensioning may not be required to counter lifting and handling stresses, but is desirable for long-term pavement performance. In general, ½-in.-diameter, lowrelaxation, seven-wire strands are used for pretensioning, but ½-in.- or 0.6-in.-diameter strands could be utilized as well. The advantage of smaller diameter strand is a shorter transfer length, effectively prestressing more of the panel. The disadvantage of smaller diameter strands is that more are required to achieve the necessary prestress level. Epoxy-coated strands are also available, but not necessary if sufficient cover of high-performance concrete is provided over the strands. Pretensioning strands are generally located close to mid-depth of the panel, alternating above and below the intersecting post-tensioning ducts. Alternating locations avoids eccentricity of the prestress force. Post-tensioning provides the prestressing in the longitudinal direction of the highway while also serving to connect individual precast panels together to form a continuous prestressed slab. Post-tensioning most often uses single, 0.6-in.-diameter, low-relaxation, seven-wire strands in individual plastic ducts. These strands may be epoxy-coated if the pavement is being constructed in an aggressive environment such as where de-icing salts are used. Smaller strands, multiple-strand tendons, or threaded bar tendons are also options for post-tensioning. Highstrength threaded bar tendons have been successfully used in conjunction with strand tendons on projects completed to date.

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DESIGN AND MAINTENANCE OF PRECAST CONCRETE PAVEMENTS 2.0 Introduction/2.1 Features Of PPCP

Figure 2.1.3.1-1 Formwork and Reinforcement for PPCP Panels. Pretensioning is Longitudinal in the Form (Transverse to Traffic Direction) and Post-tensioning is Across the Form (Longitudinal to Traffic and the Pavement)

2.1.3.2 Two-Way Post-Tensioning An alternative to plant pretensioning is two-way jobsite post-tensioning where post-tensioning ducts are cast into the precast panels in both directions. Post-tensioning may be necessary if local fabricators lack the facilities and expertise for pretensioning. It may also be necessary if short panels need to be connected together across two or more traffic lanes; an example being when two panels form a longitudinal joint at a crowned section, as shown and described in Dunn et al. (2007). Two-way post-tensioning will generally be similar to one-way posttensioning, using single strand tendons. It is not practical to use panels with mating keyways for both transverse and longitudinal joints. Therefore, twoway post-tensioning will generally require an open longitudinal joint between lanes that is grouted prior to posttensioning. Often, a double female keyway configuration is used as shown in. A butt joint between lanes is an option, but may not provide uniform contact between panels across the joint unless it is also filled with grout prior to post-tensioning. If panels are not pretensioned during fabrication, consideration must be given to lifting and handling stresses in the panels. These stresses must be accounted for with nonprestressed reinforcement or by increasing the thickness or decreasing the size of the precast panels. Additionally, two-way post-tensioning will potentially increase the thickness of the panels in order to accommodate ducts in two directions plus any nonprestressed reinforcement. 2.1.3.3 Bonded Post-Tensioning Bonded tendons are defined as those where the ducts in which the tendons are located are completely filled with portland cement grout by injecting the grout through strategically located ports. Bonded post-tensioning tendons provide several benefits. Injecting grout into the ducts ensures structural continuity between the pavement and post-tensioning tendons. It ensures that if any part of the tendon is severed by intentionally or accidentally, prestress will continue to be Document 2 - 4

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transferred to the pavement through bond. Just the local area near the tendon interruption will be affected by the loss of prestress. Grouting provides an additional layer of corrosion protection for the post-tensioning tendons in addition to the protection provided by the concrete cover, tendon duct, and, if it is used, epoxy-coating on the strand. It should be noted that the ducts are not continuous across the panel joints, and therefore this layer of corrosion protection is not present unless a positive duct coupler is used to join ducts between panels. With bonded tendons, portions of the pavement can be removed for utility access or repair, or to replace damage. The prestress beyond the area removed will remain effective. 2.1.3.4 Unbonded Post-Tensioning Unbonded tendons are unique products readily available from manufacturers who coat typical seven-wire strand with special grease and encase it in an extruded plastic sheathing. This protects the strand against corrosion and prevents bond between the strand and the concrete. Most often in construction, these tendons are installed before concrete is placed. However, for PPCP, they would be inserted in the ducts in the precast panels. The grease and sheathing would protect the strand from corrosion and eliminate the need for grouting the duct. Unbonded post-tensioning tendons have not been used for PPCP projects to date. They have been used successfully in cast-in-place, post-tensioned concrete pavements that have been in service for decades, as described by Tayabji et al. (2001). This technology may well have applications in PPCP. An advantage of using unbonded tendons is that it would be possible to detension, remove and replace a tendon should it become necessary. This would permit individual panels or sections of the pavement to be removed and replaced for utility access or if the pavement is damaged. Another advantage of unbonded tendons is the corrosion protection provided by the plastic sheathing where the tendon crosses panel joints. Unbonded tendons would be necessary in order to use PPCP for temporary applications. Precast concrete panels could be removed and relocated by detensioning and removing the unbonded strand, and tensioning it after the pavement was relocated. Note that all tendon anchorages must be encapsulated to ensure that they are adequately protected from corrosion, particularly if they are to be left in place for some time. 2.1.3.5 Temporary Post-Tensioning Temporary post-tensioning is used to clamp the panels together as they are installed. This ensures minimum joint widths between panels and provides a positive force to seat the epoxy joint fill prior to the final post-tensioning. It can also be used to provide temporary post-tensioning when the pavement is opened to traffic prior to completing final post-tensioning. Some level of prestress is desirable when pavement is exposed to traffic when less than all of the panels are in place to make a full post-tensioned slab. Temporary post-tensioning is typically provided by two tendons, either single strands or bars, located at approximately the quarter or third points across the width of the pavement, as shown in Figure 2.1.3.5-1. After every one or two panels are installed, the temporary tendons are tensioned. Threaded bar tendons can be spliced onto the previous bars as each panel is installed. They may be left in place, used as final post-tensioning tendons. Strand tendons usually need to be replaced with new strand for the final tendons because multiple “bite” indentations are left in the surface of the temporary strand by the chuck jaws as each panel is installed and the strand tensioned.

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Figure 2.1.3.5-1 Temporary Post-tensioning used to Clamp Panels Together During Installation

a) Tensioning Strand Tendons

b) Tensioning Threaded Bar Tendons

2.1.4 Keyed Joints Keyways along mating edges of the precast concrete panels ensure vertical alignment between panels during installation. They also provide some degree of load transfer between panels before and after applying the longitudinal post-tensioning. Keyways may also be required for a longitudinal joint between panels, as described in Section 2.1.4.1. 2.1.4.1 Transverse Joints Transverse keyways are typically tongue and groove in shape and serve primarily to align the panels vertically during installation. This ensures there is not a lip or “fault” at the top of the joint between panels. Ideally, a keyway should extend across the full width of the joint, including shoulders that may be part of the panel. In some cases, however, it is necessary to terminate the keyway if the thickness of the panel is reduced and the keyway cannot be accommodated in the panel thickness. The keyway should extend at least across traffic lanes, even if it is not present in the shoulder section of the panel. Transverse tongue and groove keyways are typically not match cast. This facilitates much faster production by allowing panels to be cast on long-line beds. Because the keyways are not match cast, some tolerance is required to permit minor variations of the shape. For projects completed to date, the keyway dimensions have been defined so the vertical faces above and below the keyway will be in contact a minimum of 2 in. when the panels are assembled, as shown in Figure 2.1.4.1-1. As discussed earlier, on projects that require maintenance of precise geometry, it may be necessary to match cast the panels, in which case it would not be necessary to consider joint tolerances. An alternative to tongue and groove keyways is an open keyway that is filled with grout after the panels are in place and prior to post-tensioning (Figure 7). Open keyways will not provide the benefit of ensuring vertical alignment between panels, but do provide more flexibility in compensating for slight misalignment of panels. It is important that non-shrink grout is used that is properly bonded to both faces of the keyway. This may require that the surfaces of the panels be cleaned of any oils, grease, or curing compound prior to installing the panels. If the grout is not properly bonded and becomes loose in the keyway, it will likely spall out and possibly damage the top edges of the panels on either side.

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Figure 2.1.4.1-1 Tongue and Groove Panel Keyway

2” Min.

H+1/8”

D-1/8”

H

2” Min.

H+1/8”

2” Min.

H

D

a) Typical Keyway Dimensions

b) Keyway Joint Shown in Installed Panels

2.1.4.2 Longitudinal Joints If more than one precast panel is used to form the width of a pavement section, there will be longitudinal joints between panels. While butt joints have been used successfully on post-tensioned projects to date, keyed longitudinal joints have also been used. Keyed longitudinal joints are commonly an open keyway that is filled with grout or a pea gravel concrete mixture, as shown in Figure 2.1.4.2-1 in panels used in Iowa for bridge approaches. The open joint provides more tolerance for misalignment of panels, and is favored over trying to match keyways both longitudinally and transversely. Ideally, longitudinal joints between precast panels should be post-tensioned to maintain the integrity of the joint, particularly for joints that are filled with grout or concrete, which are susceptible to shrinkage during curing. Figure 2.1.4.2-1 Longitudinal Panel Joint

a) Facing Female Keyways in a Longitudinal Joint

b) Joint Filled with Grout and Finished

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DESIGN AND MAINTENANCE OF PRECAST CONCRETE PAVEMENTS 2.2 Design

2.2 DESIGN 2.2.1 Geometric Considerations One of the first considerations for design of a PCPS is the roadway geometry. New pavement not abutting existing adjacent pavement may be designed by specifying horizontal and vertical curvature and associated superelevation transitions. New precast pavement installed next to existing pavement will require a detailed survey of the existing pavement in order to fabricate new precast panels to match. Careful surveying is sufficient for most situations although match casting may be required in very unique cases. For tangent sections, even those with some degree of vertical curvature, standard panels with tongue and groove joints may be used. However, a survey should still be conducted, even though less detailed, to identify potential changes in alignment that might appear to be perfectly tangent. When PCPS are constructed on a tangent section adjacent to existing pavement, the edge of the existing pavement must be surveyed to document deviations in alignment. If deviations from a tangent line are found, the new panels must be fabricated accordingly. Alternatively, the existing pavement may be cut to a true tangent line that is slightly offset from the non-tangent existing edge and the new panels fabricated to that line. When PCPS are constructed on a new alignment, a reference line should be surveyed and marked on the surface of the base, and the PCPS panels aligned to that mark. Alignment of every panel is very important so overall alignment is maintained. If the first panel is not set exactly perpendicular to the longitudinal reference line, the alignment will quickly wander from the centerline.

2.2.2 Panel Layout Panel layout is highly dependent on project site constraints. PCPS can be used for single or multiple lane construction, but this will be dictated by the available work area (e.g., the number of lanes that can be closed at one time) and equipment requirements. PPCP panels are commonly laid out with the long axis perpendicular to the flow of traffic or direction of the roadway. This permits a single precast panel to span multiple lanes and shoulders as required. The panels are then post-tensioned together in the longitudinal, traffic direction across the short dimension of the panels. If construction is limited to a single lane, the panel dimensions need to be equal to the width of a single lane (plus perhaps one shoulder). Alternatively, it may be desirable to orient the precast panels with the long dimension of the panel in the direction of traffic. Ideally, whatever panel layout is selected, the longitudinal joint between panels or between a panel and existing pavement should not coincide with a wheel path. Projects with complex geometry (horizontal curves, superelevated sections, intersections, etc.) will require a very precise precast panel layout. A detailed survey will be necessary in order to establish the dimensions and plan location of each panel to be fabricated. For these applications, the agency should obtain grade and cross-slope information before beginning design, and should also provide this information to the contractors prior to bidding.

2.2.3 Panel Thickness Panel thickness must be selected to meet all geometric constraints specific to each project. Thickness should also be optimized for material savings and to reduce the weight of the panels. If it is necessary to match the thickness of an existing pavement that will remain in place, either at ends or alongside the PPCP section, the panel thickness may be dictated by those existing conditions. In some locations, the thickness may be restricted, for example, at bridge underpasses. As discussed in Section 2.1.2, panel thickness may also be varied to match the desired pavement cross section, such as a crowned section. If there are no specific geometric constraints, the thickness of the precast panel should be selected to optimize material usage, by making the panels as thin as possible without compromising long-term performance and the stability necessary to safely lift and handle them. The panels should not be so thin that they deflect significantly when lifted, as this will affect fit-up of the keyways during installation unless more than a four-point lifting configuration is used. The panels must be thick enough that the keyways can function effectively in the edges of the panels. It should also be noted that thinner panels may result in higher deflections and deflection-related stresses at the expansion joints. Use of thinner panels may require special attention to providing better base support beneath the expansion joints. 2-8

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When selecting the thickness, consider the reinforcement, pretensioning, and post-tensioning hardware that will be cast into the panel, as depicted in Figure 2.2.3-1. Thickness should be adequate to provide necessary concrete cover for reinforcement, pretensioning, and post-tensioning tendons and other hardware, given the environment where the pavement will be constructed. A practical minimum panel thickness will generally be 8 in. Thinner panels may be too flexible during handling, and may not provide adequate space for all of the embedments plus required concrete cover, particularly if the top surface will be diamond ground after installation. For projects completed to date, panels of uniform thickness have been at least 8-in. thick. For panels with variable cross-sections, thickness has been as much as 13 in. at the pavement crown, and tapered to as little as 5¾ in. at the edges of pavement shoulders. No post-tensioning ducts are present in these thin sections. Figure 2.2.3-1 Multiple "Levels" of Reinforcement to Consider when Determining Thickness of Panels. Pretensioning Concrete Strand Cover

Post-Tensioning Ducts

Nonprestressed Reinforcement

2.2.4 Panel Plan Dimensions Panel dimensions will be dictated by the project requirements and constraints. These include the maximum width that can be paved with a single precast panel based on lane closure restrictions and shipping constraints, such as the maximum width and weight that can be shipped by truck and handled in the field. In general, the largest practical panel size should be specified in order to maximize production rates for both fabrication and installation. However, safe handling of the panels both in the plant and on site should be carefully considered when selecting the size. Consideration should be given to the size and type of crane that will be required on the site, and the available clear space around the installation, particularly if the panels are being installed next to live traffic or near overhead restraints. Consideration should also be given to the size of the casting bed required. A common width for panels cast on a long-line bed is 8 to 12 ft for most precast plants. If panels are individually cast or match cast, wider panel widths may be possible, keeping delivery constraints in mind. Before selecting the final panel dimensions, check with local precast producers to ensure the dimensions are practical. Shipping costs may affect panel dimensions, particularly if the panels are to be shipped long distances. Large and heavy panels may require oversize load permits, but the increase in production efficiency with larger panels may offset the hauling permit cost. On the other hand, more than one smaller panel may be shipped on each truck, but the decrease of production rate may offset the savings of fewer trucks. Similar to how the thickness of panels is varied to meet project requirements, panel dimensions can be varied as well. Custom panel dimensions can be specified for projects with complex geometry. It should be noted, however, that increasing the length or width of the panels may also increase the required prestress and thickness to control excessive stresses during handling. For projects constructed to date, a panel size of 12 by 36 ft has been used with success, but required a larger crane for handling.

2.2.5 Connecting to Existing Structure Tying PPCP sections into existing pavement, shoulders, or barriers should be evaluated carefully during design. In general, only the mid-length portion of a section of PPCP will be anchored to the underlying base and therefore remain stationary. The ends of the section, near the expansion joints, will move from elastic shortening during 2-9

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post-tensioning and due to expansion and contraction from daily and seasonal temperature variations. Therefore, it is recommended that only the mid-section of the PPCP slab (e.g., within 10 ft of mid-slab anchors) be tied to existing pavement or shoulders. For barriers, it is recommended that isolation joints be provided between PPCP and the barrier. The terminal ends of a PPCP section may be connected to existing pavement to provide load transfer. This is done through the half of the joint panel that abuts the existing concrete pavement but is isolated from the posttensioned section by the expansion joint. This half of the joint panel can safely be tied to the existing pavement using dowel bars (if joint movement must be accommodated) or tie-bars (if joint movement does not need to be accommodated) through either closure pours or slots cut into the existing pavement, as shown in Figure 2.2.5-1. Figure 2.2.5-1 Options for Connecting Precast Pavement to Existing Pavement at Terminal Ends using a Closure Placement (Left) or Dowel/Tie-Bar Slots (Right). Closure Pour

Existing Pavement

Dowel Bars or Tie-Bars (drilled and epoxied into existing pavement)

Dowel Bar/Tie-Bar Slots (sawcut into existing pavement)

Precast Pavement Panel

Dowel Bars or Tie-Bars (cast into precast panel)

Existing Pavement

Dowel Bars or Tie-Bars (cast into precast panel)

2.2.6 Base Support 2.2.6.1 Level of Support PCPS construction must accommodate a wide range of subgrade and base conditions, but it is essential that adequate support be provided. For new construction, the underlying base and subgrade layers can be properly engineered and constructed to provide optimal support. For reconstruction and overlays, however, subgrades, bases, and existing pavement may simply be in such poor condition that they will need to be replaced. Deflection testing of an existing pavement structure where the PCPS will be constructed will help determine the level of support available, which can then be used to design the PCPS section or indicate that the base and subgrade need to be reconstructed with the pavement. The degree of support actually provided must be estimated. While cast-in-place concrete pavement uniformly conforms to the underlying base surface, PCPS panels rest on top of the high points of the base. Nearly full contact with the base must be provided. Grouting beneath the precast panels will help to provide full support. If large voids are anticipated, grouting under the panel must be required, or the base re-graded to provide fuller support. 2.2.6.2 Base and Subgrade Preparation There are no specific requirements for the type of base or subgrade materials used beneath PCPS. On projects completed to date, a variety of materials have been used, and selection is based on common practice in the location where the project was constructed. Methods and materials used successfully include dense graded hotmix asphalt, permeable asphalt treated base, lean concrete base, pervious concrete, crushed stone aggregate, and granular materials. Base materials used in previous projects are shown in Figure 2.2.6.2-1. It has been observed that the panels tend to settle into flexible materials such as the asphalt bases and fresh pervious concrete, while they tend to rest on top of the harder bases such as lean concrete and the aggregate materials. A tolerance for the base surface of ±⅛ in. in 10 ft, as measured under a 10-ft-long straightedge, is typically specified, and has been achieved by contractors. For the more rigid bases, such as lean concrete, where it is 2 - 10

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difficult to construct the base to such small tolerance, the tolerance can be increased to ±¼ in. in 10 ft. However, relaxing the tolerance will likely result in more voids beneath the panels, and under-slab grouting will be required to fill those voids, possibly even before the pavement is opened to traffic. 2.2.6.3 Friction-Reducing Layer One of the necessary components of PPCP is a friction-reducing layer or membrane between the PPCP and underlying base. Because PPCP consists of long (150 ft or longer) post-tensioned slabs, significant movement of these slabs is anticipated during daily and seasonal temperature variations and during initial post-tensioning. The friction-reducing layer helps decrease frictional restraint stresses induced in the pavement slab during expansion and contraction, ensuring a greater effective prestressing force in the slab. A single layer of 6 mil minimum thickness polyethylene sheeting has been found to be an economical and constructible material for this layer. If drainage is a concern, permeable geotextile fabric has also been used successfully as a friction-reducing layer. Both materials are shown in Figure 2.2.6.3-1. Figure 2.2.6.2-1 Base materials used for PPCP

a) Dense-Graded Asphalt Concrete (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Permeable Asphalt Treated Base

c) Lean Concrete

d) Crushed Stone

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f) Granular Base

e) Pervious Concrete Figure 2.2.6.3-1 Friction-Reducing Membranes

a) 6-Mil Polyethylene Sheeting

b) Geotextile Fabric

2.2.7 Nonprestressed Reinforcement The amount of nonprestressed reinforcement in PPCP panels is typically minimal. In general, if the panel is pretensioned, the American Association of State Highway and Transportation Officials (AASHTO) LRFD Specifications requires a minimum area of temperature reinforcement only in the nonpretensioned direction, if the spacing of the pretensioning strands meets the requirements of LRFD Article 5.10.3.4. The amount is a ratio of 0.0018 times the gross section area (a simplification of LRFD Eq. 5.10.8-1, see LRFD Art. 5.10.8). For nonpretensioned panels, but those that will receive two-way post-tensioning on site, this minimum reinforcement area should be provided in both directions since the panels will be subjected to temperature variations prior to application of the post-tensioning.. Depending on the size of the panels, however, lifting and handling stresses should be calculated and additional reinforcement provided if required. Additional nonprestressed reinforcement will be required in the post-tensioning anchorage regions as bursting reinforcement and around blockouts to arrest cracks that may form from the corners of the blockouts.

2.2.8 Prestressing Requirements Prestressing requirements are generally determined by an analysis of stresses anticipated in the finished pavement over time, as well as stresses due to lifting and handling of the precast concrete panels. When determining prestress levels, prestress losses must be accounted for. These losses include: elastic shortening, creep, shrinkage, and tendon relaxation. 2 - 12

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2.2.8.1 Pretensioning Pretensioning of the panels provides the beneficial precompression for long-term pavement performance, while countering stresses from lifting and handling. Lifting and handling stresses can be calculated using methods shown in the PCI Design Handbook (2010), using lifting configurations and panel dimensions anticipated for the project. In general, pretensioning requirements for lifting and handling are determined so that the panel remains in compression during handling, taking into account its lower concrete strength and the “suction” force during removal from the form. Long-term prestress requirements from pretensioning are determined in the same manner as long-term prestress requirements from post-tensioning (see the following section), taking into account prestress losses over time, curling stresses, and traffic loading on the pavement. Frictional restraint stresses due to slab-base interaction are not as critical for pretensioning due to the relatively short length of the slab in the transverse direction. As a general guideline, 200 psi compressive stress in the panels after transfer of force at the fabrication plant should provide adequate long-term prestress from pretensioning. 2.2.8.2 Post-Tensioning Long-term stresses in the pavement slab necessary to determine the level of longitudinal post-tensioning include those from wheel loads and those caused by environmental stresses, such as expansion, contraction, and curling. In determining effective prestress levels from post-tensioning, prestress losses from slab-base frictional restraint, elastic shortening, creep, and shrinkage must also be taken into account. It should be noted that because the panels have been precast, much of the concrete shrinkage will have occurred prior to post-tensioning, resulting in less prestress loss due to shrinkage than is typical in pretensioned concrete or seen from cast-in-place concrete. Additionally, losses during tensioning due to strand-duct friction and wobble (alignment deviations along the duct) must also be accounted for. Stresses from wheel loads can be determined through layered elastic analysis using the properties (thickness and modulus) of the underlying pavement layers. If not explicitly determined by the layered elastic analysis, these stresses should be increased to account for edge loading on the pavement slab if wheel loads are anticipated on the edge of the slab. Stresses from environmental effects, including frictional restraint stresses due to slab expansion and contraction, and stresses due to slab curling can be calculated by finite element modeling of the pavement slab (Mendoza et al., 1986). Prestress losses can be estimated using methods presented in the PCI Bridge Design Manual (2011), and the PTI Post-Tensioning Manual (2006). The general guideline for post-tensioning prestress levels is a minimum of 200 psi compressive stress in the PPCP at completion of construction (after all construction-related losses) at all points along the pavement. However, whenever possible, an analysis of stresses in the pavement slab should be used to establish prestress requirements.

2.2.9 Post-Tensioning Issues Other considerations for post-tensioning include layout of the post-tensioning tendons, stressing locations, treatment around post-tensioning ducts in joints between panels, and transverse post-tensioning. There is no single solution for every project to address these issues, but there are a number of successful best practices that have been utilized in previous projects. 2.2.9.1 Tendon Layout and Stressing Locations Post-tensioning tendon layout and stressing locations are generally governed by project constraints and the layout of the precast panels. Ideally, post-tensioning tendons should be stressed at the ends or side faces of the precast pavement slab, similar to conventional slab-on-ground construction. However, if access to the ends and sides of a precast pavement slab is blocked by adjacent existing pavement, shoulders, or a previously installed adjacent precast concrete pavement slab, stressing can be accomplished in blockouts or stressing pockets cast into the panels. This allows the post-tensioning anchors to be accessed from the top surface of the pavement. Longitudinal post-tensioning tendons are usually single strands with single-strand anchors (preferably encapsulated for corrosion protection) at both ends of the tendon. Tendons are usually straight, which minimizes losses due to tendon curvature. However, looped post-tensioning tendons have been used successfully in the past in cast-in-place post-tensioned concrete pavement (Mendoza et al., 1986). The tendons are typically centered at 2 - 13

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mid-depth of the panels. However, shifting the tendons slightly below mid-depth (e.g., ½ in.) will provide an eccentric moment at the ends of the slab to help counteract any upward curling of the slab and associated loss of support at the expansion joints. Two methods have been used to post-tension slabs longitudinally: end stressing and central stressing, as illustrated previously in Figure 2.1-1, and shown below in Figure 2.2.9-1. In the end stressing method, pockets are cast into the special joint panels at the ends of each post-tensioned section or slab (varies in length from 150 to 300 ft). Post-tensioning tendons are then fed into the ducts from the stressing pockets at one end, through all the panels, to the pockets at the other end of the post-tensioned section. In the central stressing method, pockets to access the post-tensioning ducts are cast into either one or two panels at the center of the post-tensioned section and in the end joint panels. The strands are fed into the ducts from the center stressing pockets in opposite directions to the pockets in the joint panels where strand anchors are attached. In the central stressing pockets, the two strands lapping from opposite directions are spliced together using a special “ring” anchor or “dog bone” anchor that allows both strands to be tensioned simultaneously by pulling on one while reacting against the other. Figure 2.2.9.1-1 Stressing Techniques used for PPCP

a) Central Stressing (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) End Stressing Document 2 - 14

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The advantage of central stressing is that the tendon length is effectively half of the slab length, reducing losses in the tendon during stressing. The anchors at both ends of the slab are fixed-end anchors (also referred to as deadend anchors). The advantage of end stressing is that it eliminates the need for one or more unique center stressing panels, reducing the number of different types of panels, and reducing the number of blockouts that need to be filled after stressing. All stressing pockets should be large enough to accommodate the stressing ram that will be used to tension the tendons. In general, when taking into account elongation of the strands during stressing, monostrand stressing rams will be too long for a typical stressing pocket, and the addition of a “curved nose” ram stressing extension will be necessary. 2.2.9.2 Transverse Post-Tensioning When two or more sections of PPCP are installed next to each other creating a longitudinal joint (e.g., for multiple lane projects), transverse post-tensioning may be necessary for connecting these sections together across the longitudinal joint. If the panels are pretensioned in the transverse direction, transverse post-tensioning needs to be only enough to keep the panels tight to the joint and not to provide the total transverse prestressing force. It has been found that one or two ½-in.- or 0.6-in.-diameter post-tensioning strands per panel should be adequate for connecting adjacent sections together across the joint and holding it tightly closed.

2.2.10 Corrosion Protection Strategy All projects should be designed with a clearly defined corrosion protection strategy, particularly those constructed in aggressive environments where the pavement will be exposed to chlorides from groundwater, salt spray, or deicing chemicals. The corrosion protection strategy should encompass concrete mix design and supplemental corrosion protection features for the various steel components embedded in the panels, including reinforcement, prestressing tendons, and hardware. 2.2.10.1 Concrete Mix Design The concrete is the first level of protection against corrosion for embedded steel. Concrete mixtures should result in low permeability and good freeze-thaw resistance. This requires the right combination of cement, supplementary cementitious materials, and admixtures to reduce permeability while providing adequate air entrainment. Aggregates used in the concrete should meet the requirements for abrasion resistance and polish resistance typically required for concrete pavements by the owner agency. Aggregates should also not be susceptible to alkali-silica reactivity (ASR) and should preferably be selected from an agency pre-approved source. In addition to a low-permeability, freeze-thaw-resistant concrete mixture, providing adequate concrete cover is essential. In general, a minimum of 2 in. of concrete clear cover should be provided between any reinforcement or prestressing strands, and exposed surfaces of the pavement. However, less-aggressive environments may permit concrete clear cover of 1.5 in. Specification of concrete cover with respect to the top surface of the panels should take into account diamond grinding of the top surface after installation. Grinding requires a minimum of ½ in. of additional concrete cover. 2.2.10.2 Corrosion Protection In addition to the concrete, more “layers” of corrosion protection are available for embedded steel items. For reinforcement, epoxy-coated steel adds corrosion protection. For lifting anchors, epoxy-coated, galvanized, and stainless steel anchors are available. For post-tensioning tendons, the duct and grout (for bonded tendons) provide additional layers of protection. However, for locations where the duct is not normally continuous, such as across joints between panels, positive connection couplers should be provided to ensure continuous protection of the tendon. Plastic duct (polyethylene or polypropylene) provides an impervious, corrosion-proof layer of protection. For post-tensioning anchors, fully encapsulated anchors are available, and are generally supplied as a system together with plastic ducts. For the grout, low permeability, prepackaged grout manufactured specifically for post-tensioning tendons should be 2 - 15

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specified for bonded post-tensioning tendons. Finally, epoxy-coated strands and bars are available for the tendons.

2.2.11 Expansion Joints The expansion joints cast into the joint panels located at the ends of a slab or section are designed to accommodate or “absorb” the daily and seasonal expansion and contraction movements and post-tensioning shortening of the pavement slab. Expansion joints should be selected to accommodate the anticipated slab movement, while also providing load transfer across the joint for the types of traffic that are expected to use the pavement. 2.2.11.1 Expansion Joint Requirements The width of the opening in the expansion joint varies over the life of the pavement. It is governed primarily by the slab length, pavement thickness, prestress level, slab-base friction characteristics, and seasonal temperature variations at the project location. Expansion joint width is also affected to a lesser extent by the concrete materials used for the precast panels, including the coefficient of thermal expansion, and creep and shrinkage properties. It is important to note that the total expansion joint movement will change over the life of the pavement from creep due to the prestress force, and relaxation of the post-tensioning tendons, among other factors. Providing adequate load transfer across PPCP expansion joints is critical as the joints are wider than conventional jointed concrete pavement and there is no contribution from aggregate interlock. Expansion joints without positive load transfer will fault under heavy wheel loads and eventually fail. Steel dowel bars have proven to be an effective load transfer device for PPCP joint panels, and should be included in these joints, regardless of the type used. 2.2.11.2 Type of Joints and Materials Three types of expansion joints have been used successfully on PPCP projects. These are shown in Figure 2.2.11.2-1. Armored expansion joints, which are similar to those used for concrete bridge decks, have a steel structure on both sides of the joint that gives the joint additional toughness under heavy dynamic wheel loading. This joint detail was used successfully for a PPCP demonstration project in Texas (Merritt et al., 2002), as well as for a castin-place, post-tensioned concrete pavement, also constructed in Texas, and has performed very well for over 25 years (Medina-Chavez and Won, 2006). Armored joints should be used when the expected expansion joint movement is from 2 to 4 in. In this joint, it is critical that the steel armor is anchored to the precast panel using bars welded to the steel seal receivers. An advantage of the joint detail is that the post-tensioning anchors can be bolted to the steel joint, ensuring the post-tensioning force is transferred directly to the expansion joint. A disadvantage of the joint is that if the concrete is finished flush with the steel, the joint cannot be diamond ground when the pavement is surfaced for smoothness. However, recessing the steel seal receivers approximately ½ in. below the top surface of the concrete, allows space for grinding. For the joint seal, armored joints typically use a preformed neoprene seal that is held in place by the steel seal receivers. Ordinary dowelled joints are a second option to accommodate expansion. These joints are formed by casting each half of the joint panels separately, creating a butt joint between the halves, with dowel bars connecting the two halves. These joints are typically sealed with multi-cell preformed elastomeric joint seals that are bonded to the faces of the expansion joint. Plain dowelled joints will not have the toughness of the armored joint or header joint, so they should be used only when minimal movement of less than 1 in. is expected. Plain dowelled joints have been used on several PPCP projects to date, exhibiting good performance. A third option for expansion joints is a header joint. These joints are commonly used for bridge decks that have hot mix asphalt surfacing. Header joints are formed by casting a shallow, 1- to 2-in.-deep recess 3 to 4 in. wide on both sides of the expansion joint. This recess is filled with proprietary header material that is slightly more flexible than concrete, giving the joint additional toughness at the top surface where wheel loads impact the joint. The additional toughness permits use for wider expansion joints, similar to armored joints. These joints are usually sealed with silicone sealant poured in the recess against a backer rod that can accommodate the anticipated movement. The extension and compression capacity of the silicone material will dictate the maximum and minimum widths for this joint. They are assumed to be able to accommodate joint movement of 1 to 2 in. One 2 - 16

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of the advantages of a header joint is that the header material can be diamond ground with the surrounding pavement surface, minimizing local roughness at the expansion joint after grinding. It is also not susceptible to corrosion in aggressive environments. The header material and silicone seal, however, will have a limited lifespan and require periodic replacement throughout the life of the pavement. While there is no perfect solution for expansion joints, several options have proven successful for PPCP. Durability and maintenance considerations should be weighed when selecting the expansion joint detail, particularly considering the traffic demands. Figure 2.2.11.2-1 Types of PPCP Expansion Joints

a) Armored Joint Before Placement in Form (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Armored Joint in Service

c) Plain Dowelled Joint with Elastomeric Seal

d) Header-Type Joint with Silicone Seal

2.2.11.3 Joint Width There are two consideration of joint width for expansion joints: the maximum expected width and initial joint width. Maximum joint width is the anticipated maximum opening of the expansion joint over the life of the pavement. The maximum width is used to select the type of expansion joint and joint seal expansion properties. The maximum anticipated joint width can be varied by adjusting the post-tensioned slab length and prestress levels. The frictional restraint and slab temperatures are assumed fixed for a project. Initial joint width is the width of the expansion joint after installation on site. The initial joint width is critical for ensuring that the joint will never fully close, which could cause a pavement blowup. The initial width will also 2 - 17

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affect the maximum joint width. The initial width can be set to a specified dimension at the fabrication plant, or it can be set on site by forcing the two halves of the joint panel apart. Initial joint width must be determined through prediction of joint movement over the life of the pavement.

2.2.12 Typical Panel Joints Careful consideration must be given to the treatment of the joints between panels, particularly where the posttensioning tendons cross the joints. If the ducts are not properly sealed at the joints, grout will leak from these joints when the ducts are pressure grouted. These locations can provide a location for water and deicing salts to come in contact with the post-tensioning tendon. An epoxy material suitable for bonding hardened concrete to hardened concrete, applied liberally to the mating faces, has been found to be an effective joint seal. The epoxy not only helps to seal the joint, but also acts as a lubricant in the keyways when the panels are assembled. Care must be taken to prevent the epoxy from entering and blocking the duct. A compressible neoprene or foam rubber gasket placed around the end of each duct will help to prevent epoxy from entering the ducts during assembly, and prevent grout from leaking from the ducts during tendon grouting. For the best possible seal, a positive coupler that provides a watertight seal between duct segments should be used in combination with the epoxy. For all projects, but particularly for projects constructed in aggressive environments where there is a higher potential for tendon corrosion, this combination of epoxy plus duct couplers is recommended.

2.2.13 Functional Considerations Functional considerations for precast pavement are common to all pavements. These include safety, such as skid resistance and splash and spray, as well as user-driven considerations, such as ride quality and tire-pavement noise. 2.2.13.1 Skid Resistance The skid resistance of a pavement surface is primarily controlled by the type of texturing applied to the surface and the type of aggregates used in the pavement. Texturing practices for precast pavement should not deviate significantly from common practice for concrete pavement. However, a uniform tined surface will be more difficult to achieve since it is applied to each precast panel individually, rather than to the continuous finished pavement in place. Diamond grinding, which is commonly required for achieving ride quality standards, will provide adequate texture, depending on the agency’s requirements. If diamond grinding is required, a broom or carpet turf drag texture applied during panel fabrication will generally provide adequate texture prior to diamond grinding. The durability of surface textures over time is significantly affected by the aggregates used in the concrete mixture. Durable, abrasion- and polish-resistant aggregates should be specified to help ensure long-term durability of the surface texture. Requirements for these aggregates should not deviate significantly from typical requirements for concrete pavement aggregates. 2.2.13.2 Ride Quality Ride quality requirements have progressively become more stringent, particularly for interstate and other primary highways. In general, the ride quality of PPCP as constructed will be satisfactory for lower-speed facilities (local roads, ramps, intersections, frontage roads, etc.), and will generally be acceptable for “temporary” opening of the pavement to traffic (i.e., during construction) even on interstate and primary highway facilities. However, for higher-speed facilities, diamond grinding may be required to bring the PPCP surface into compliance with ride quality standards. Diamond grinding is commonly used for cast-in-place concrete and asphalt pavements, and is a cost-effective method to achieve ride quality. 2.2.13.3 Tire-Pavement Noise Tire-pavement noise is influenced by the surface texture applied to the pavement surface. Certain textures, such as longitudinal tining and diamond grinding have been found to result in less objectionable tire-pavement noise than other common textures such as transverse tining. Some of the quietest surface textures are exposed aggregate and porous surfaces. These surface textures can be readily achieved in a plant-produced pavement panel, but diamond grinding of these surfaces to correct ride quality in-situ would remove the exposed aggregate surface. If a tire-pavement noise requirement is included in a project, careful consideration should be given to the type of texturing specified or allowed. 2 - 18

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2.2.13.4 Splash and Spray Surfaces that tend to exhibit the least splash and spray are porous surfaces. These surfaces are not common for concrete pavement, but have been used in Europe and in experimental projects in the United States. While this type of surface is conceivably much more achievable with plant-produced pavement panels, the cost will likely be significantly higher than conventional pavement textures, and consideration should be given to the effects that diamond grinding (for ride quality) would have on the surface.

2.3 PPCP MANAGEMENT CONSIDERATIONS 2.3.1 Performance Monitoring PCPS are intended to be low-maintenance, long-life solutions. Performance of PCPS sections constructed to date indicates that very little maintenance is required (Tayabji and Ye, 2010). As with all pavements, the performance of PCPS should be monitored routinely to identify maintenance issues that could arise and if repairs are needed. 2.3.1.1 Pavement Performance Concrete pavement is evaluated for functional and structural performance. Traditionally, functional performance only encompasses smoothness or ride quality, but may also consider skid resistance and tire-pavement noise. Structural performance encompasses pavement distresses, joint load transfer, and to some extent, base and subgrade performance. Initial smoothness and ride quality should conform to the state agency’s standard requirements for concrete pavement. Diamond grinding can be used to bring the finished pavement to within these requirements. The initial smoothness and ride quality should be used as the baseline, and future smoothness and ride quality measurements should be compared with this baseline to evaluate functional performance over time. If desired, skid resistance and tire-pavement noise can be monitored in the same fashion. Structural performance evaluation should identify distress that appears in the pavement. A project-level condition survey of the entire pavement should be conducted following construction to identify distress for comparison with future condition surveys. Typical distress that may be observed in PPCP is described in the paragraphs that follow. Structural performance evaluation may also include an assessment of deflections and load transfer across joints. Deflections are generally measured using the falling weight deflectometer (FWD), which is a stationary test device that will require lane closures during testing. Deflection testing should be conducted at selected joints between panels, at all expansion joints, and at selected locations in the middle of individual precast panels. Load transfer at joints between panels should be near 100%, as these joints are locked together with keyways, epoxy, and post-tensioning. Load transfer at expansion joints will normally perform at 70 to 100%. Although load transfer less than 80% may be cause for concern for conventional concrete pavements, lower load transfer efficiency can be expected for PPCP expansion joints since the joints are much wider, there is no contribution from aggregate interlock, and there may be voids beneath the precast panels. Deflection testing at locations in the middle of precast panels can provide an indication of the level of support beneath the pavement and whether or not voids are present. Testing at several locations should provide a baseline for deflections. If deflections at certain locations are significantly higher than this baseline, voids may be present. Under-slab grouting can be used to fill voids if there is concern that the voids will affect long-term performance. 2.3.1.2 Instrumentation Instrumentation of PPCP can provide useful information for validating design assumptions and identifying potential causes of performance issues. Temperature sensors, strain gauges, and displacement transducers are the most commonly used instruments. Temperature sensors are used to monitor mid-depth slab temperatures, as well as top-to-bottom slab temperature gradients. Thermocouples or self-powered internally logging temperature sensors can be used to monitor temperature. At a minimum, temperature sensors should be embedded at 1 in. from top and bottom surfaces and at mid-depth of the precast concrete panels in at least one or more locations along the slab. Sensors should be kept a minimum of 2 ft from slab edges or expansion joints. 2 - 19

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DESIGN AND MAINTENANCE OF PRECAST CONCRETE PAVEMENTS 2.3 PPCP Management Considerations

Strain gauges are used to monitor strains in the concrete and prestressing tendons. These strains can then be converted to stresses given the modulus of elasticity of the concrete and prestressing steel. Measuring concrete and prestressing steel strains (and stresses) can help validate original design assumptions. Vibrating wire strain gauges are the most common devices used for concrete, but conventional strain gages mounted to pieces of reinforcing steel embedded in the concrete can also be used. Strain gages for prestressing steel are normally mounted to the post-tensioning strands prior to stressing and measure the strains during post-tensioning. New strain gauge technology, such as inductive loop strain gauges are also available as a less-intrusive solution. Monitoring post-tensioning tendon strain gauges over time will help validate design assumptions for posttensioning tendon stresses initially and over time. Displacement transducers are used primarily to monitor horizontal and vertical slab movement. These transducers are typically mounted at the corners of the expansion joints to monitor expansion joint movement and vertical slab movement due to slab curling. For measuring expansion joint movement, the width of the expansion joint as well as the relative movement of one or both slabs on either side of the expansion joint should be monitored. For measuring slab curling (vertical movement), the gauges must be mounted to a fixed reference separate from the slab (typically a concrete lug in the ground next to the slab), and the movement of the corners of each slab monitored. Total station surveying equipment has been used previously for this purpose, but does not provide adequate resolution for the small deflections typical of slab curling (Luckenbill, 2009). Several PPCP projects constructed to date have included instrumentation embedded in the precast panels. The most extensive instrumentation program was completed by the University of Missouri for a PPCP project constructed on I-57 near Sikeston, Mo. (Luckenbill, 2009; Davis, 2006; Dailey, 2006).

2.3.2 Routine Inspection and Maintenance Because PCPS are significantly different from conventional concrete pavement, there are a number of aspects that should be routinely inspected over the life of the pavement. Routine project-level condition surveys should be conducted at least every 2 to 3 years to identify any new distress (listed in Sect. 2.3.3) or changes to existing distress. Expansion joints should be inspected at least every 1 to 2 years. Routine maintenance requirements for PCPS should be minimal. Expansion joints are a key element and must be properly maintained. The expansion joints should be inspected for buildup of debris in the joint, integrity of the joint seal, and for distress in the vicinity of the expansion joint that may indicate it is not functioning properly, such as spalls or cracking parallel to the joint. If significant buildup of dirt and debris is noted in the expansion joint (on top of the seal), it should be removed. If the seal has detached or is missing, the expansion joint should be cleared of any dirt and debris using compressed air, and the joint re-sealed. If header joints are used, the header material should be inspected for deterioration and delamination from the surrounding concrete. If armored expansion joints are used, the steel should be inspected for corrosion. If drains are provided at the ends of the expansion joints, these should also be inspected and cleared of blockage. Other routine maintenance may include sealing cracks that grow wider or deteriorate over time, and replacement or repair of any previously placed patches that show signs of deterioration.

2.3.3 Potential Distress The following is a list of possible distress that can occur in PCPS over the life of the pavement, with photos of typical distress shown in Figure 2.3.3-1. This list is not intended to be exhaustive as there is other concrete distress such as ASR found in conventional concrete pavement and structures that is discussed elsewhere (FHWA, 2005). Distress specific to production and handling of precast concrete elements are identified in the PCI Manual for the Evaluation and Repair of Precast Prestressed Concrete Bridge Products (PCI, 2006). Cracks―Cracks in PCPS may be transverse or longitudinal to the pavement centerline, corner cracks, or random cracks. Cracks that occur after installation may be caused by overloading or subgrade support issues. The cause of such cracking should be identified and action taken to address the main cause of the problem. Longitudinal cracking that spans several panels should be investigated in depth, particularly if the cracks occur directly above a post-tensioning tendon. Cracks in the anchor regions should also be examined carefully to ensure they are not due to or will result in anchor failure. Shrinkage cracks may also occur, but generally appear at the fabrication plant. Spalls―Spalls occur most often at joints between precast concrete panels, and normally occur during construction. If joints between panels are not closed or fully sealed with epoxy, there is the potential for 2 - 20

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incompressible material to fall into these joints and spall the edges of the joint over time. Spalls could also occur at expansion joints if the joints close completely or if the joint fills with incompressible material. Mid-panel spalling is unlikely, but may occur at cracks or if reinforcing steel is exposed. Joint Seal Deterioration―If joint seals are not installed properly, they may detach from the faces of the joint over time. If a poured silicone seal is used and is installed too high in the joint, the seal may “bulge” from the top of the pavement surface when the joints close due to warm temperatures. Stressing Pocket Distress―If the concrete material used to fill the stressing pockets is not placed properly, or if the material is not suitable for the application, the concrete may deteriorate and be ejected from the pockets under traffic. Also, if the pocket concrete is not cured properly or if the inner face of the pocket is not prepared properly, shrinkage cracks may occur around the perimeter of the pocket causing distress. Lifting Anchor Patch Deterioration―If the material used to patch the lifting anchor recesses is not installed properly, it may deteriorate and be ejected under traffic loading. Patch Deterioration―If the concrete for partial-depth patches (e.g., for repairing spalls) is not placed properly, or if the material is not suitable for the application, the concrete may deteriorate and come out of the patch area under traffic. If the patch is not cured properly or the inner face of the patch is not prepared properly, shrinkage cracks may occur around the perimeter of the pocket causing distress. Figure 2.3.3-1 Examples of Possible Distresses in PPCP

a) Transverse Panel Crack

b) Spall at Panel Joint

c) Expansion Joint Seal Deterioration

d) Cracking Around Perimeter of Stressing Pockets 2 - 21

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e) Lifting Anchor Patch Deterioration

2.3.4 Recommendations Concerning Repair Distress should be evaluated on a case-by-case basis to determine if it will affect pavement performance and if repair is needed. In general, minor distress occurring in the shoulders outside of the traffic lanes will not affect pavement performance and may not require repair. Even distress within the travel lanes may not require repair, and in fact, repairs could result in further problems. Below is a brief summary of recommendations for repair of certain kinds of distress. These are not intended to provide detailed repair procedures, but rather a summary of what actions might be taken. The PCI Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products (PCI, 2006) provides specific repair procedures for common distress or manufacturing defects in precast concrete elements. Cracks―In general, cracks in PCPS panels will be held tightly closed by prestress (for PPCP) and mild steel reinforcement (for JPPS) throughout the life of the pavement. However, if a crack appears to be active and growing , or if the crack begins to spall, repair may be necessary. The repair method will depend on the width and depth of the crack. In general, cracks should be sealed with methyl methacrylate, epoxy, or similar materials suitable for sealing and fully bonding cracks in concrete, rather than flexible bituminous or silicone materials. If the area of the crack is also severely spalled, the recommendations below should be followed. Spalls―Shallow surface spalls that can occur during construction are generally removed by the diamond grinding operation. However, deeper spalls may require partial depth repairs, particularly if they are located within the travel lanes. Partial-depth repairs involve cutting a clean perimeter around the spall area, removing the section of spalled concrete, patching it with a suitable patch material, and applying appropriate curing techniques. In general, partial-depth repairs should be at least 2 in. deep, but a deeper repair may be required for deeper spalls. Avoid 90 degree (or sharper) corners when saw-cutting the patch in order to avoid re-entrant cracks at the corners. Locations and depths of pretensioning and post-tensioning strands should be determined prior to beginning repairs to ensure the tendons are not disturbed. Joint Seal Repair―Joint seals that have detached from the joint face or are bulging from the pavement surface should be removed completely, the face of the joints cleaned, and the seal reinstalled. Stressing Pocket Repair―Stressing pocket deterioration may only occur at the surface of the pocket. If so, it may be necessary to perform only a partial-depth repair of the pocket. The partial-depth repair procedure described above should be used to initially evaluate whether 2 in. is deep enough, or whether additional depth should be removed. If necessary, additional depth can be removed and replaced. Extreme caution should be used when performing repairs in and near the stressing pockets to be sure the tendons and anchors are not disturbed. Lifting Anchor Patch Repair―Lifting anchor recesses should be repaired by fully removing the existing patch material, cleaning the recess, patching with a suitable patch material, and curing appropriately. If the old patch 2 - 22

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DESIGN AND MAINTENANCE OF PRECAST CONCRETE PAVEMENTS 2.4 Resources For Additional Information

material cannot be fully removed, it may be necessary to follow partial-depth patching procedures by enlarging the anchor recess slightly. Existing Patch Repair―Similar to the lifting anchor patch repair, the existing patch material should be fully removed and the patch recess cleaned, prior to installing new patch material. Enlarge the existing patch slightly if necessary if the old patch material cannot be fully removed. Stressing pockets should be checked for any noticeable distress that may indicate problems with the posttensioning anchorage and integrity of the concrete material used to patch the pockets. Joints between individual precast panels should be checked for the presence of spalls that may indicate stress concentrations at the joint. If new spalls are observed, they should be cleaned and repaired while shallow and small in area.

2.3.5 Functional Maintenance Functional maintenance encompasses all activities that ensure a smooth and safe pavement surface. Precast panels will likely require diamond grinding after installation to meet most ride quality standards for high speed roadways. Diamond grinding may not, however, be required for lower speed roadways such as ramps, intersections, and frontage roads. One advantage of PPCP over conventional jointed concrete pavement is the longer spacing between the active joints. Post-tensioned sections of PPCP tend to behave as a continuous pavement slab, reducing curling- and warping-related roughness for the 150- to 300-ft or more joint spacing, rather than the typical 15- to 20-ft joint spacing of conventional pavement. In terms of safety, the skid resistance of a diamond ground precast surface will be comparable to diamond ground conventional concrete pavement. If grinding is not anticipated (e.g., for a lower speed roadway), virtually any texture can be provided on the precast panels during fabrication, from basic turf drag texture, to tining, or even grooving. Precast panels typically receive a turf drag or broom finish during fabrication. This finish generally provides adequate pavement texture during construction and the early life of the pavement until diamond grinding is applied. If polishing of the pavement surface is a concern, harder, polish-resistant aggregates can be specified for the concrete mixture. Similar to conventional concrete pavement, precast panels may need to be diamond ground periodically over the life of the pavement to restore smoothness and texture for skid resistance. However, it is expected the intervals for this treatment should not be sooner than every 10 to 15 years.

2.4 RESOURCES FOR ADDITIONAL INFORMATION An online compilation of resources for additional information on precast concrete pavement has been assembled by PCI, and is available at the internet address below. This site will be continually updated as new information becomes available from current and future projects. www.precastconcretepavement.org

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DESIGN AND MAINTENANCE OF PRECAST CONCRETE PAVEMENTS 2.5 Cited References

2.5 CITED REFERENCES AASHTO. 2012. AASHTO LRFD Bridge Design Specifications, 6th Edition. American Association of State Highway and Transportation Officials, Washington, DC. 1672 pp. https://bookstore.transportation.org/collection_detail.aspx?ID=112 Cable, N. D., B. F. McCullough, and N. H. Burns. 1985. New Concepts in Prestressed Concrete Pavement. Research Report 401-2. Center for Transportation Research, University of Texas at Austin, Austin, TX. Dailey, Cody L. 2006. Instrumentation and Early Performance of an Innovative Prestressed Precast Pavement System. University of Missouri–Columbia. Columbia, MO., Master Thesis. Davis, Brent M. 2006. Evaluation of Prestress Losses in an Innovative Prestressed Precast Pavement System. University of Missouri–Columbia, Columbia, MO., Master Thesis. Dunn, M. J., M. D. LaViolette, D. K. Merritt, and S. S. Tyson. 2007. Precast Prestressed Concrete Pavement for Rapid Bridge Approach Slab Reconstruction, Proceedings, International Conference on Optimizing Paving Concrete Mixtures and Accelerated Concrete Pavement Construction and Rehabilitation, Atlanta, GA, November 7-9, pp. 347-360. FHWA. 2005. Distress Identification Guide. Report No. FHWA-RC-05-002. Federal Highway Administration LongTerm Pavement Performance Program, Washington, D.C., 60 pp. Luckenbill, G.C. 2009. Evaluation of the Service Performance of an Innovative Precast Prestressed Concrete Pavement, University of Missouri–Columbia, Columbia, MO., Master Thesis. Medina-Chavez, C.I., and M. Won. 2006. Long-Term Performance of Prestressed Concrete Pavement on IH-35 in Texas, In the Proceedings of the International Conference on Long-Life Concrete Pavements, October 25-27, Chicago, IL. Mendoza D., B. Alberto, F. McCullough, and N. H. Burns. 1986. Design of the Texas Prestressed Concrete Pavement Overlays in Cooke and McLennan Counties and Construction of the McLennan County Project. Research Report No. 555/556-1. Center for Transportation Research, University of Texas at Austin, Austin, TX. Merritt, D. K., B. F. McCullough, and N. H. Burns. 2002. Construction and Preliminary Monitoring of the Georgetown, Texas Precast Prestressed Concrete Pavement. Research Report No. 5-1517-01-1. Center for Transportation Research, University of Texas at Austin, Austin, TX. http://www.utexas.edu/research/ctr/pdf_reports/5_1517_1.pdf PCI. 2006. Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products, (MNL-137). Precast/Prestressed Concrete Institute, Chicago, IL. 72 pp. PCI. 2010. Design Handbook, 7th Edition, (MNL-120-10). Precast/Prestressed Concrete Institute, Chicago, IL. https://netforum.pci.org/eweb/dynamicpage.aspx?webcode=category&ptc_key=6ccabfe6-c4d9-4379-83b5d257a2bde354&ptc_code=Design%20Guides%20and%20Standards (Fee) PCI. 2011. Bridge Design Manual, Third Edition, (MNL-133-11). Precast/Prestressed Concrete Institute, Chicago, IL. 1,446 pp. https://netforum.pci.org/eweb/DynamicPage.aspx?Site=pci_nf&WebKey=636bf780-c237-4a1d-a7e4629fbef5ca94 (Fee) PTI. 2006. Post-Tensioning Manual, 6th Edition, (PTI TAB.1-06). Post-Tensioning Institute, Farmington Hills, MI. 354 pp. http://www.vbook.pub.com/doc/57832154/2011-Post-Tensioning-Institute-Publications-Catalog (Fee) Tayabji, S. D., E. J. Barenberg, W. Gramling, and P. Teng. 2001. Prestressed Concrete Pavement Technology Update, In the Proceedings of the 7th International Conference on Concrete Pavements. September 9-13, Orlando, FL. pp. 871-890. Tayabji, S. and D. Ye. 2010. Performance of Precast Concrete Pavements, In the Proceedings of the 7th International DUT-Workshop on Design and Performance of Sustainable and Durable Concrete Pavements, Carmona, Spain. 2 - 24

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.0 Introduction/3.1 Industry Quality Assurance

3.0 INTRODUCTION This third of four documents on the use of precast concrete pavement systems (PCPS), provides guidance for manufacturing the precast panels. Topics include quality assurance and fabrication tolerances; details of materials; formwork; fresh concrete handling, finishing and curing; unique fabrication procedures; the need for and types of repairs; and lifting, handling, and storage. The precast concrete industry will find this summary of experience from projects completed very helpful as a starting point for planning their involvement in upcoming work. Owner agencies will find these details useful in knowing how to deal with and evaluate their partnership with industry on their first PCPS project. In defining terminology, when PCPS are prestressed, either pretensioned in the fabrication plant, or posttensioned during construction, they are referred to as precast, prestressed concrete pavement or PPCP. Nonprestressed precast concrete panels are called jointed precast pavement systems, or JPPS. Some of the topics in this document on fabrication refer specifically to PPCP and other topics to JPPS. Other subjects can be applied to both systems. Generally, the topics and their applications are identified as they are discussed in the text.

3.1 INDUSTRY QUALITY ASSURANCE Since 1954, the Precast/Prestressed Concrete Institute (PCI) has generated and disseminated the technology, and has maintained the repository of the body of knowledge concerning precast concrete. Beginning in 1967, PCI led the construction industry in the development of innovative quality programs. With ever-increasing demand for improved quality, the certification of manufacturers, erectors, and personnel provides the customer the assurance that quality systems are being followed, personnel are qualified and control is practiced through each step of the construction process. Independent, unannounced audits help to ensure process control. The certification of a manufacturing plant by PCI ensures that the plant has developed and documented an in-depth, in-house quality system that is based on time-tested national industry standards. Production and quality standards are contained in the Manual for Quality Control for Plants and Production of Structural Precast Concrete Products, MNL-116 (PCI, 1999). This manual is recognized by the construction industry as the standard for the manufacture of precast and prestressed concrete since it was first printed in 1970. MNL-116 is the only such recognized national standard for the industry. The precast, prestressed concrete industry, through PCI, has taken bold steps to establish industry quality standards. The standards apply to personnel, to production and operations, to quality control, and to field operations. The standards have been published and widely disseminated and are open for evaluation and written comments, all of which are given consideration. The PCI industry standards for quality production are demanding to achieve. Once attained and practiced regularly, adherence to these standards contributes to improved and continuing customer satisfaction. Following these standards has been shown to reduce the “cost of quality” for the producer as well as the owner. Certification by PCI assures compliance to the published standards for quality production. Certified personnel and producers choose to demonstrate their proficiency by voluntarily undergoing examinations and audits by accredited third-party assessors. PCI Plant and Personnel Certification are reliable means for qualifying personnel and precast concrete producers.

3.1.1 Fundamentals of PCI Plant Certification Every PCI-Certified plant is audited twice each year. These audits are not announced in advance. Auditors are independent, specially trained, and accredited engineers. They are employed by a single consulting engineering firm under contract to PCI, which ensures consistency for every plant. Every audit ends with a closing meeting. Auditors and key plant personnel meet to review preliminary results. If improvements are needed, they can be started right away. Later, a detailed written analysis documents observations and reasons for required improvements. The report also includes a numerical grade sheet that indicates the level of compliance with the standards.

3-1

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Nonconformances contained in the written report require an immediate response. The plant’s plan to mitigate the issue must be stated. Such measures will be reviewed at the subsequent audit. If the numerical grade falls below specific criteria, the plant must undergo an immediate special audit. Failure to comply with standards will result in decertification.

3.1.2 Quality Personnel Certification Conducting an effective quality control program requires knowledgeable and motivated testing and inspection personnel. Each must understand quality basics, the necessity for quality control, how products are manufactured, and precisely how to conduct tests and inspections. PCI has been training quality control personnel since 1974. There are three levels of Plant Quality Personnel Certification. PCI Plant Certification requires appropriate levels of certification for personnel.

3.1.3 Qualified Fabricators PCPS panels are a unique product type and application. It is recommended that they be produced only by established PCI-certified plants qualified for this category of products. PCPS panels fall within PCI certification product group “B,” bridge-related precast concrete products. This group encompasses all products specified by owner agencies for highway and bridge projects. In Group B, nonprestressed panels are in category B1 (Precast Bridge Products) and prestressed panels fall in category B2 (Prestressed Miscellaneous Bridge Products) or B3 (Prestressed Straight-Strand Bridge Members). Panels should not be produced in temporary fabrication plants set up near a project site, unless the temporary plant is certified by PCI in the United States. Qualifications for producing pavement panels include experience with pretensioned flatwork and experience with embedding post-tensioning hardware in precast products. In addition, plants producing PPCP panels should have experience with highway projects specified by public agencies and those agencies’ typical in-plant quality assurance practices.

3.1.4 The Plant Quality System Manual PCI Plant Certification is a process for quality improvement, ensuring that a precast concrete fabrication plant is operating within industry-established and proven standard practices for production and quality control of precast concrete products. PCI Plant Certification requires that a fabrication plant document unique methods in their custom Quality Systems Manual (QSM). The specific content of a QSM is defined in Division 1 and Appendix A of MNL-116. There must be fifteen separate sections that define all operations in the plant. Each QSM must be approved by PCI prior to certification and must then be reviewed annually by plant management and updated when necessary. The QSM defines all practices and procedures that affect the quality of the finished product. In addition to a defined detailed program of quality control to monitor production by compliance with acceptable industry standards, the QSM defines all steps in the production process, identifies responsible persons, how materials are purchased and accepted, how products are identified and stored, and all other facets of manufacturing. The QSM must include the procedures for production and control of precast concrete pavement panels based on project specifications requirements and industry recommended practices. The owner agency should require submittal of the relevant sections of the manufacturer’s QSM that deal with production and quality control of the pavement panels.

3.2 TOLERANCES Tolerances provide for the dimensional control of precast concrete products and construction. Projects using precast pavement panels must be successful from all points of view, namely, owner satisfaction, ontime schedule performance, economy, aesthetics, constructability, and long-term functional durability. It is essential that the members of the project team collaborate to provide an overall project tolerance system that will meet all of the project’s functional needs and allow the most economical fabrication and construction. The tolerances presented in this document provide a suggested reference point. Each of these tolerances was set based on current modern precast concrete production techniques and experience gained from projects using precast pavement panels. They are based on a standard of quality and craftsmanship that can be reliably accomplished by a PCI-certified producer. These tolerances are not intended to be an unyielding and rigid set of 3-2

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tolerances used only as a measure for acceptance or rejection. Instead, they should provide both a feasible and economically reasonable set of starting tolerances that will enable the party responsible for tolerances to develop a successful project tolerance plan. Two sets of tolerances are necessary for a successful project:  

Product Tolerances―Product tolerances are defined as those tolerances related to the dimensions and dimensional relationships of the individual precast concrete members. Product tolerances are provided in this document. Erection Tolerances―Erection tolerances are defined as those tolerances that are required for the acceptable matching of the precast members after they are erected. Erection tolerances are presented in Document 4.

The tolerances shown in this document are guidelines for acceptability. Many projects involve situations that require variation from the published tolerances. Only the recognized and agreed upon “project tolerances” govern the production of the precast members. Not all tolerances are critical in every case, particularly when the structural performance is not impaired. In some circumstances, the engineer may accept an out-of-tolerance member if it conforms to any of the following:   

Exceeding the project tolerances does not affect the structural integrity or field fit of the member. Often the input of the Engineer of Record is necessary to evaluate the consequences of out-oftolerance situations. The member can be brought within project tolerance by structurally satisfactory means. Repair methods used to correct tolerance problems should not compromise structural performance or materially affect long-term durability. The total erected assembly can be modified to meet all structural requirements.

Modification of installation activities to accommodate out-of-tolerance members requires close coordination between the producer’s representative and the contractor. The effects of prestressing can have an effect on member dimensions and should be considered in the plan to meet specified tolerances. The producer should assure that the effects of prestressing have been accounted for in determining the form setup dimensions for member casting. Axial shortening of the member as result of the applied axial compressive force of the prestress is one effect. Another is camber due to eccentricity in a panel with a variable thickness. Solar heating of members stacked in the precasting yard or jobsite may cause camber variations due to differential temperature. Because of this it may be important to measure camber in the panels at times when thermal effects are minimal. Accurate measuring devices and methods with the precision appropriate to the tolerance being considered should be used for checking product and erection tolerances. Typically, the precision of the measuring technique used to verify a dimension, either pre- or post-casting, should be capable of reliably measuring to a precision of one-third the magnitude of the specified tolerance.

3.2.1 Finished Product Tolerances Fabrication tolerances for PPCP panels are critical for ensuring that the panels will fit together properly when assembled on site, and that the finished pavement surface will have an acceptable ride quality. The most important tolerances include those for the shape and straightness of the keyed panel joints, evenness of the surface, thickness, squareness, and locations of. PPCP panels are typically not match cast so keyway tolerances are especially important. Maintaining proper tolerances will help to ensure that the joints between panels are close fitting, will be water-proof, and that there is very little, if any, deviation in vertical alignment between adjacent panels. Keyway dimensions are specified to provide tolerance in the fit of mating keyways to accommodate minor imperfections in formwork. It is important that there is no point contact of the surfaces in the keyway joint because spalls are likely to occur during the posttensioning operation that will clamp the joints together during installation. In general, tolerances of ±1/16 in. are achievable using properly designed and constructed formwork (described in Sect. 3.2.4). Tolerances for panel thickness are necessary to ensure satisfactory ride quality of the finished pavement surface. A thickness tolerance of ±⅛ in. is common, which will generally result in no more than ¼-in. vertical differential 3-3

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between adjacent panels. While ¼-in. deviation is not desirable in terms of smoothness for a pavement surface, it can be ground with a single pass of a diamond grinding machine to bring the pavement surface within typical smoothness standards. Tolerances on overall dimensions are important to ensure that panels fit where they are intended to be installed. This is particularly important for reconstruction projects, where PCPS must be installed in a confined excavation where the existing pavement was removed. Tolerances for overall dimensions are also important for ensuring the pavement does not “grow” or “shrink” in length (finished pavement shorter or longer than designed) or alignment (curve or sweep in pavement that deviates from the intended alignment). A tolerance of ±⅛ in. is generally specified for overall panel width (i.e., same direction as the length of the actual pavement) and for overall length (i.e., same direction as the width of the actual pavement). The tolerance for squareness, which is measured diagonally across the top surface of the panel from corner to corner, is generally specified to be no greater than ±⅛ in. from the calculated plan dimension. Other overall dimensional tolerances include those for mating edge straightness and vertical batter at the edges of the panel, as defined in Figure 3.2.1-1. Table 3.2.1-1 provides dimensional tolerances for PPCP panels. Tolerances for JPPS are listed in Section 3.10.2.2. Figure 3.2.1-1 Definition of Dimensional Tolerances

Squ

aren ess

Width

Length

Mating Edge Straightness (Edge Bow)

Mating Edge Straightness (Vertical Camber)

ess aren

Squ

Nominal Thickness

Vertical Batter

Profile

Plan

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Table 3.2.1-1 Dimensional Tolerances Length and Width Nominal Thickness Squareness―difference from calculated plan dimension (measured diagonally from corner to corner across top surface) Mating edge straightness (upon release of stress)―Deviation from straightness of mating edge of panels Vertical batter (edge squareness) along transverse joint faces and ends of panels

±⅛ in. ±⅛ in. ±⅛ in. ±⅛ in. ±⅛ in.

3.2.2 Tolerances for Reinforcement and Embedments This section describes the tolerances for location of reinforcement and embedments including: pretensioning strands, post-tensioning ducts, nonprestressed reinforcement, panel lifting devices, and blockouts or holes in the panels. The tolerance for location of pretensioning strands is important for ensuring adequate concrete cover and to prevent any unintended eccentricity, either vertical or horizontal. Pretensioning strands are generally held in place by passing them through drilled bulkheads at both ends of the precast panel providing very accurate positioning. A tolerance of ±⅛ in. vertically and ±¼ in. horizontally is generally specified for pretensioning strands, as shown below in Table 3.2.2-1. The straightness of post-tensioning ducts is important for minimizing “wobble” frictional losses during tensioning of the tendons. Positioning of the ends of the ducts at the panel joints is especially important to ensure that ducts align between panels. A tolerance of ±¼ in. per 10 ft of length is generally specified for straightness, both horizontally and vertically, and ±⅛ in. for the position of the ducts at the surface of mating edges. Tolerances for other reinforcement and embedments include those for lifting anchors, blockouts, post-tensioning anchors, and nonprestressed reinforcement. In general, greater tolerance is permitted for locating lifting anchors so they can be positioned as necessary to avoid conflicts with other embedments and reinforcement. Tolerances for blockouts include the location and dimensions of the blockouts, and are generally ±⅛ in. for blockout dimensions and ±¼ in. for position. Table 3.2.2-1 Tolerances for Reinforcement and Embedments ±⅛ in. Vertical1 ±¼ in. Horizontal ±⅛ in. Vertical1 ±⅛ in. Horizontal ±¼ in. Vertical1 ±¼ in. Horizontal ±3 in.2

Position of Strands Position of post-tensioning ducts at mating edges Straightness of post-tensioning ducts (per 10 ft) Position of lifting devices Position of nonprestressed reinforcement, including tie-bars Dimensions of blockouts/pockets 1 Measured from bottom of panel 2 From position shown on panel shop drawings 3 Unless different tolerance shown in plans

±¼ in.3 ±⅛ in.

3.2.3 Expansion Joints The tolerances of concern for expansion joints (cast into joint panels) are straightness, initial width of the joint opening, and dowel bar placement, as shown in Table 3.2.3-1, below. A tolerance of ±⅛ in. is generally specified for straightness and initial width. Note that the initial width tolerance should be applied to the set-up of initial 3-5

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.2 Tolerances

width along the length of the joint. The width of the expansion joint may not be uniform after post-tensioning, but it should be within this tolerance when shipped from the fabrication plant. For dowel bars cast into the panels, horizontal and vertical alignment tolerance is generally specified as ±⅛ in. For dowel location, a tolerance of ±¼ in. from the plan location in both the horizontal and vertical location is normally specified. For dowel embedment on both sides of the expansion joint, ±1 in. tolerance is adequate. Table 3.2.3-1 Tolerances for Expansion Joints Vertical Dowel Alignment (parallel to bottom of panel) Horizontal Dowel Alignment (normal to expansion joint)

±⅛ in. 1 ±⅛ in. ±¼ in. Vertical1 ±¼ in. Horizontal ±1 in. ±⅛ in. ±⅛ in. ±⅛ in.

Dowel Location (deviation from shop drawings) Dowel Embedment (in both sides of expansion joint) Straightness of expansion joints Initial width of expansion joints Dimensions of blockouts/pockets 1 Measured from bottom of panel

3.2.4 Formwork Proper formwork is the key to ensuring that overall panel dimensional and keyway tolerances are achieved. They must be rigid enough to prevent bending, bowing or sagging when fresh concrete is placed in the forms and consolidated, and must be rugged enough for repeated use without deformation or damage. The forms must also be securely fastened in place to ensure they will not move when the pretensioning strands are tensioned or when fresh concrete is placed. Experience has shown that heavy-duty steel formwork shown in Figure 3.2.4-1 provides the best material for ensuring that PPCP panel tolerances are achieved, particularly for the non-match cast keyway joints. Steel formwork is less susceptible to warping, will not swell, and can be re-used virtually any number of times as long as it is properly maintained. While wooden formwork may also be fabricated to the required tolerances, it is not recommended for projects when the formwork must be re-used repeatedly. For these larger projects, wooden forms will likely need to be replaced partway through production, increasing the possibility of variances in panel dimensions, particularly keyways. The tolerances to which the forms are made and the tolerances to which they can reliably be adjusted are an important determinant of the ability to achieve specified member tolerances. The proportion of the product tolerance variation that results from form fabrication tolerances or adjustment precision should be considered in the plan to achieve specified member tolerances. One of the most important considerations that should be taken into account in the selection of the types of forms to be used is the precision of dimensional tolerance specified for the member. As a rule of thumb, forms should be manufactured to tolerances of one-half the allowable dimensional tolerances for the product.

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Figure 3.2.4-1 Heavy-duty Steel Formwork used for PPCP Panel Fabrication

a) Side and Tongue Form (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Transverse End Form and Surface Form

3.3 MATERIALS 3.3.1 Concrete 3.3.1.1 Strength The typical strength of mixtures used in precast, prestressed concrete products will be more than adequate for concrete pavement. Typical compressive strength requirements for PPCP are 3,500 to 4,000 psi at transfer of prestress, and 5,000 to 6,000 psi at 28 days. Mixtures should not be “over-designed” to achieve higher than necessary strength. High strength concrete is not necessarily advantageous for pavement slabs, and in fact may have adverse effects on pavement performance due to the higher modulus of elasticity. It is also more difficult to finish. 3.3.1.2 Durability Mixtures for PPCP panels should be selected to satisfy the durability requirements for both precast concrete elements as well as portland cement concrete pavement exposed to the conditions anticipated for the project. Standard specification requirements for both types of construction (precast concrete and concrete pavement) should be reviewed to determine which requirements will govern for PPCP. Because the panels are installed on grade, they should meet requirements for concrete permanently exposed to earth. Other important durability requirements include low permeability for protection of prestressing steel and nonprestressed reinforcement, and adequate air content for freeze-thaw resistance. 3.3.1.3 Aggregates Aggregate requirements affect durability as well as pavement performance, and are governed more by concrete pavement specifications than precast concrete specifications. Durable, nonreactive aggregates are important because, depending on location, pavement slabs are subjected to continual wetting and drying cycles, freeze-thaw cycles, and exposure to de-icing salts. Aggregates should not be susceptible to alkali-silica reactivity or D-cracking. Concrete with a lower coefficient of thermal expansion (CTE), which is primarily dictated by the CTE of the aggregate, is generally more desirable, as CTE directly affects slab movement under daily and seasonal temperature cycles. Less slab movement will reduce expansion joint movement and slab-base frictional restraint stresses. Therefore, if a precast plant typically uses a high CTE aggregate (e.g., 6-9 µε/ºF), a lower CTE aggregate (e.g., 2-5 µε/ºF) may need to be obtained for production of PPCP panels. 3-7

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Functional performance is also affected by aggregate properties. Pavement friction is highly dependent upon the abrasion and polish resistance of the coarse and fine aggregates in the concrete mixture. As such, the agency may require aggregates that are more resistant to abrasion and polishing for PPCP panels, similar to those typically used for pavement aggregates. If aggregates commonly used in a particular plant for precast elements are deemed not suitable for a pavement surface, aggregate with better abrasion resistance may need to be obtained for PPCP panel production.

3.3.2 Prestressing Steel Prestressing steel should conform to standard requirements for highway applications. For use in pretensioning, ½-in.-diameter, low-relaxation, Grade 270, seven-wire strand is typically used for PPCP panels. It provides the necessary prestress with 6 to 8 strands per panel. Larger (e.g., 0.6-in.- or 0.7-in.-diameter) or higher strength (e.g., Grade 300) strand could be used, thereby decreasing the number of strands required, but will result in an increase of the prestress transfer length from the edge of the precast panels. Even smaller diameter (e.g., 7/16-in. or ⅜-in.) strand should be considered for shorter precast panels in order to further reduce the prestress transfer length. Epoxy-coated prestressing strand can be used for pavements to be constructed in a particularly aggressive environment. In addition, they would require less concrete cover. Grit-impregnated epoxy-coated strand is available and will reduce the transfer length more than bare strand, but at an additional cost. Epoxy-coated strand should be specified as “epoxy-filled, epoxy-coated” strand to ensure the interstices between the individual wires of the strand are also filled with epoxy. Epoxy-coated strands have not been previously used for PPCP pretensioning but have been used in several projects for post-tensioning tendons.

3.3.3 Nonprestressed Reinforcement With the exception of reinforcement in joint panels and central stressing panels, the amount of nonprestressed reinforcement in PPCP panels for most applications is minimal. Prestressing is normally designed to reduce tensile stresses in the panels so that nonprestressed reinforcement for handling purposes is not necessary. However, a minimal amount of nonprestressed “shrinkage and temperature” reinforcement is generally provided normal to the pretensioning to account for shrinkage and thermal stresses that the panels may encounter prior to installation and post-tensioning. A potential reduction of cost might result from the use of welded-wire reinforcement (WWR). WWR mats are factory fabricated with custom amounts of reinforcement (wire and spacing) in both directions. The mats can be trimmed around embedded hardware as necessary and then simply laid in place in the forms without the need for labor to tie the individual bars at intersections. Additional nonprestressed reinforcement in joint panels includes bursting steel at post-tensioning anchors, and stirrups added to transfer the prestress force from the post-tensioning anchors back to the expansion joint. In central stressing panels, it includes reinforcement around the stressing pockets to arrest cracks that may form at the corners of the pockets. All nonprestressed reinforcement should conform to standard requirements for concrete pavement reinforcement for the location where it will be constructed. In general, reinforcement must have the minimum required concrete cover in accordance with the AASHTO LRFD Specifications, Article 5.12.3 (AASHTO, 2012). Epoxy-coated, galvanized, or stainless steel reinforcement is recommended, particularly if the pavement is to be constructed in an aggressive environment.

3.3.4 Post-Tensioning Materials 3.3.4.1 Tendons Seven-wire strands are typically used for PPCP post-tensioning. These strands are manageable in the field and provide the necessary prestress using single strand tendons spaced from 2 to 3 ft apart. Epoxy-coated posttensioning strands have been used successfully for projects constructed in aggressive environments. The epoxy coating adds only approximately 0.05 in. to the nominal diameter of 0.6-in-diameter strand, so a larger duct is not required.

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An alternative or supplement to strand tendons is bar tendons. High-strength (Grade 150) threaded bars are commonly used for post-tensioning in other applications. Bar tendons may be cast into or inserted into ducts on site in each individual panel to allow the panels to be “sequentially” assembled by coupling the bar tendons for each panel to the tendons in the previous panel. This permits the contractor to terminate each day’s installation at any location, while ensuring an adequate level of post-tensioning force to compress the joints in the pavement between installations. Bar tendons can be used for all of the post-tensioning tendons, or to replace two or more strand tendons. On some of the projects completed to date, two bar tendons were used as the temporary posttensioning, replacing two of the strand tendons in each panel. Bar tendons will require larger post-tensioning ducts than strand tendons, particularly when couplers are used. As with strand tendons, epoxy-coated bar tendons are available for use in aggressive environments, and increase the diameter of the bar by only approximately 0.05 in. 3.3.4.2 Ducts, Anchors, and Grout Ports Specific post-tensioning materials are typically not specified on the project plans, requiring the contractor or precast fabricator to select the materials. Post-tensioning ducts and anchors should be selected based on the type of tendon and environment where the pavement will be constructed. The ducts must be large enough to accommodate the tendons and, if bar tendons are used, the bar couplers. Ducts should be compatible with the anchors at the ends of the tendons. Assuming bonded tendons, the ducts must provide for grout ports. Consideration should also be given to corrosion resistance of the duct, the flowability of grout through the duct, and rigidity to maintain position during fabrication and concrete placement. Post-tensioning ducts, as shown in Figure 3.3.4.2-1, should be either rigid plastic (polyethylene or polypropylene) specifically manufactured for post-tensioning applications, or galvanized steel. All ductwork should be sufficiently watertight to prevent concrete mortar from seeping into the ducts during fabrication. This is particularly critical at grout ports that are spliced into a duct, and around the joints between a duct and the anchor. Galvanized steel ducts are more rigid than plastic ducts, requiring less chairing in the forms, but are susceptible to corrosion in aggressive environments over time (Salas et al., 2002). The method to support plastic ducts should be reviewed for rigidity to prevent displacement during concrete placement. Some fabricators have used dowels through the ducts attached to the side forms that are removed when the panels are stripped from the forms. When selecting duct material, consideration should be given to availability of duct couplers to provide a watertight seal between duct segments across the joints between panels. Duct couplers should be used whenever possible to reduce grout leakage at the panel joints and to protect the post-tensioning tendons from ingress of contaminated water. At this writing, duct couplers for single strand post-tensioning ducts are reported to be in the final stages of development. Tendon anchors should be compatible with the duct material so that a watertight seal is provided between the duct and anchor. Fully encapsulated anchor systems should be used to minimize the risk of corrosion of and inside the anchor, particularly for projects constructed in aggressive environments. Various anchor configurations that have been used previously are shown in Figure 3.3.4.2-2. Post-Tensioning duct grout ports are typically located just in front of post-tensioning anchors, on both sides of any stressing pockets, and at 40- to 50-ft intervals along the duct. Grout ports are typically vented to the surface of the precast panels. They can be recessed slightly (½ in. or less) from the surface to accommodate screeding, but should be uncovered as soon as possible after surface finishing is complete. Methods must be used to disturb the finished surface of the panel as little as possible during this procedure. Fittings such as tees for grout ports should be compatible with the duct material and a watertight seal should be provided between the duct and fitting, as shown in Figure 3.3.4.2-3.

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Figure 3.3.4.2-1 Post-tensioning Duct Materials

a) Galvanized Metal Spiral Duct

b) Both Plastic and Galvanized Metal Ducts

c) Rigid Plastic Single-Strand Duct Figure 3.3.4.2-2 Examples of Post-Tensioning End Anchorage Assemblies

a) Fully Encapsulated Anchor

b) Manufactured Anchor 3 - 10

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c) Two-strand Anchorage (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

d) Spring-loaded Encapsulated Anchor (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

Figure 3.3.4.2-3 Mid-panel Grout Vents used with Plastic Ducts

a) Ribbed Plastic Duct

b) Smooth Plastic Duct (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

3.3.5 Post-Tensioning Pockets Pockets for tensioning the post-tensioning tendons are cast into the joint panels and central stressing panels. The blockouts can be formed with wood, which is sacrificial, or steel, which is reusable, as shown in Figure 3.3.5-1. Both materials should have draft (slope) on their sides to permit them to be removed from the cured concrete panel. Blockout formers are generally recessed slightly from the surface of the panel to accommodate screeding and finishing. Reusable blockout forms can be wrapped with a thin (i.e., less than ¼ in. thick) sheet of sacrificial closed-cell polystyrene foam to allow them to be removed following curing. Blockouts should have rounded corners of approximately 1 in.-radius, or as shown on the plans, to reduce the risk of reentrant cracks in the concrete.

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.4 Prestressing

Figure 3.3.5-1 Types of Forms used for Stressing Pockets

a) Steel Form Wrapped with Thin Layer of Foam (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) One-time-use Wood Form

c) Steel forms with Drafted Sides and Lids to Prevent Filling during Concrete Placement

3.4 PRESTRESSING 3.4.1 Placement of Strands PPCP panels should be designed to utilize the maximum allowable jacking force in the pretensioning strands in order to minimize the total number needed. The location of the strands should result in concentric prestress force as much as possible, which will typically require strands to be alternated above and below the post-tensioning ducts that are normal to the pretensioning strands. Planning strand layout should seek to minimize the number of pretensioning strand patterns for a particular project. Ideally, for panels with the same dimensions, only 1 or 2 strand patterns should be necessary to accommodate all typical, joint, and stressing panels. Pretensioning strands may be harped (deviated from a straight line) slightly if the panel has a variable thickness or sloping top surface. Some examples of deflection methods are shown in Figure 3.4.1-1. Stiff steel bulkheads can be bolted to the bottom (soffit) form and used as deflection points. Strong bar chairs can also be used to support the strands from the bottom at deflection points within the panels. 3 - 12

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.4 Prestressing

Figure 3.4.1-1 The Trajectory of Prestressing Strands may be Deviated in the Forms

a) Steel Bulkheads between Panels used to Deflect Pretensioning Strands

b) Steel Chairs used to Support Pretensioning Strands at Deflection Points

3.4.2 Placement of Ducts and Anchors Post-tensioning ducts should be adequately fixed in the forms to prevent bowing, sagging, or floating during concrete placement. Plastic ducts that are more flexible will need to be supported with chairs at 3 or 4 locations across a 10-ft-wide panel. Some methods are illustrated in Figure 3.4.2-1. Temporary steel stiffeners (e.g., dowels or rods) should also be inserted in the ducts during concrete placement to minimize floating, bowing, or sagging from the weight and buoyancy of the fresh concrete. To ensure that the ducts will align between panels, the side forms should be drilled at the duct locations to help hold the duct in place at the planned location. Post-tensioning anchors that are embedded in the panels should be securely bolted to the formwork or blockout formers. Anchors should be properly secured in place so that they do not shift or rotate when concrete is placed and vibration used for consolidation. Bursting steel reinforcement should also be held securely in place in front of the anchors. Blockout formers should be securely fastened to the bottom form so that they do not shift or float during concrete placement. Figure 3.4.2-1 Post-tensioning Ducts must be Held Rigidly in Place in the Forms

a) Plastic Ducts Supported with Multiple Chairs

b) Rigid Metal Ducts Supported between Pretensioning Strands

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.5 Expansion Joint Panels

3.4.3 Transfer of Prestress The transfer, or release, of prestress, should follow standard industry procedures. The transfer of prestress to the concrete is usually accomplished by cutting the strands with an oxy-acetylene torch just outside the bulk heads and end forms. The fabricator should use the procedures that are most familiar. For flame release, detensioning generally starts with strands at the outer edges of the panels, alternating to opposite sides of centerline and working toward the center. Because there are usually 6 to 8 pretensioning strands in each panel, prestress levels are much smaller than those in bridge girders and similar products. The prestress force should be transferred to the concrete as soon as possible after the required concrete strength has been achieved. This will help to prevent transverse cracks (perpendicular to the direction of prestress) from occurring. Such cracking is due to shrinkage of the concrete and restraint from the tensioned strands during thermal contraction that follows the heat of cement hydration and any external heat from accelerated curing.

3.5 EXPANSION JOINT PANELS Plain dowelled joints are most commonly used with PPCP. However, armored joints and header-type joints, described in Document Two, are other options. Creating the expansion joints in the joint panels can significantly add to formwork setup time and complexity, as illustrated in Figure 3.5-1. The most critical aspects of forming the expansion joints include dowel bar placement and alignment, initial joint width, and preventing the two halves of the joint panels from locking together. For plain dowelled joints, the dowel bars are typically held in place by a temporary form used within the center of the expansion joint. The dowel bars must be held securely in place to the alignment tolerances specified in the plans. After one half of the joint panel is cast, the temporary middle form is removed, leaving the dowels protruding from the expansion joint (Fig. 3.5-1 c). Then, the other half of the joint panel is cast. If an initial width of opening is not specified for the expansion joint, the second half may be cast against the first half. However, it is critical that a bond breaker is applied to the exposed face of the expansion joint to prevent the two halves from bonding to each other. If an initial joint width is required, it can be formed by using plywood or polystyrene within the joint prior to casting the second half of the panel. Armored joints generally consist of a pre-modularized steel structure that is set in the forms as a single unit (Fig. 3.5-1 a). It includes the joint seal receiver extrusion, anchor bars or studs to anchor the seal extrusion to the panel, and dowel bars and dowel bar expansion sleeves. The two halves of the armored joint are typically tack welded together to maintain alignment. The initial joint width can be set by welding temporary shim plates between the two halves of the joint. These will be removed once the joint panel is installed. Armored joints should be carefully checked for straightness. The steel seal receivers tend to bow when welded on. As with plain dowelled joints, it is critical to hold the dowel bars securely in place to ensure they are within tolerance for alignment. Header-type joints are formed similarly to plain dowelled joints. The exception is additional formwork to create the recess for the header material along the top of the joint. This recess-former is typically attached to the temporary side form used to form the face of the joint (Fig. 3.5-1 b). Regardless of the type of expansion joint used, the dowel bars must be held securely in place to the tolerances specified. Misaligned dowel bars may lock the two halves of the joint panel together, preventing them from opening properly in place. Additionally, the dowel bars must be greased along the full length of the dowel bar to prevent them from bonding to the concrete and locking the expansion joint. Greasing the dowels should be completed just prior to concrete placement. White lithium or similar grease should be used, not just form oil or curing compound.

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Figure 3.5-1 Fabricating Expansion Joint Panels (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

a) Armored Expansion Joint

b) First of Two Halves of a Header-type Joint

c) Second Half of a Plain Dowelled Joint Set Up to Cast

3.6 CONCRETE PLACEMENT, FINISHING, AND CURING The tops of PPCP panels serve as the finished riding surface of the pavement. Therefore, concrete placement, finishing, and curing are especially important aspects of panel fabrication. Further, these procedures can have significant effects on long-term pavement performance and should be carefully controlled for that reason as well.

3.6.1 Concrete Placement 3.6.1.1 Protection of Embedments Adequate protection must be provided for embedded items in the precast panels during concrete placement to prevent them from moving due to pressure of concrete flow or from the vibrators used to consolidate the concrete, as shown in Figure 3.6.1.1-1. This includes post-tensioning ducts and hardware, post-tensioning blockouts, the expansion joints, lifting anchors, and reinforcement. All embedded items should be securely tied in place or bolted to the formwork whenever possible. Blockout formers should be monitored to ensure they do not shift or leak (fill with mortar), and reinforcement should be checked to ensure specified concrete cover. Reinforcement too close to the surface will be susceptible to corrosion or even exposed during diamond grinding of the surface. Post-tensioning ducts should be monitored for floating, bowing, or sagging under the force of concrete flow. Placing the concrete in two “lifts” has been shown to be very effective to prevent ducts from sagging or bowing. The first lift fills the panel forms to approximately the level of the ducts. The second lift, placed immediately after the first, fills the forms to the top (see Fig. 3.6.1.1-1). It is important that the second lift be placed soon after the first so that a cold joint is not formed between the two lifts.

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Figure 3.6.1.1-1 Fabrication and Concrete Placement Techniques

a) Internal Vibrators (Stingers) being used to Consolidate Concrete around Well-anchored Blockout Formers (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) The Second Lift of Concrete is shown being Placed in a Two-lift Production Sequence (Photo: R. Jon Grafton)

3.6.1.2 Consolidation Concrete should be vibrated to consolidate it into edges, corners, and around embedments, but should not be over-vibrated resulting in segregation. Segregation of the mixture will result in a variable water/cementitious materials ratio and leave mortar and fine aggregates at the top surface of the panels. That will reduce durability and abrasion resistance. Flowing concrete mixes or self-consolidating concrete, which require minimal or no vibration to consolidate, have been shown to work very well for precast pavement panels. However, these mixes will not work as well for panels with a variable thickness as shown in Figure 3.6.1.2-1. For variable thickness panels, the fresh concrete must be stiff enough to resist the tendency to flow “downhill” from the high point in the formwork. The concrete should not be so stiff that the surface is difficult to finish or that honeycombing might occur in the panel. Figure 3.6.1.2-1 PPCP Panels Fabricated for Two Projects with Variable Thickness

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3.6.2 Screeding, Finishing and Texturing Precast pavement panels are generally screeded to the top of the side forms, providing a very uniform surface. Vibratory screeds and roller screeds have been shown to provide a uniform surface that requires minimal hand finishing. Both types of screeds must be carefully monitored and properly weighted to ensure that they do not “ride up” on the fresh concrete, resulting in an irregular panel surface. Screeding is aided by minimizing the number of protrusions from the top surface of the panel, including lifting anchors, grout vents, and blockout formers. Whenever possible, embedments should be secured to the bottom form or side forms to minimize or eliminate the use of hold-downs penetrating the surface by resting on the tops of the side forms. Sacrificial wood covers should be used to cover open blockout formers, and foam plugs must be used in grout ports. Lifting anchors that rest on the bottom of the form are available to eliminate the need to suspend or support the anchors through the top surface. Only minimal hand finishing should be required after screeding, but additional hand finishing may be required around expansion joints, post-tensioning blockouts, lifting anchors, and grout ports. After screeding, a texture is typically applied in the long direction of the panels (transverse to the direction of traffic) using a turf carpet drag or broom. Some agencies may require a tined finish either in the long or short direction of the panel. Some textures and application procedures are shown in Figure 3.6.2-1. Regardless of the texturing method, care must be taken to prevent tearing the surface or turning up aggregates. If the pavement surface is to be diamond ground after the panels are installed, only a medium broom finish or carpet drag may be necessary for “short term” use as diamond grinding will provide the final surface texture. During the finishing and texturing procedures, “intermediate” curing compounds or evaporation reducers can be applied to the surface to retard surface moisture loss prior to final curing. Additional water should not be used to aid finishing of the surface as this may lead to scaling after the concrete has cured. Final curing should be applied as soon as possible after texturing.

Figure 3.6.2-1 Panel Surface Textures

a) A Section of Artificial Turf is being Drug to Impart a Longitudinal Finish (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) A Specially Fabricated Bristle Broom the Full Width of the Panel Applies a Longitudinal Finish

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c) A Jig with Tines was used to Apply a Longitudinal Finish

d) Applying a Transverse Broom Texture

3.6.3 Curing Curing precast concrete pavement panels is an important procedure due to the large exposed surface area. Shrinkage cracks before or during curing may be cause for rejection because these cracks could be a point of ingress for chlorides and significantly affect long-term pavement performance. Many precast plants use the application of heat to accelerate curing. This allows the concrete to attain the required release strength within a matter of hours after concrete placement. Radiant heat can be supplied through pipes circulating hot liquids. Some fabricators vent steam in the spaces surrounding the concrete. In some cases, concrete mixtures containing Type III portland cement have been used successfully without the need for supplemental heat. For panels that are not exposed to steam, including those using radiant heat curing, a thick (i.e., two coats) application of curing compound should be applied to the panel surface as soon as possible after texturing to prevent surface evaporation of moisture. If any part of the formwork is removed during the curing process (for non-steam-cured panels), the exposed surface of the precast panel should receive a thick application of curing compound or be covered with plastic sheeting or wet mats. Various curing techniques used for PPCP panels are shown in Figure 3.6.3-1. Curing of the concrete in the forms is required until the panels achieve prestress transfer strength. Upon removal from the forms, additional curing may be required by the owner agency until the 28-day design compressive strength is achieved (which may be in as few as 24 to 72 hours after the panels are removed from the forms). The curing in storage includes the tops and sides of the precast panels. Curing can use membranes (curing compound), plastic sheets, or wet mats. Curing compound applied to the panel keyway edges should be removed using a wire brush, wire wheel, or light sandblasting so that the curing compound does not interfere with the bond of the epoxy joint sealant. For accelerated curing processes, careful consideration should be given to the cool-down regimen, particularly when panels are produced under colder ambient conditions. Cracking from thermal shock may occur if the panels are exposed to cold ambient temperatures immediately after heat curing.

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.6 Concrete Placement, Finishing, and Curing

Figure 3.6.3-1 Concrete Curing Techniques

a) Ambient Curing using Curing Compound (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Steam Applied under Plastic Tarpaulins

c) Dry Heat Applied under Curing Cover (being lowered)

d) Supplemental Wet Mat Curing after Stripping

3.6.4 Procedures Following Fabrication Post-fabrication procedures include inspection of the keyways, removal of blockout and dowel slot formers, and trimming and protection of the exposed ends of pretensioning strands. The keyways should be inspected for any anomalies that will prevent keyways from easily fitting together. This includes locations where misaligned joints in the side forms may have left a ridge in the keyway. Any areas that are not flush should be ground so that the keyways fit together properly. Keyways should not be rubbed with grout or mortar to improve appearance or to fill small “bug holes.” This could impede adhesion of the epoxy joint sealant. If larger bug holes are present, they should be filled with grout or mortar and properly cured. The grout or mortar should not protrude from the face of the keyway and the adjacent surfaces ground to a clean condition. Blockout and dowel slot formers should be removed in such a manner to prevent spalling around the edges of the blockouts and slots. If a bond breaking substance, such as form oil, is used on the blockout or dowel slot formers to aid in removal, the vertical faces of the blockouts or dowel slots should be sandblasted to remove all traces of the material. Sacrificial wood blockout formers or steel formers wrapped with a sacrificial layer of polystyrene sheeting have been found to be most effective in minimizing damage to the panels during removal. If significant 3 - 19

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.7 Panel Nonconformance

spalling occurs around a blockout on the top surface of the panel, it may be necessary to saw cut and clean the spalled area for a partial-depth repair, as described in the following section. Pretensioning strands should be trimmed and slightly recessed into the end surfaces of the panels. After trimming, the exposed ends of the strands should be painted or otherwise protected using galvanized paint, epoxy, or an epoxy grout, similar to that typically used for the ends of strands on bridge girders. If the panels are to be installed next to other panels or existing pavement, care should be taken to ensure that the epoxy treatment does not affect the trueness of the end of the panel.

3.7 PANEL NONCONFORMANCE Most nonconformances or minor damage to PPCP panels that occur during production and handling can be repaired at the fabrication plant. Certain imperfections can be accepted without repair if they are deemed to not affect installation or pavement performance. Other defects will need to be evaluated and repaired. Many of the techniques for nonconformance or damage assessment and repair are similar to those for bridge products and are described in the Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products (PCI, 2006). This manual was developed as a resource document to guide owners, designers, inspectors, and fabricators in reaching informed decisions regarding repair options. To this end, the engineering considerations related to individual defects are provided. The ultimate value of the manual depends on the sound engineering judgment of qualified individuals who use it. However, certain defects are more important in pavement panels and are described in the following sections.

3.7.1 Nonconformance and Damage Assessment Defects or damage to precast panels during fabrication and handling (form removal, lifting, transporting within the plant, or in storage) is typically addressed by agency inspectors on a case-by-case basis. Of particular importance for pavement panels is damage to the top surface (riding surface) or to the keyways. Defects and damage to these areas can affect ride quality of the pavement or installation of the panels. Defects and damage to other parts of the panel, such as bottom edges or corners, the bottom surface, blockouts, lifting, or anchor regions, etc., may not affect panel assembly or pavement performance, but still must be assessed. Isolated incidences should be expected, particularly for large projects with numerous pieces. However, if the same defects continue to occur, the fabrication operation should be reviewed immediately and the cause determined and addressed. The following sections describe defects that have been observed during fabrication of PPCP panels. 3.7.1.1 Spalls Spalls occur for many reasons including point loads along the edges of a panel. Some result from stripping form work and others from contact between panels during handling. They may be very shallow or as much as half the panel thickness in depth. Several types that have been observed are described below and illustrated in Figure 3.7.1.1-1. Surface Spalls―Generally, surface spalls less than ¼ in. deep will not require repair, particularly if the pavement surface is to be diamond ground after installation. If the spalled area is particularly large (e.g., greater than 4 in. in diameter), and the surface will not be diamond ground, repair should be considered. Spalls deeper than ¼ in. should be repaired. Keyway Spalls―Keyway spalls that may affect assembly of the panels or grouting of the post-tensioning ducts should be repaired. Spalls less than ¼ in. deep may not require repair, but any loose material should be thoroughly removed. Spalls deeper than ¼ in. should be repaired or the panel rejected if deep spalls are present over more than 25% of the length of the keyway. Spalls of the keyway around the post-tensioning ducts may prevent a tight seal of the ducts between panels, and should be repaired. Panel Edge and Corner Spalls―Spalls of panel edges and corners that abut adjacent pavement or other PPCP panels should be repaired so that a durable joint is accomplished. Spalls of an exterior edge or corner (e.g., in the shoulder) of the panel may not need to be repaired, pending determination of the agency.

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Blockout, Lifting Insert, and Grout Port Spalls―Minor spalls (less than ¼ in deep) around the top edges of blockouts may not require repair. Spalls deeper than ¼ in. should be repaired. For deep repairs, it may be advantageous to simply prepare the spalled area for a partial-depth repair and finish the repair when the blockout is filled in the field. Minor spalls around lifting anchors or grout ports may not require repair. Deep spalls should either be repaired or prepared for patching in the field when the lifting anchors and grout ports are filled.

Figure 3.7.1.1-1 Examples of Fabrication-Related Spalling

a) Surface Spall (crack filled with epoxy)

b) Keyway Spall (bottom lip of keyway)

c) Edge Spall (above pretensioning strand)

d) Blockout Spall (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

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e) Grout Port Spall 3.7.1.2 Cracks Cracks should be assessed after release of prestress because the prestress compression may close some cracks. For jointed precast pavement panels, assessment of cracking should consider the level of reinforcement in the panels, since most of these panels are heavily reinforced, so cracks that do form should be held to a small size. Cracks observed in the panel surface should be assessed to determine if they are shallow surface cracks or deeper. This may require core-drilling through the panel using a 1- to 2-in.-diameter core drill at the location of the crack. Extensive cracking is cause for ceasing fabrication until the cause can be determined and eliminated. The acceptance of cracks in panels must be at the discretion of the owner agency. Several examples of surface cracks are shown in Figure 3.7.1.2-1. Surface Cracks―Surface cracks may include shallow longitudinal or transverse cracks, random, and y-cracks, or plastic shrinkage cracks. Narrow surface cracks, 0.007 in. or less in width may not require any treatment. Cracks wider than 0.007 in. should be repaired by epoxy injection, particularly if the pavement will be exposed to deicing chemicals. If not exposed to deicing chemicals, cracks up to 0.012 in. in width may be allowed without treatment. Full-Depth Cracks―Full-depth cracks should be carefully evaluated to determine the likely cause. Full-depth cracks can have a significant effect on pavement performance. Full-depth cracks that are not closed by prestressing to 0.007 in. or less in width may be cause for rejection of the panel, particularly if the panels will be exposed to deicing chemicals. For panels not exposed to deicing chemicals, crack widths up to 0.012 in. may be permissible. Alternatively, epoxy injection can be used to repair the crack with the understanding that reoccurrence of the crack or additional cracking after repair may be cause for rejection. Multiple full-depth cracks may be cause for immediate rejection. Keyway Cracks―Cracks along keyways may be repaired only if it is determined that the cracks will not affect assembly of the panels. Cracks extending more than 25% of the length of the keyway or those that are believed to weaken the keyway may be cause for rejection of the panel. Cracks up to 0.007 in. wide may not need repair, while cracks wider than 0.007 in. should be repaired using epoxy injection if the panels will be exposed to deicing chemicals. Crack widths up to 0.012 in. may be permissible before sealing is necessary if the panels will not be exposed to deicing chemicals.

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Figure 3.7.1.2-1 Examples of Fabrication-Related Cracks

a) Surface Crack

b) Surface Crack due to Shrinkage

c) Keyway Crack 3.7.1.3 Form Ridges on Keyways Ridges or bulges on the keyways or mating edges will affect assembly of the panels by not permitting the joints to fully close, or preventing a tight joint between the new panels and adjacent pavement. These ridges are generally caused by small gaps in or misalignment of formwork and must be repaired if keyway tolerances are exceeded. Figure 3.7.1.3-1 shows a keyway with this ridge due to the edge forms.

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Figure 3.7.1.3-1 A Ridge in the Keyway Surfaces due to a Form Joint (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

3.7.1.4 Dipping of Panel Edges During concrete placement and finishing, isolated low areas can occur along the edges of panels. Low areas of the tops of mating panel edges should be repaired if the finished edge is out of tolerance for trueness or thickness. Low exterior panel edges (edge of shoulder) may or may not require repair, at the discretion of the owner agency. 3.7.1.5 Corner Breaks The corners of panels are vulnerable to damage from handling as shown in Figure 3.7.1.5-1. Corner breaks should be repaired. Figure 3.7.1.5-1 Cracks Visible Indicating a Broken Corner

3.7.1.6 Keyway Breaks Keyways are also susceptible to damage during removal of the forms and in stripping from the form and handling as shown in Figure 3.7.1.6-1. These breaks should be repaired.

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Figure 3.7.1.6-1 Extensive Keyway Damage

3.7.1.7 Surface Defects Surface defects include indentations, scaling, and texture distortions. Two examples are shown in Figure 3.7.1.71. If the pavement surface will be diamond ground, marred surfaces, including scaling, may be accepted, depending on the depth of the scaling or indentations. If the surface will not be diamond ground, shallow indentations may be accepted at the discretion of the agency, but more severe surface scaling and texture holidays should be repaired or the panel rejected. Figure 3.7.1.7-1 Finished Surface Defects

a) Surface Scaling

b) Aggregates Dislodged during Finishing

3.7.2 Panel Repair Techniques Repair procedures for precast pavement panels are essentially the same as those used for other precast concrete products. Many types of repairs are described in the Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products (PCI, 2006). However, there are some important distinctions for PPCP panels. First, PPCP panels must fit together properly on site. This requires careful attention to the repair of mating edges, keyways in particular, to ensure that repaired areas are within tolerance dimensionally and for trueness. Second, the top surface of PPCP panels is the riding surface of the pavement. This requires careful attention to the effect that repairs, if permitted, have on ride quality and durability. Repair material must have significant strength and be adequately bonded to the adjacent surfaces. Diamond grinding of the pavement surface on site may remove minor surface defects, but cannot correct larger ones. 3 - 25

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For shallow surface cracks, low viscosity sealing materials, such as methyl methacrylate can be used to fill the cracks by gravity flow or by toweling with a squeegee (Fig. 3.7.2-1). For deeper and wider cracks, epoxy injection is commonly used. Epoxy injection uses pressure to force the epoxy deep into the crack to bond the two sides of the crack together and seal it from water intrusion. For shallow spalls or indentations that require repair, epoxybased mortar materials can be used. Partial-depth repair techniques are commonly used to repair deep surface spalls, edge spalls, keyway breaks, or corner breaks. For partial depth repairs, saw cuts are made a minimum of 2 in. deep into the surface, edge, or keyway just beyond the limits of the damaged area (Fig. 3.7.2-1). Saw cuts in the top surface of the panel should not form corners with angles less than 90 degrees in order to reduce the risk of reentrant cracks propagating from these corners. After saw cutting, unsound concrete material should be removed using a lightweight chipping hammer. Formwork identical to that used for the initial fabrication should be used to form the patch. For deep edge spalls, keyway or corner breaks deeper than 2 in., it may be necessary to drill and epoxy No. 3 or No. 4 reinforcing bars into the panel prior to patching to help anchor the patch in place. This reinforcement should be positioned so that proper concrete cover is provided within the patch. Epoxy-based patching materials have been used with good success for partial depth patches. It is important that any repaired areas on the keyways be properly finished and ground as necessary to ensure that the repair does not protrude from the plane surface of the keyways, preventing mating keyways from fitting together. Repairs should not cause the keyway or other surfaces to exceed tolerances. Grinding can also be used to remove any ridges formed along the keyways due to formwork issues. Figure 3.7.2-1 Examples of Panel Repairs in Progress (Photos: David Merritt, Center for Transportation Research, University of Texas at Austin)

a) Spalled Keyway Repair (Spalled Area Saw Cut and Removed)

b) Spalled Blockout Repair (Spalled Area Saw Cut and Removed)

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.8 Lifting and Handling

c) Surface Crack Filled with Epoxy by Gravity

3.8 LIFTING AND HANDLING 3.8.1 Lifting Devices An important consideration for selecting the type of lifting device is that the top surface of the panel will be the driving surface of the finished pavement. Therefore, minimizing the “footprint” of the lifting device should be considered, particularly if the pavement must be opened to traffic prior to patching over the lifting device. The smaller the area to patch, the better the performance will be because many lifting anchor patches will be exposed to heavy traffic, freezing conditions, de-icing salts, and snowplows. Threaded coil lifting insert anchors (Fig. 3.8.1-1) generally leave the smallest recess to fill, have a rough interior surface to anchor the patch, and will permit the pavement to be opened to traffic prior to patching without concern for adverse effects on traffic. Caution must be exercised when using coil lifting inserts, to assure that the proper number of threads are engaged when screwing in the coil bolt. It is common for debris to fill such inserts and make screwing in the bolt difficult. If only a few threads are engaged the embedded coil unwinds and the insert fails. “Quick connect” type anchors have also been used in pavement panels, and provide a lifting anchor that can be released from the lifting lines much quicker than a threaded coil insert (Fig. 3.8.1-1). However, these systems typically leave a larger recess that needs to be patched prior to opening to traffic, especially considering motorcycle wheel hazards. These systems also require special preparation such as sandblasting of the embedded anchor head and recess surfaces to ensure the patch material bonds to the steel and surrounding concrete. Most of the lifting anchor systems commonly used for precast concrete units are available in capacities that can accommodate the weight of PPCP panels using a four-point lifting configuration. Because it is likely that the pavement surface will be diamond ground after installation for most applications, lifting anchors should be recessed at least ½ in. from the panel surface to reduce the possibility of the diamond cutting heads hitting the lifting anchors and exposing the steel. In addition, because the lifting anchors will have only minimal concrete cover, often ½ in. or less, galvanized, epoxy-coated, or stainless steel anchors should be specified to prevent corrosion. Selection of the lifting devices should be a joint decision by the panel supplier and installation contractor with the approval of the owner.

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Figure 3.8.1-1 The Impact to the Surface of various Lifting Devices used in PPCP Panels

a) A Type of “Quick Connect” Anchor Pocket Showing Headed Lifting Stud

b) Another Type of “Quick Connect” Pocket with Lifting Anchor Shown

c) Simple Recessed Threaded Coil Lifting Insert

3.8.2 Recommendations The fabricator should specify a lifting configuration that will minimize stresses in the precast panels during handling, particularly during early age handling when removing the panels from the forms. Variations in panel thickness, overall dimensions, and the location of reinforcement and embedments should all be taken into account to ensure that the load is evenly balanced on the lifting lines. This is particularly important for installing the panels on site so the panel hangs level and can be safely maneuvered. The Design Handbook (PCI, 2010) provides excellent guidance for lifting configurations for precast concrete panels. Typically, a four-point lift will be adequate and safe for the size of precast panels used in PPCP. It is essential that the lifting configuration is thoroughly checked by the precast producer prior to beginning panel fabrication. To minimize bending stresses in the panels and forces in the lines and lift devices during handling, lifting lines should form an angle of no less than 60 degrees where they intersect with the precast panel. A spreader beam may also be used to maximize the angle between the lifting lines and panel surface, as shown in (Figure 3.8.2-1 c and d). For joint panels, a strongback is typically mounted to the top surface of the panels to prevent the expansion joint from opening or flexing during lifting and handling. The lifting anchors cast into the panels can be used to mount the strongback to the panel surface, as shown in Figure 3.8.2-1a and b. 3 - 28

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Figure 3.8.2-1 The use of Strongbacks and Spreader Beams for Handling Panels

a) Strongback Bolted to the top of a Joint Panel

b) Strongback Mounted to the End of a Joint Panel

c) Spreader Beam used with a Wheeled Travel Lift to keep Lift Lines Vertical

d) Spreader Beam used with a Fork Lift for Handling Panels (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

3.8.3 Storage and Shipping Panel storage practices should be similar to those typically used for other precast panel products. Panels can be stacked, provided proper dunnage is provided between them, as shown in Figure 3.8.3-1. Dunnage should be stacked one above the other vertically in such a stack to ensure that excessive stresses are not induced in any panel from misaligned dunnage. Dunnage is typically positioned at the same locations as the lifting anchors, but this configuration should be verified by the producer prior to storage. Panels that are produced as warped (see Sect. 3.10 for warped panels) should be stored and shipped on dunnage positioned in a three-point (tripod) layout. It is critical that the foundation under the stack is strong and level so that the panels will not sink into the ground, warp or twist. The bottom supports should be surveyed to ensure that each support is itself level, and that there is no significant difference in elevation between the two supports. Panel shipping procedures should follow standard practice for other precast panels. Depending on the size of the panels and local trucking weight restrictions, one to three panels are typically shipped on each truck, as shown in Figure 3.8.3-1. The panels should be properly supported on the truck and secured using straps that will not damage the corners or top edges of the panels. If chains are used, adequate blocking or padding should be provided to prevent damage to the edges and keyways of the panels. Placement of dunnage on the truck should be 3 - 29

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similar to that used for storage at the plant. Long panels (e.g., 24 ft or more) should be carefully evaluated to ensure prestress levels are adequate for the support configuration and any potential dynamic flexure during shipment. Shipment of precast panels should be thoroughly evaluated during the design and project layout stage to strike a balance between optimization of panel size for production and shipment. Panels over 8 ft wide may require an oversize load permit, depending on local shipping restrictions. However, the cost of oversize load permits may be more than offset by the increase in production and installation rates using wider panels. Weight restrictions should also be considered, as it may be more cost effective to use a specialty truck with more axles to ship more panels on a load than to ship more loads. Figure 3.8.3-1 Panel Configurations for Storage and Shipping

a) Storage of Panels with Variable Thickness

b) Storage of Panels with Uniform Thickness (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

c) Shipment of a Single Panel of Width Greater than 8 Ft

d) Shipment of Multiple Panels (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

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3.9 ACCEPTANCE TESTING AT FABRICATION PLANT Some basic acceptance tests at the precast plant will help to ensure installation goes smoothly, and can help identify possible fabrication issues early in the process. These tests include a panel fit-up check and posttensioning duct check.

3.9.1 Panel Fit-Up Using nonmatch-cast panels for PPCP requires careful attention to the formwork to ensure that the keyed panel joints fit together properly. Prior to beginning large-scale production of panels, a panel fit-up test should be conducted with the first few panels that are produced, as shown in Figure 3.9.1-1. This test can be used to identify issues with the keyway forms. It is recommended that PPCP specifications require at least three panels be fabricated and test fit at the fabrication plant for this purpose. Ideally, the panels should be assembled over a graded base with polyethylene sheeting used to simulate actual field conditions. However, if it is not feasible to grade a section of base to the proper tolerances, the panels can be assembled over a flat concrete slab or on the rails of a casting bed. It is not necessary to apply epoxy to the panel joints in this test so they may be used in the project, but a post-tensioning strand should be fed through each duct of the assembly to identify issues with alignment of the ducts between panels. If the panels do not fit together properly, as indicated by joints not closing completely or by nonuniform contact along the top of the joint, the accuracy of the side forms should be improved. Likewise, if the ducts do not align between panels, the positioning of the ducts (or holes drilled in the side forms to locate the ducts) should be checked and adjusted. In addition to the initial panel fit-up check, subsequent tests should be conducted whenever there is any change in forms, panel sizes or processes. As a general guideline, a panel fit-up check should be conducted after every 8 to 10 casts, or after every 50 panels produced. If the contractor is experiencing any problems with fitting the panels together on site, and it is determined not to be an installation problem, production should be halted and a panel fit-up test conducted immediately to determine if there is an issue with fabrication.

Figure 3.9.1-1 PPCP Panel Fit-up Tests at the Fabrication Plant prior to Full-Scale Production (Left Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

3.9.2 Duct Inspection A very important investigation at the fabrication plant is for blockage in the post-tensioning ducts. Blockage may be caused by ducts being crushed during fabrication, dowel stiffeners inadvertently left in the ducts, formation of ice, or rodent nests (if panels are stored for long periods of time), to name a few. This duct check is usually accomplished by simply feeding a post-tensioning strand or bar of the same size that will be used for final longitudinal post-tensioning, through each duct to check for obstructions. This check should be performed immediately after the panels are moved to storage in case there is an issue (e.g., crushed duct) that can be immediately corrected. If 3 - 31

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the panels will be stored for a long period of time, the ducts should be capped after the duct check is complete to identify that they have been checked and to protect them in storage. The caps should be removed just prior to installation of the panels at the project site. The ducts should also be checked for residual water as a result of steam curing. This is particularly important if the panels are to be stored in sub-freezing temperatures as the water may freeze and create a blockage. Water should be blown out using compressed air and the duct capped to prevent additional water from rain or snow from entering the duct during storage.

3.10 FABRICATION OF JOINTED PRECAST PAVEMENT PANELS Fabrication of panels for jointed precast pavement systems (JPPS) presents a unique set of considerations for fabrication. Many of the guidelines presented in the previous sections for PPCP panels apply to fabrication of jointed precast pavement panels. However, some important distinctions will be addressed in this section. These differences are associated with the way jointed panels are installed and used.

3.10.1 Uniqueness of JPPS JPPS panels often have a wider range of dimensions and sizes than PPCP panels because they are used in a wide range of applications such as horizontal curves, superelevation transitions, intersections, and ramp termini, and for replacement for portions of existing concrete pavement between existing longitudinal joints. Variable panel geometry requires special consideration of the quality assurance process, tolerances, forming and verifying that each unit conforms to required dimensions.

3.10.2 Quality Assurance Most JPPS panels are not prestressed so the quality assurance requirements for prestressing do not apply. Load transfer mechanisms between panels are typical load transfer dowels. The plant Quality Systems Manual must include details for assuring quality in the installation and inspection of these devices. Jointed precast concrete panels must be fabricated in plants that are PCI-certified as discussed in Section 3.1. 3.10.2.1 Pre- and Post-pour Inspection In addition to variable plan dimensions, jointed panels are frequently used to replace three-dimensional pavement surfaces. The plant Quality Systems Manual must specifically address methods for checking the panels in all three dimensions before and after the concrete is cast. The consequences of an incorrectly fabricated panel being delivered to the job site during a limited work window are very significant, so the importance of this procedure cannot be over emphasized. 3.10.2.2 Tolerances Typical dimensional tolerances for jointed precast panels are similar to those listed for PPCP panels but also include tolerances for dowel bar and slot positioning, as shown in Table 3.10.2.2-1. Table 3.10.2.2-1 Tolerances for Jointed Precast Pavement Panels Width and Length Length of Computed Diagonal Shown on Shop Drawings Thickness Surface Tolerance Measured from a Theoretical Plane Established by Corner Elevations Edge Squareness Measured in Relation to Top and Bottom Edges Dowel Variance from Level, Squareness to Edge of Slab, and Horizontal and Vertical Location Slot Horizontal Location and Squareness to Edge of Slab Lifting Anchor Location

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±3/16 in. ±1/4 in. ±1/8 in. ±1/8 in. ±1/16 in. ±1/8 in. ±1/8 in. ±6 in.

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The tolerances shown in Table 3.10.2.2-1 are necessary to ensure that maximum pavement joint widths permitted by the specifying agency are achieved. The tolerances also help to ensure that installed multiple panels do not grow short or long. Most agencies specify a maximum pavement joint width of 3/8 to 1/2 in., which necessitates an allowable panel length and width tolerance of between ±3/16 and ±1/4 in. The plant Quality System Manual should clearly indicate when and how measurements are to be taken to determine conformance to the stated tolerances. Surface tolerance for a warped panel, for example, is most effectively through checking the form before casting. It is very difficult to check the top surface of the panel for surface tolerance after it has been finished with a texture. The accuracy of the bottom surface of a panel is especially important in slab-on-grade systems where the subgrade surface provides grade control. The best way to ensure an accurate bottom panel surface is to make sure the form surface is constructed to the tolerance listed in Table 3.10.2.2-1, and will be discussed in Section 3.10.3. Panel thickness is difficult to measure except along the edges of the panel. However, it should be checked and necessary changes made to side rail heights.

3.10.3 Formwork The general comments made in Section 3.2.4, Formwork, apply to casting beds for all precast panel systems, including jointed precast concrete panels. Forms for jointed panels should conform to the rule of thumb for form accuracy cited in that section of “one-half the allowable dimensional tolerance for the product.” A form surface accuracy of ±1/16” from the plane defined by the four corners of the panel is a very exacting tolerance and can only be achieved by using heavy duty, rigid steel form beds that maintain dimensional accuracy over multiple casts. Side rails for jointed panels should be built with the necessary variability of jointed panel dimensions in mind. An exaggerated plan view of a jointed panel is shown in Figure 3.10.3-1. The side rails must be designed to easily accommodate side dimensions that change from panel to panel even though these changes may typically be very small. Figure 3.10.3-1 Exaggerated Plan View of a Jointed Precast Pavement Panel (Drawing: The Fort Miller Co., Inc.)

Embedded dowels and tie bars are located as required by the specifying agency and as necessary to align with corresponding cast-in slots. Most states require a dowel spacing of 12 in. on center over the length of the entire transverse edge of the panel, or alternatively, three or four dowels in each wheel path, spaced at 12 in. on center, depending upon the type of repair project. In either case, the side rails must be designed to accommodate whatever spacing is specified, keeping in mind the lengths of transverse sides are rarely an even number of feet as shown in Figure 3.10.3-1. As a result, end spaces D and B may not be equal and may vary from panel to panel. The precaster must work with the panel designer to minimize these changes and keep the casting process as simple and efficient as possible. 3 - 33

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Three-dimensional pavement surfaces that constitute a warped rather than a flat plane require warped precast panels with a surface cast to the identical geometry of the pavement surface it is furnishing. An isometric view of a warped panel is shown in Figure 3.10.3-2.

Figure 3.10.3-2 Isometric View of a Warped Precast Panel (Drawing: The Fort Miller Co., Inc.)

Sections taken through B-D and A-C are shown in Figure 3.10.3-3. The amount of warp is quantitatively shown as “∆.”It is defined as the vertical distance between elevation D and a plane drawn through the other three corners (corners A, B, and C).

Figure 3.10.3-3 Cross-sectional Views of Warped Precast Panels (Drawing: The Fort Miller Company, Inc.)

The panel shown in Figure 3.10.3-2 can be fabricated on a flat casting bed using variable-height side rails. This would result in a panel with a flat bottom surface and a warped top surface as shown. The resulting variablethickness panel must be placed on a subgrade surface that is graded flat. While this may work for a single panel, it is problematic for a series of adjoining panels because a unique and different subgrade surface would need to be created for each adjacent panel. A more constructible approach is to cast a constant-thickness warped panel on a bed that is warped to a plane that is parallel to the plane of the top surface. The resulting constant thickness panel may then be placed on a subgrade surface that has been graded parallel to the required pavement surface in the traditional manner that cast-in-place concrete pavement is built. A proprietary forming system is available to cast constant-thickness warped panels. It utilizes a form that can be adjusted to an upward warp of a maximum of approximately 4 in., as shown in Figure 3.10.3-4. The form is positioned in the precast plant such that corners A, B and C are level. Corner D is adjusted to the specific warp 3 - 34

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.10 Fabrication of Jointed Precast Pavement Panels

dimension “∆” for each panel. The form is also designed to cast a warped non-rectangular panel such as that shown in Figure 3.10.3-1. Figure 3.10.3-4 Proprietary Casting Table and Forming System for Warped Precast Panels (Photo: The Fort Miller Company, Inc.)

3.10.4 Materials The information provided in Section 3.3, Materials, applies to jointed precast pavement panels. Although jointed panels may be prestressed, they are most frequently reinforced with conventional reinforcement. Therefore, references to pretensioning and post-tensioning materials may not apply. 3.10.4.1 Concrete If jointed pavement panels are not prestressed, their minimum required concrete compressive strength at stripping will usually be between 2,500 and 3,500 psi, depending upon their weight and the type of lifting anchor used. The minimum stripping strength should be determined on a job-by-job basis taking these factors into consideration. 3.10.4.2 Tie Bars and Threaded Dowel Bar Splice Couplers Tie bars are used in conventional cast-in-place and jointed precast concrete pavement to tie adjacent lanes together across longitudinal joints. The typical embedment length in each lane or panel is 15 to 18 in., depending upon specific agency requirements. Two-piece tie bars are frequently used in precast jointed panels to minimize panel widths for shipping purposes and allow easier forming. The threaded “receiving” half is cast in the panel leaving a clean panel edge. The remaining half of the dowel is shipped loose and screwed into the receiver in the precast panel in the field. Tie bars and couplers must be fabricated from deformed and corrosion-protected reinforcing steel bars meeting agency-specified AASHTO/ASTM standards. 3.10.4.3 Dowels Most jointed precast pavement systems utilize standard smooth steel dowels across transverse joints for load transfer. Epoxy-coated steel dowels are most commonly used in jointed panels but other corrosion-resistant dowels such as zinc coated, stainless steel, stainless steel clad, and fiberglass dowels may be allowed by the specifying agency. If dowels are cast in the panels, care must be taken to position them to accurately align with slots cast or cut in the adjacent panel. Epoxy-coated dowels should be handled with care because the coating is easily compromised if they are dropped or scraped. If the dowels penetrate the side rails during the casting process, the rails should be stripped away 3 - 35

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.11 Resources for Additional Information

carefully to avoid damaging the epoxy coating. In addition, dowels in finished panels should be protected during storage and shipping to prevent damage to the epoxy coating. If the coating is damaged, it should be repaired by using an agency-approved method prior to final installation. 3.10.4.4 Dowel Bond Breaker Before concrete is placed in the form, dowels should be coated with an agency-approved bond breaker, preferably a white lithium or similar grease. Bond breaker material should be applied in strict accordance with the manufacturer’s instructions. Polymer expansion caps should also be placed on the cast-in end of the dowel in accordance with agency specifications. 3.10.4.5 Lifting Devices Lifting inserts should be galvanized or otherwise corrosion-protected as required by the specifying agency. Most importantly, they should be sized in strict accordance with the manufacturer’s design directive as they are an important safety issue.

3.10.5 Concrete Placement, Finishing, and Curing The information presented in Section 3.6, Concrete Placement, Finishing, and Curing, also applies to jointed precast concrete pavement panels.

3.10.6 Finishing Procedures after Fabrication All panels including jointed, should be examined carefully, prior to yard storage to ensure defects are identified and repaired in an approved manner. All form ridges or other irregularities must be removed. Particular attention should be paid to the top edges to make sure they are rounded slightly to prevent spalling while the panels are in service. It is very important that dowel slots, whether they are cast on the bottoms or the tops of the panels, be cleaned of all forming debris. Vertical slot surfaces should be sand blasted in accordance with agency specifications for dowel bar retrofit procedures to ensure good bond between the panel and the grout fill material. One of the most important parts of the finishing procedure is to place a legible and durable label on at least one edge of each panel. The label should be marked with the panel mark number, cast date, project identification number and manufacturer, at a minimum. Some agencies may require additional information.

3.10.7 Storage and Shipping Information presented in Section 3.8.3, Storage and Shipping, also applies to jointed panels but with one exception. Warped panels must be stored and shipped with supports at only three points. The lengths of jointed precast panels are rarely a concern for shipping because they seldom exceed 16 ft.

3.11 RESOURCES FOR ADDITIONAL INFORMATION An online compilation of resources for additional information on precast concrete pavement has been assembled by PCI, and is available at the internet address below. This site will be continually updated as new information becomes available from current and future projects. www.precastconcretepavement.org

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MANUFACTURING PRECAST CONCRETE PAVEMENT PANELS 3.12 Cited References

3.12 CITED REFERENCES AASHTO. 2012. AASHTO LRFD Bridge Design Specifications, 6th Edition. American Association of State Highway and Transportation Officials, Washington, DC. 1,672 pp. https://bookstore.transportation.org/collection_detail.aspx?ID=112 PCI Manual 116. 1999. Manual for Quality Control for Plants and Production of Structural Precast Concrete Products. Fourth Edition. (MNL-116-99). Precast/Prestressed Concrete Institute, Chicago, IL. 340 pp. PCI. 2006. Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products, (MNL-137). Precast/Prestressed Concrete Institute, Chicago, IL. 72 pp. PCI. 2010. Design Handbook, 7th Edition, (MNL-120-10). Precast/Prestressed Concrete Institute, Chicago, IL. 828 pp. https://netforum.pci.org/eweb/DynamicPage.aspx?Site=PCI_NF&WebKey=9766331d-1b7d-4c4b-89cbfc801bc30745&ListSearchFor=design%20handbook (Fee) Salas, R. M., A. L. Kotys, J. S. West, J. E. Breen, and M. E. Kreger. 2002. Final Evaluation of Corrosion Protection for Bonded internal Tendons in Precast Segmental Construction. Research Report No. 0-1405. Center for Transportation Research, University of Texas at Austin. Austin, TX.

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.0 Introduction/4.1 Installation Staging and Sequencing

4.0 INTRODUCTION This is the fourth in a series of four documents on the use of precast concrete pavement systems (PCPS). It provides guidance for construction including topics on scheduling windows, foundation issues, construction procedures, materials, and equipment, panel installation, and post-tensioning. This information has been acquired and reinforced from projects constructed to date. It will assist owner agencies in developing project plans and specifications (including inspection and field guidance), and assist contractors in understanding best practices for the construction process. In defining terminology, when PCPS are prestressed, either pretensioned in the fabrication plant, or posttensioned during construction, they are referred to as precast, prestressed concrete pavement or PPCP. Jointed precast pavement systems (JPPS) are generally not prestressed although they may be. Many of the topics in this document on construction refer specifically to PPCP. Other subjects can be applied to both systems. Generally, the topics and their applications are identified as they are discussed in the text.

4.1 INSTALLATION STAGING AND SEQUENCING Planning the panel installation process is critical for the success of PPCP construction. There are a number of steps, some of which must be completed prior to opening the pavement to traffic.

4.1.1 Type of Project The exact nature of the project (e.g., reconstruction, rehabilitation, new construction, nighttime closures, etc.) will affect staging and sequencing through:   

the plan for maintenance of traffic, restrictions on access to the project site, and special requirements for the types of precast panels required.

The maintenance of traffic and related restrictions on access to the project site will affect how the panels are delivered and where construction equipment may be placed. For new construction, there are often relatively few restrictions on site access, and staging is less of a concern. For reconstruction or rehabilitation projects, construction is often adjacent to active traffic, and only one or two lanes may be available for construction and mobilization. New construction may also allow storage of the precast panels on or very near the project site, whereas reconstruction projects may require “just-in-time” delivery of the panels as they are needed for installation. Just-in-time delivery is more risky due to the potential for the delay of delivery trucks, but will generally be more efficient than storing the panels on or near the site because they must be handled more than once. The positioning of equipment will also depend on the type of project. For new construction, it is not necessary to remove old pavement and base preparation can usually be completed well in advance of installation. For new pavement, there may be access to haul roads to minimize construction traffic on the new pavement. For reconstruction, however, removal of existing pavement and the base preparation are often accomplished just prior to panel installation, limiting access for the installation. Reconstruction will probably require the crane and delivery trucks to locate on the new panels as they are installed. While this eliminates issues with damaging the base in front of the installation operation, the weight of the crane can possibly damage a newly installed panel if it doesn’t have full support by the base or is otherwise protected. In terms of sequencing operations for new construction, constraints are primarily the timing of each step in the process, such as scheduling post-tensioning, grouting, etc. For reconstruction, however, the contractor must have confidence in estimates of how long each step takes in the installation process, so that each construction shift can be accurately planned to optimize the amount of pavement that can be installed and made ready for traffic. Fortunately, many of the steps in PPCP construction can be completed in separate construction windows, allowing panel installation to proceed independently from other processes such as final post-tensioning, tendon grouting, under-slab grouting, etc. For projects using unique panels, such as match-cast or panels fabricated to fit in a specific location on site, planning for panel installation is much more important since panels are not always interchangeable. Panels must be properly marked at the fabrication plant, delivered to the site and installed exactly in the order, location, and 4-1

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orientation specified. For these projects, contingency plans should be developed in some detail to account for unexpected problems, such as delays in the delivery of panels.

4.1.2 Construction Windows The amount of time allowed for PPCP construction is another factor that will dictate options for staging and sequencing. In terms of staging, the construction window may dictate whether panels are stored near the site or delivered during installation. It may also dictate the type of equipment used for installation and the positioning of the equipment on site. For example, highly mobile cranes may be desirable for the shorter, 8- to 10-hour-long windows. Nighttime construction will require lighting and may result in additional constraints concerning lane closures. In terms of sequencing, the construction window will dictate which and how many steps in the process can be completed and that will determine the productivity possible during each shift. For reconstruction projects with short (8- to 10-hour) construction windows, it may not be possible to complete all steps necessary for a PPCP slab installation in a single shift. Many of the processes will need to be completed concurrently during subsequent construction windows. Within a given construction shift, many concurrent processes may be necessary at different locations such as:         

Saw-cutting of the existing pavement Removal of the existing pavement Base preparation Precast panel installation Temporary post-tensioning Final post-tensioning Filling stressing pockets Tendon grouting Under-slab grouting

The critical steps that must be completed prior to opening the pavement to traffic after panel installation include:   

Temporary post-tensioning Filling or the temporary covering of stressing pockets Providing a transition from the end of the installed pavement to the existing pavement

Also, depending upon the condition of the base, under-slab grouting may need to be performed prior to opening to traffic. Enough time must be permitted to complete these steps within the allowable construction window.      

Later, during subsequent shifts, these final steps may be accomplished: Final post-tensioning Filling the stressing pockets Under-slab grouting Tendon grouting Diamond grinding of the finished surface

Above all, the pavement must be opened to traffic without compromising safety of the traveling public. Preparation and planning for contingencies are essential to ensure that construction can be completed within the allowable construction window.

4.2 BASE PREPARATION Base preparation is a fundamentally important component of PPCP construction. Precast panels do not conform to the surface of the underlying base like cast-in-place concrete pavement. Therefore, the base must be graded accurately, to within a tolerance that will, as much as possible, fully support the panels. If this cannot be accomplished with confidence, an additional bedding procedure, under-slab grouting, must be used to ensure uniform support. One advantage of PPCP panels is the ability to accommodate less than perfect support by having prestress in the pavement. When conditions dictate, additional prestress can be provided to span over voids. 4-2

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Additional prestress should not be used to compensate for an existing base that is in poor condition. For this condition, new base material should be placed, graded, and compacted to the required tolerance. Base preparation will be governed by the project type, location, and the permissible construction window. For new construction, there will likely not be as many constraints on construction time. Conventional concrete pavement base materials and construction processes can be used. For reconstruction projects, however, minimal disruption of the underlying base is the goal and the materials used will need to permit rapid base preparation for those projects with short construction windows.

4.2.1 Equipment Requirements The equipment for base preparation starts with removal of the existing pavement (for reconstruction projects) and extends to construction of the new base. Most reconstruction projects will be completed during short construction windows, so minimizing disturbance or damage to the base will reduce preparation time prior to installing new panels (unless, of course, replacement of the base is required). For this reason, non-impact methods of pavement removal, such as saw cutting and lift-out methods commonly used for cast-in-place concrete pavement are desirable and should be used whenever practical. If an existing asphalt concrete pavement is being reconstructed with PPCP, it may be possible to mill the asphalt pavement to the depth required and use it as a base for installing new panels. Base preparation should be carefully planned so that it will not impede installation of the PPCP panels. Equipment for removing existing pavement and base preparation must be capable of advancing ahead of panel installation. Equipment used for base preparation must “fit” into the space where the panels will be installed. This may be limited to as little as one lane (12 ft) wide and less than 100 ft long. It will generally eliminate the use of asphalt paving machines (and therefore the use of asphalt bases for the new pavement) or slipform pavers (for cementitious bases such as lean concrete). Hand operated grading devices or other portable equipment, such as concrete floor finishers, will likely be required for projects with space constraints. For new construction, a new base is typically constructed over the entire length of the project before panel installation begins. This permits the use of more conventional equipment and materials. Regardless of the type of construction (new or reconstruction), consideration should be given to the capability of the base to withstand loads from construction traffic (including the workmen’s foot traffic) prior to and during panel installation. Equipment staged on the base during panel installation such as crane and delivery trucks should not damage the base prior to panel installation, because any damage must be repaired.

4.2.2 Types of Bases There is no specific base required for PPCP. For new construction, base materials normally used beneath concrete pavements where the project is located should be utilized since the performance of these materials is known. For reconstruction projects, the existing base should be left intact whenever practical, unless there is evidence that it is not suitable for supporting new pavement (e.g., drainage issues or significant swelling/shrinkage, etc.). If reconstruction of the base is necessary, typical base materials should be used, but consideration must be given to the constructability of the base inside the available construction window. On projects completed to date, several methods and materials have been used (see Fig. 4.2.2-1). These bases include: dense graded hot mix asphalt concrete, permeable asphalt treated base, lean concrete, pervious portland cement concrete, and crushed aggregate. In reconstruction projects where only a nominal level-up base is needed, usually less than 1-in. thick, fine graded aggregate materials have been used successfully, but must be properly compacted prior to the installation of panels. It has been observed that PPCP panels tend to settle into flexible bases under their own weight within 24 hours. These flexible bases include hot mix asphalt and asphalt treated bases. This helps to reduce or eliminate voids beneath the finished pavement, decreasing the amount of under-slab grouting required. However, such settlement may be unacceptable, particularly if it is not uniform, or if the PPCP is placed adjacent to existing traffic lanes. Rigid bases, such as lean concrete, pervious concrete, and large-aggregate stone bases, tend to support the panels at high points on the base surface, leaving voids beneath the pavement that must be filled using under-slab grouting. Slightly retarding the set of pervious concrete has been observed to permit the panels to seat into the base immediately as they are placed. 4-3

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For reconstruction applications, space limitations and construction time constraints generally require a base that can be quickly placed by hand or with portable equipment. The base must be capable of supporting the weight of the precast panels within a short time after it is placed. This may require rapid setting mixtures for lean concrete, or finer graded material for aggregate bases. Hot-mix asphalt materials will generally not be suitable for these applications due to the specialty paving equipment needed to place them and the amount of time required for the asphalt to cool before panels may be installed. PPCP panels will generally be thinner than the pavement that is being replaced. If the new PPCP is only slightly thinner (e.g., less than 1 in. thinner) than the existing pavement, a “level up” base material such as fine graded aggregate, grout, or flowable fill will be needed. In this case it is also desirable to over-excavate the existing base slightly, because it is easier to build up the base than to remove it after panel installation has begun. If the new PPCP is significantly thinner (e.g., 4 to 6 in. thinner) than the combined thickness of the existing pavement and base that has been removed, then a more conventional base must be used. Figure 4.2.2-1 Base Materials that have been used for PPCP

a) Dense Graded Asphalt Concrete (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Permeable Asphalt Treated Base

c) Lean Portland Cement Concrete

d) Crushed Stone

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e) Pervious Portland Cement Concrete

f) Fine Graded Aggregate

4.2.3 Tolerance of Base Surface The surface of the base layer immediately below the PPCP should be graded as smooth and in conformance to the required finished grade as possible prior to installing panels. For new construction, there is more allowance in the time permitted for constructing the base, and correcting it if necessary to achieve elevation and smoothness. For reconstruction applications, the existing base typically remains in place and a level-up base is placed on top to bring it to the proper finished grade. However, a new base may also be constructed if the difference in thickness between the existing pavement and new PPCP is greater than 1 in. The finished grade elevations can be checked using a reference plane established by laser-based surveying equipment or straightedges with digital inclinometers. For base surface smoothness, the following tolerance is typically specified: “The variation of the surface shall be such that a 6-in.-diameter circular plate, 1/8-in. thick cannot be passed beneath a 10-ft-long straightedge in both the transverse and longitudinal directions.” This tolerance should be achievable with most base materials, but may be more difficult with coarse graded crushed aggregate material. A thin layer of fine graded aggregate, grout, or flowable fill may be used to achieve the required tolerance. While this tolerance has proven satisfactory on projects completed to date, an alternative tolerance may be established based on standard practice for pavement base construction in the area of the project. An alternative tolerance should be evaluated during a trial installation prior to implementation.

4.2.4 Grouting Voids under Panels It is desirable for the underlying base to fully support the PPCP panels immediately when they are installed. However, experience has shown that a method to fill voids between the precast panels and the base is normally required. Although some voids are visible along the leading edge or outside edges of the panels after installation, this does not provide an adequate assessment of the extent of the voids. The best practice is to utilize a positive method for filling under-slab voids after panel installation. If a more thorough assessment is still desired, techniques such as deflection testing using a falling weight deflectometer or ground penetrating radar can provide a better indication of the presence of voids. Ports or small ducts are typically cast into and through the PPCP panels at 3 or 4 ft centers in both directions to allow any voids under panels to be easily filled. Ports also can be drilled through the panels on site, depending on the techniques and materials used and how extensive the voids are expected to be. Under-slab grouting (Fig. 4.4.7-1) is the most common technique for filling voids. It has been used for pavement undersealing over the past several decades, and the material and equipment is readily available. However, alternative materials such as urethane have also been used successfully for undersealing and for lifting pavement slabs and bridge approach slabs. Precast pavement systems that rely on urethane injection to lift the slabs to their 4-5

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design elevation have also been developed. This technique should be evaluated on a trial basis before being deployed on a large scale on a project.

4.2.5 Friction-Reducing Membrane A friction-reducing layer or membrane is required between the base and the panel. This layer serves primarily to reduce the friction between the PPCP slab and base. Frictional stresses occur when the panels slide during posttensioning and from daily and seasonal temperature cycles. However, this layer also helps prevent the PPCP slab from bonding to the base. PPCP panels are not designed as a composite system, so preventing bond is important. A single polyethylene sheet (Fig. 4.2.5-1) is commonly used for this purpose because it is economical, easy to install, and has been shown to be effective over the life of the pavement. Other materials such as geotextile fabrics have also been used with success and provide the added benefit of porosity to ensure that water does not become trapped beneath the PPCP slab. Figure 4.2.5-1 Friction-reducing Membranes between the Base and the Panel

a) Polyethylene Sheet

b) Geotextile Fabric

4.3 CONSTRUCTION MATERIALS The following sections summarize the key materials that must be specified and selected prior to construction. This is not an exhaustive list, and actual materials required will depend on the project.

4.3.1 Post-Tensioning Tendons The type of post-tensioning tendon should be clearly specified in the project plans and specifications. Seven-wire, 270 ksi, low-relaxation strands are typically used for most of the longitudinal post-tensioning tendons. Strands are generally 0.6 in. in diameter, but ½-in.-diameter strands can be used as well. Epoxy-coated strands have been used successfully and provide an additional layer of corrosion protection. This is a consideration particularly at the joints between precast panels where the ducts are not continuous unless segment duct couplers have been used. Grit-impregnated epoxy-coated strands provide additional benefits for bond between the strands and tendon grout. Both fine-grit and coarse-grit epoxy-coated strands are currently available. Epoxy-coated strands should be produced in accordance with the Standard Specification for Filled Epoxy-Coated Seven-Wire Prestressing Steel Strand, (ASTM A882) using a process that fully coats the strand wires and fills the interstices between the center wire and the six outer wires. Several types of prestressing strands are shown in Figure 4.3.1-1. Some projects have successfully used high-strength threaded bar tendons to replace at least two of the longitudinal strand tendons. The bar tendons provide a method for temporarily post-tensioning sections of panels together sequentially, compressing the epoxy-coated joints and allowing small groups of panels to be opened to traffic prior to installation of a full section of panels. The threaded bars are inserted into each panel just prior to installation and coupled to the bars extending from the previous panel that are already in place. Threaded bars 4-6

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are generally 1-in.- to 1½-in.-diameter, 150 ksi, and may also be epoxy-coated for corrosion protection. If the bars are epoxy coated, couplers should be epoxy-coated as well, and care should be taken to protect the epoxy coating during construction. The couplers should contain internal stops that will ensure that each bar is threaded fully into the coupler. Transverse post-tensioning tendons may be strand or bar tendons, but strand tendons are more commonly used. Similar to longitudinal tendons, seven-wire, 270 ksi, low-relaxation strands are typically used. These may be either 0.6-in.- or ½-in.-diameter strands, but the ½-in. strands are more flexible and better able to accommodate crowned cross sections. Epoxy-coated strands may be used if the project is to be constructed in an aggressive environment. Figure 4.3.1-1 Coated and Uncoated Prestressing Strands

a) Seven-wire Prestressing Strands from the Top: Uncoated; Smooth Epoxy-Coated; Fine GritImpregnated Epoxy-Coated; Coarse Grit-Impregnated Epoxy-Coated

b) Close-up of Cross Section of Epoxy-Coated and Epoxy-filled Strand

4.3.2 Joint Epoxy Epoxy applied to the joints between precast panels serves primarily to seal the joints against water intrusion and bond the panels together so that they act as a continuous slab after post-tensioning. In addition, the epoxy acts as a lubricant to seat the keyways during installation of the panels. A high-viscosity epoxy with paste-like consistency, which can be applied a minimum of ⅛ in. thick, is recommended. The epoxy is applied to both panel surfaces of the joint. The application is shown in Figure 4.3.2-1. This type of epoxy will help to fill gaps or unevenness between the mating faces of the panels, ensuring a sealed joint. The epoxy should be suitable for bonding hardened concrete to hardened concrete. Epoxies specifically formulated for segmental bridge construction will meet the requirements for PPCP. The open time or working life of the epoxy should be long enough after mixing so it will remain plastic and flowable while the panels are installed through temporary post-tensioning. This will determine how long in advance of installation the epoxy can be applied to the panel joints. Slow-setting epoxies with open times of up to 8 hours are currently available and have been used successfully on projects to date.

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Figure 4.3.2-1 Epoxy Application to Keyways during Panel Installation

a) Application of Joint Epoxy with Cloth (Photo: Merritt et al., 2002)

b) Epoxy Applied to both Faces; Post-tensioning Strands are seen between Panels Prior to Moving Them Together. Note Epoxy kept away from Ducts.

4.3.3 Tendon and Under-slab Grouts Post-tensioning tendon grout should be a low-shrinkage, low-bleed, high-strength grout that exhibits thixotropic properties. It should be a prepackaged grout conforming to the requirements for Class C grout specified by the Post-Tensioning Institute’s Specification for Grouting of Post-Tensioned Structures (PTI M55.1). Under-slab grouts should not deviate significantly from those used by agencies for under sealing conventional PCC pavements. Under-slab grouting should use minimal line pressure to distribute the grout and avoid unintentional lifting of the panels. A low-shrinkage, highly flowable grout should be used. High-strength, lowbleed grout is not required, but the grout should be formulated so it will reach an initial set prior to opening the pavement to traffic. Grouts may be formulated with any or all of these components as having been shown to perform as required: Type I, II, or III portland cement, fly ash, and fluidifiers (for flowability). Chlorides should not be used to accelerate set times. Urethane injection has also been used in place of grout for filling voids beneath precast pavement slabs.

4.3.4 Expansion Joint Seals The type of expansion joint seal should be specified in the project plans. Seals are typically pre-formed elastomeric strip seals or closed-cell seals, but may also be a poured-in-place silicone seal on backer rod for expansion joints which are not anticipated to open and close more than ½ in. Three types of seals are shown in Figure 4.3.4-1. Detailed information concerning the properties and performance characteristics of joint sealing materials should be obtained from the manufacturers for specific applications. The seal must be sized to accommodate the maximum expansion (stretch) and compression movement specified in the project plans and specifications. The initial joint width, prior to installing the seal, should be considered in determining the seal movement requirements, as well as the minimum joint width the seal can accommodate and the minimum required width for installation.

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Figure 4.3.4-1 Expansion Joint Seals

a) Preformed Elastomeric Seal (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Preformed Closed Cell Seal

c) Poured Silicone Seal with Header Material

Other expansion joint designs can be considered based on constructability, proven performance, and cost.

4.3.5 Materials to Fill Holes and Pockets Material used to fill lifting anchor recesses will depend on the type of lifting anchor and the requirements for opening the pavement to traffic. In general, cementitious mortars or grout materials are suitable for filling these recesses, but epoxy grouts may provide a more durable patch for larger recesses. Lifting anchors that have smaller recesses like threaded coil rod anchors, can be left unfilled initially under traffic and later patched with grout. Larger recesses that must be filled prior to opening the pavement to traffic will likely require a rapid strength-gain patch material. Careful attention should be given to the selection of the material and preparation of these larger recesses because there is concern that the material will work out under traffic. The use of an epoxy bonding agent applied to the inside surface of the recess is recommended to help adhere the fill material to the precast panel. For post-tensioning pockets, the fill material will primarily be governed by the requirements for opening the pavement to traffic. Ideally, conventional portland cement concrete, similar to that used to cast the precast panels should be used (see Fig. 4.3.5-1). However, if the pavement must be opened to traffic soon after placement of the fill material, rapid setting concrete mixtures will be required. Rapid setting mixtures should use only non-chloride accelerators as there may be contact with post-tensioning tendons or anchorage hardware. They should also be specified as non-shrink materials with good freeze-thaw resistance (in colder climates), and should attain strength quickly enough to meet traffic requirements. Concrete mixtures with a nominal maximum aggregate size of ⅜ in. to ¾ in., depending on the size of the pocket and availability of material, should be used in lieu of grouts or mortars which will likely exhibit large shrinkage.

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Figure 4.3.5-1 Pea Gravel Concrete Mixture (left) and Rapid Setting Concrete Mixture (right) Shown being used to Fill Stressing Pockets.

a) Pea Gravel Concrete Mixture

b) Rapid Setting Concrete Mixture

Some agencies permit the use of temporary fill material or steel plates to cover the pockets temporarily until they can be permanently filled during a subsequent closure. Cold-patch asphalt materials, shown in Figure 4.3.5-2, have been successfully used to temporarily fill these pockets. It is important to note, however, that the pockets should either be lined with plastic sheeting or thoroughly cleaned after the cold-patch material is removed to ensure the final fill concrete bonds to the pocket. Steel plates with cold-patch asphalt wedges have also been used as temporary covers. This technique may not be suitable for high-speed roadways, however, as it can create a safety hazard for vehicles. Figure 4.3.5-2 Cold Patch Asphalt Shown used to temporarily Fill Stressing Pockets for Rapid Opening to Traffic

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4.4 PANEL INSTALLATION This section addresses issues that have been found to be important for handling and installing precast concrete panels.

4.4.1 Trial Installation It is strongly suggested that a trial installation be performed prior to commencement of construction on-site, especially for projects that will be constructed within short construction windows such as overnight or weekend closures. The trial installation should be used to confirm and demonstrate the following, also shown in Figure 4.4.1-1:      

Base materials Base preparation procedures Handling and fit-up of the panels Overall sequencing for installation of the panels Manpower needs for each operation Equipment selection, management, and placement

Trial installations are particularly important for applications with complex geometry, and where grading the base to a precise cross-slope is required. The trial installation should include the assembly of three or more precast panels where a single panel forms all lanes and shoulders, or six or more panels where multiple panels are required across the travelled way. At least three panels should be assembled in each lane, to demonstrate fit in both the transverse and longitudinal directions. Joint epoxy and final post-tensioning should not be included in the trial installation, but the fit of the panels and alignment of the ducts should be checked. Materials and procedures for fit-up post-tensioning to compress the epoxy in the joints should be demonstrated to avoid unanticipated events during construction. Figure4.4.1-1 A Trial Installation is Shown being Conducted near the Project Site using the Same Personnel, Equipment, Procedures, and Materials as Planned for the Project.

4.4.2 Equipment and Mobilization Equipment to handle panels during installation must be selected based on the weight and dimensions of the precast concrete panels, and the staging restrictions for the particular site. Typically, a crane is used. Ideally, the crane should be positioned so that it is capable of installing at least two or three panels before needing to be reset. For single lane reconstruction projects, the crane will likely be staged just behind or on the previously installed panel. In this scenario, the crane’s outriggers should be positioned off of the newly installed panels whenever possible. The panels should also be visually inspected for apparent voids beneath them that may lead to cracking under the weight of the crane and outriggers. For two or more lanes, it may be possible to locate the crane to the side of the installation area. If it is necessary to stage the crane on the prepared base in front of the panels being 4 - 11

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installed, the outriggers or tracks should be properly supported so that they will not damage the prepared base. The base surface should provide adequate support for installation equipment. Any damage to the base must be repaired prior to installing panels. Rather than conventional cranes, other equipment options to lift and install the panels include front-end loaders with a spreader beam and travel-lifts that can straddle the lane(s) where the precast panels are installed. Such equipment requires less clearance outside of the edges of the installation, which may be necessary for single lane installations or installations with limited access outside of the pavement being replaced. Equipment that requires less overhead clearance, such as a front-end loader, may be necessary for installing panels beneath overpasses, sign bridges, and overhead utility lines. Figure 4.4.2-1 shows examples of equipment that have been used for PPCP projects. For projects needing complex maintenance of traffic lane closure sequences, a trial mobilization should be conducted prior to beginning actual construction. This trial mobilization can be used to identify issues in equipment mobilization and staging that may affect panel installation. The trial should be completed with the same conditions (time of day and location) as the actual project. Figure 4.4.2-1 Examples of Equipment used to install Pavement Panels

a) All-terrain Crane (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Crawler Crane

c) Mobile Crane

d) Front End Loader Document 4 - 12

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4.4.3 Panel Alignment 4.4.3.1 Horizontal Alignment Panel alignment is critical for ensuring that the pavement follows the intended roadway alignment and the posttensioning ducts align between panels. A deviation from the intended roadway alignment could be caused by an initial panel not set perpendicular to the centerline, which causes all subsequent panels to “creep” away from the intended centerline; or by variation in panel dimensions, even panels that are within tolerance. Misalignment requires that corrections be made. Because PPCP panels are clamped tightly together with post-tensioning, deviations in alignment cannot be corrected by intentionally leaving gaps between panels. Therefore, permanent shims are placed in the joint to vary its width at one end. As a rule, shims should only be used as a last resort for helping correct alignment because they result in permanently wider joints between panels. Such joints are susceptible to water penetration, grout leakage at post-tensioning ducts, and uneven distribution of the post-tensioning forces through the section. If shims are used, they should be limited to a thickness of ⅛ or ¼ in. Epoxy should be applied as thickly as necessary to fill the resulting open joint and help provide uniform contact between faces of the panels across the joint. Adjustments to the alignment of the PPCP section can also be made by laterally shifting or slightly offsetting individual panels. The amount of offset should be limited and can be determined from the size of post-tensioning ducts. The post-tensioning ducts should be selected to allow some small amount of offset. As a rule, panels should not be offset more than ½ in., assuming the post-tensioning ducts are large enough to accommodate a ½-in. offset. A more desirable alternative for correcting alignment would be to plan an open keyway joint between two or more panels in each post-tensioned section. The open keyways would permit a panel to be set at a slight angle to the previous panel to correct misalignment without the use of shims or offsets. The keyway would then be filled with a high-strength, rapid-setting grout mixture prior to post-tensioning, similar to open keyways that are used for bridge deck panels. This alternative would require splicing the post-tensioning ducts together through the open joint to ensure continuity of the duct, and may also require filling the keyway prior to opening to traffic. 4.4.3.2 Vertical Alignment The keyways at the panel joints prevent significant vertical misalignment. Tolerances for keyway dimensions will affect the potential amount of vertical deviation between panels. In general, vertical misalignment of up to ¼ in. can be expected, and is normally acceptable for opening to traffic until the precast pavement can be diamond ground to meet agency requirements for ride quality. Vertical alignment across longitudinal joints between adjacent sections of PPCP (e.g., between lanes) will primarily be controlled by grading of the underlying base. Careful attention to grading of the base should help limit differentials to ½ in. or less. If larger vertical differentials are observed, it may be necessary to remove the panels and re-grade the base. Any vertical differential at longitudinal joints between panels or lanes should be corrected in the final pavement with diamond grinding for safety reasons and to ensure proper drainage of water from the surface.

4.4.4 Panel Joints Epoxy used in the joints between panels is applied to both keyway surfaces prior to installing each panel. Epoxy should be applied primarily to the vertical faces of the keyway, but also is placed in the tongue and groove between the post-tensioning ducts. Epoxy should be kept at least ½ in. from the post-tensioning duct openings to prevent it from seeping into and potentially blocking the ducts as the panels are compressed together. The epoxy can be applied to the keyways while the panel is on the truck, just prior to being installed, or it can be applied to the keyways as the panel rests on the base, just prior to moving the panel into its final position. Excess epoxy that is squeezed out of the joint onto the top surface of the pavement (Fig. 4.4.4-1) should be scraped off immediately before it sets to eliminate the need for grinding it off later. When epoxy is not squeezed out the top of the joint, but there remains a slightly open joint, additional epoxy should be troweled into the joint from the top to completely seal it. If segmental duct couplers are not used, compressible foam gaskets should be installed around every posttensioning duct, as shown in Figure 4.4.4-1 to prevent epoxy from entering the duct and to prevent post4 - 13

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tensioning grout from leaking from the duct. The gaskets should be checked continually as the panel is moved into its final position to ensure that they have not shifted or fallen off. Ideally, gaskets should be glued in place to minimize the risk of them falling off. They can be glued well in advance of panel installation, saving time on site. Figure 4.4.4-1 Panel Joint Considerations

a) Epoxy Squeezed from the Top of the Joint

b) Compressible Foam Gaskets Adhered around each Duct (Both Panels)

4.4.5 Temporary Post-Tensioning Temporary post-tensioning pulls the joints between panels tightly closed as they are assembled. This helps to ensure a better seal between the panels and provides the required clamping force until the epoxy sets. It is not probable that the final post-tensioning force can be applied prior to hardening of the epoxy. This procedure also reduces the potential for incremental growth in the length of the pavement due to joints that are insufficiently closed. Temporary post-tensioning is accomplished using two post-tensioning tendons located at approximately the quarter- or third-points of the panel width, as shown in Figure 4.4.5-1. The number, size, and force applied to these tendons should be sufficient to provide a minimum clamping force of 30 psi (or the stress recommended by the epoxy manufacturer) across the panel joint for properly seating the keyways in the epoxy. The area over which the force is effective can be approximated by the panel length times the panel thickness. Temporary posttensioning can be done after each panel is installed, or after every two or three panels if it can be determined that doing so will provide satisfactory performance as required. Using strand tendons, the two temporary strands are fed into the ducts from the joint panels and fed through each panel as it is installed. The end of the strand in the joint panel is temporarily anchored in the post-tensioning pocket, while temporary bearing plates are placed against the keyway at the tensioning end of each tendon and the specified post-tensioning force is applied simultaneously to both tendons. If there is a wider gap at one end of a joint than the other, the stress levels in each tendon can be adjusted to try to close the wider end of the joint. After the force is applied and the joints have closed as much as possible, the force is relaxed and the strands are retracted slightly for ease of installation of the next panel. It has been shown that once the panels are drawn together, they will remain together when the force is relaxed. Depending on the temporary prestress force requirements, smaller strands (e.g., 1/2-in. or 7/16-in.-diameter) can be used since they are more flexible and easier to work with than 0.6-in.-diameter strands.

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Regardless of the size of strand used, they should not be stressed to more than 70 percent of ultimate strength. This is because there will be a number of locations along the strand with indented grooves from the teeth in the wedges of the anchoring chuck, which may weaken the strand. For the same reason, the temporary strands must not be used as the final post-tensioning tendons. The temporary strands should be removed and replaced with new strands prior to final post-tensioning. Epoxy-coated strand should not be used for temporary post-tensioning due to the need for multiple locations of anchorage along the length of the tendon. Bar tendons are an alternative to strand for temporary post-tensioning. An advantage of bar tendons is that they can be left in place and used as part of the final post-tensioning. Another advantage is that bar tendons can be tensioned and “locked off” with temporary anchor plates left in place prior to opening the pavement to traffic regardless of the number of panels that have been installed. This ensures the pavement slab is in compression when it is opened to traffic prior to final longitudinal post-tensioning. Temporary strand tendons will likely need to be removed prior to opening to traffic. Ducts for bar tendons are cast into the panels at approximately the quarter- or third-points of the panel width, typically replacing the strand tendons in those locations. The ducts must be large enough to accommodate the couplers used to couple the sections of bar together. High-strength, threaded post-tensioning bars are inserted into each panel prior to installation. The bars from the panel being installed are coupled to the bars protruding from the panels already in place and then tensioned (after each panel or every two or three panels) to pull the panels together and compress the joint(s). Care should be taken to ensure that the bars are perpendicular to the joint face when tensioned. Bars skewed even slightly can cause the panels to shift laterally when temporary posttensioning is applied. If epoxy coating is used, care should be taken to prevent damage to the coating on the bars and couplers during installation. Figure 4.4.5-1 Tensioning Temporary Post-tensioning Tendons

a) Temporary Strand Tendons

b) Temporary Bar Tendons

4.4.6 Mid-Slab Anchor The purpose of a mid-slab anchor is to keep the sections of PPCP from sliding longitudinally or laterally over time, while also forcing them to expand and contract outward from mid-length. This helps to ensure that the width of the expansion joint remains more uniform by controlling where movement can occur. The mid-slab anchor also helps prevent the section of PPCP from sliding laterally down a cross-slope, resulting in wider expansion joints or separation from shoulders that are not tied to the pavement. The anchors are steel rods driven through sleeves cast into “anchor panels” and through the base or driven through holes drilled through the bottoms of stressing pockets. Mid-slab anchors are shown in Figure 4.4.6-1. Ideally, mid-slab anchors should be installed prior to the final longitudinal post-tensioning to help ensure that the elastic shortening draws both ends of the PPCP section toward mid-slab. However, if the anchors are embedded in central stressing pockets or if construction constraints do not permit them to be installed prior to posttensioning, it is permissible to install them after post-tensioning. An exception is if the expansion joints are not 4 - 15

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opening uniformly during post-tensioning, it may be the result of not having the mid-slab anchors in place. In this case, it may be necessary to install mid-slab anchors prior to final post-tensioning, if possible. In any case, the anchors should be installed prior to diamond grinding for final ride quality. Figure 4.4.6-1 Mid-slab Anchors

a) Anchor Bar Drilled, Driven, and to be Grouted into Central Stressing Pocket (Photo: Merritt et al., 2002)

b) Anchor Bars Installed in Sleeves Cast into Panels

4.4.7 Under-slab Grouting The necessity for grouting voids beneath PPCP panels will depend primarily on the type of base material used and the precision to which the underlying base or level-up course is graded. PPCP panels tend to “settle” into more flexible bases such as asphalt or pervious concrete with a retarder, leaving fewer voids than less forgiving or rigid bases such as lean concrete or crushed stone aggregate. The extent of under-slab voids is not discernible by visual inspection during precast panel installation. Therefore, it is good practice to plan to install grout under the entire pavement. For this reason, ports through which to pump grout should be cast into the precast panels at a regular spacing (e.g., 3 to 4 ft) in both directions. If necessary, ports may also be drilled into the panels in the field. Cementitious grout has been used to fill under-slab voids, but other materials, such as proprietary urethane foams, are also available and have been used with great success for pavement under sealing and bridge approach slab restoration. Experience has shown that it is better to complete under-slab grouting prior to grouting the post-tensioning tendon in order to reduce the potential for tendon grout to leak beneath the slab. However, if under-slab grout is observed coming to the top surface of the slab, it may be necessary to complete tendon grouting first so that ducts are not filled and blocked by under-slab grout. Under-slab grout should essentially be fed by gravity flow, or pumped under very minimal pressure, less than 5 psi, to prevent it from lifting the slab or forcing grout to the top surface of the pavement. Under-slab grout should be pumped into a “downstream” or lower elevation port until it flows from an adjacent “upstream” port, or until the maximum pressure is reached. The process should continue until grout has been pumped into or flows out of all under-slab grout ports. The edges of the section being grouted should be sealed or backfilled to prevent grout from leaking from beneath the slab.

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Figure 4.4.7-1 Two Under-slab Grouting Techniques used for PPCP

a) Under-slab Grouting by Gravity Feed (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Under-slab Grouting by Low-Pressure Injection

4.4.8 Filling Holes and Pockets Proper filling of the post-tensioning pockets and lifting anchor recesses is critical to their performance and the overall performance of the finished pavement. For post-tensioning pockets, the surfaces of the pockets should be clean of grease, traces of asphalt, curing compounds, or other materials that may prevent the fill material from bonding to the surfaces. The surfaces should be wetted just prior to concrete placement or an epoxy bonding agent applied to the faces to improve bond. It is important to properly cure the concrete in these pockets. Ideally, wet mats or plastic sheeting should be used as long as possible, at which point a thick application (two coats) of curing compound should be applied prior to opening to traffic. For lifting anchors that result in large recesses, the recess should also be free of grease, curing compounds, or other deleterious materials that may prevent bonding of the fill material. If the lifting anchor itself shows signs of corrosion, the steel should be sandblasted to clear away rust just prior to placing the fill. For all larger lifting anchor recesses, an epoxy bonding agent should be applied to the face of the recess and to the steel lifting device to improve bond. The fill material must be properly cured with wet mats or plastic sheeting, and curing compound.

4.4.9 Other Considerations 4.4.9.1 Intermittent Traffic and Transition Slabs Most reconstruction applications require the PPCP to be opened to traffic between the allowable construction lane closures. Not all of the steps for PPCP construction described in this document need to be completed before the pavement can be opened to traffic. For example, final post-tensioning does not need to be complete prior to traffic as long as the temporary post-tensioning is in place and the panels appear to be reasonably well-supported. However, it is desirable to apply final post-tensioning as soon as possible after panel installation, preferably within 7 days. Another operation, tendon grouting, doesn’t need to be complete prior to traffic, even if final posttensioning has been completed. Grouting can be finished during subsequent construction operations, but preferably within 7 to 40 days, depending on the environment in which the project is constructed, as recommended in the Specification for Grouting of Post-Tensioned Structures ( PTI, 2003). Document 4 - 17

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Post-tensioning pockets cannot be filled until after final post-tensioning, but should be filled immediately after stressing whenever possible. Prior to post-tensioning, the pockets can be temporarily filled with cold patch asphaltic materials, or preferably, covered with steel plates or bolted-down steel covers that are nearly flush with the top surface of the panel. To provide for intermittent opening to traffic, transitions from the PPCP to the existing pavement will be required because an additional 2 to 3 ft of the existing pavement is typically removed to provide working space at the end of the new pavement. Steel plates may be used over a narrow transition, on the order of 1 to 2 ft long. For wider than 2-ft-long transitions, the void can be filled with cold patch material, timber mats, or temporary precast concrete panels as shown in Figure 4.4.9.1-1. Ultimately, the type of transition used will depend on the type of roadway, traffic volumes, posted speeds, and standard practices permitted by the owner agency. Figure 4.4.9.1-1 Temporary Precast Panel used to Fill the Gap between the End of the Precast Pavement and the Existing Pavement.

4.4.9.2 Incremental Changes in Pavement Length The joints between precast panels often are slightly wider than planned, effectively lengthening the overall pavement section from the sum of many joints. Usually, this is not a problem and, for reconstruction projects, will simply require removal of a small length of additional pavement. However, if the limits of a PPCP section are constrained by fixed points, such as a bridge structure abutments or change in existing pavement type, it may be necessary to:   

eliminate one or more panels, produce a smaller panel to fit between the PPCP and the structure (once the final limit of the PPCP can be determined with certainty), or permit a closure pour between the end of the PPCP and the structure.

Closure pours are often the simplest solution and will provide a more seamless transition from the PPCP to the existing pavement. However, if the project is constructed under a short closure, it will be necessary to use rapid strength gain concrete materials.

4.5 POST-TENSIONING PROCEDURES It is highly recommended that post-tensioning operations be completed by a specialty post-tensioning contractor with experience with single-strand and threaded-bar post-tensioning materials and practices, as applicable to the project. Post-tensioning field personnel should be certified through the appropriate Post-Tensioning Institute Field Personnel program, Bonded or Unbonded, Level 1 for workers and Level 2 for supervisors (PTI, 2012). The post-tensioning contractor and supplier should be involved in the project prior to development of shop drawings for the precast panels. This will help to ensure that the proper post-tensioning hardware is selected and detailed 4 - 18

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in the shop drawings and that the post-tensioning pockets are sized for the stressing rams that will be used. Separate shop drawings for the post-tensioning system should be submitted by the post-tensioning contractor for incorporation into the precast panel shop drawings. The post-tensioning contractor should also be involved in planning the construction sequence and schedule to ensure that provisions are made for all of the necessary steps in post-tensioning and grouting. Contractor personnel should all be given necessary safety training for working around post-tensioning operations prior to beginning construction.

4.5.1 Equipment and Mobilization Equipment for the post-tensioning operation includes the stressing rams (for strand or bar tendons), their corresponding pressure gauges and calibration charts, hydraulic pumps, mechanical strand pushers, and the grout mixing and pumping plant. “Banana nose” stressing rams (stressing rams with a curved snout) are commonly used for strand tendons in order to minimize the required size of the post-tensioning pockets. The post-tensioning contractor should be familiar with the use of these rams. Back-up equipment, particularly for the stressing rams and hydraulic pumps should also be supplied. Generators may also be required for running the hydraulic pumps, and a water truck may be required for cleaning up residual grout that leaks onto the pavement surface. Depending on the size of the project, all post-tensioning materials and equipment should be at the project site or nearby in a staging or storage area prior to beginning panel installation. This includes the equipment mentioned above, as well as post-tensioning strand or bars, bar couplers, anchor chucks and wedges (including those used for temporary post-tensioning), and temporary post-tensioning anchor plates. For panel installation, the stressing rams should be properly set up and readied for the temporary post-tensioning operation to ensure that temporary post-tensioning is applied in a timely manner after each panel (or group of panels) is installed. Dual rams should be set up for simultaneous stressing of the two temporary post-tensioning tendons.

4.5.2 Tendon Installation Post-tensioning tendons should either be supplied to the project precut to the proper lengths or cut to length on site well in advance of when they are needed. Strand tendons should include the necessary “tail” length for the stressing ram. Banana nose stressing rams will require a longer tail than standard stressing rams. Bar tendons must be cut to the length needed because any additional length will “grow” beyond the length of the pavement section as the panels are assembled. When using epoxy-coated strands, extra care must be taken to protect the epoxy coating from being damaged or abraded as the strands are inserted into the ducts. Wedges for epoxy-coated strand should be three-part wedges capable of “biting through” the coating and into the strand. Removal of the epoxy coating to allow the use of standard bare strand wedges must not be permitted. Bar couplers should include internal positive stops to help ensure each bar is fully threaded into the coupler. Removal of the epoxy coating from threaded bar tendons and couplers must not be permitted. Final longitudinal post-tensioning strand tendons can be installed after all of the panels for a section of PPCP have been installed, or fed sequentially into each panel as it is installed to help ensure there are no blockages. Depending on the size of duct and type of strand used, a mechanical strand pusher may be needed to feed the strands through all of the panels. However past experience has shown no problems with pushing strands by hand up to 250 ft. After the strands are in place, the wedges should be seated around the strand as tightly as possible prior to stressing. When transverse post-tensioning is used to tie adjacent sections of PPCP together, they should be inserted in the ducts, but not stressed, prior to longitudinal post-tensioning. This will ensure that the tendons are placed prior to any shifting or differential movement between adjacent sections that may occur during longitudinal posttensioning.

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4.5.3 Stressing Final Tendons The sequence for stressing the permanent tendons should be established prior to panel installation. In general, tendons should be tensioned starting at or near the centerline of the PPCP slab, progressing outward laterally, alternating to tendons on either side of the centerline, until all tendons have been stressed. Alternatively, if two stressing rams are available, two tendons (one on each side of the centerline) can be stressed simultaneously. However, should the epoxy not be fully set, any movement of the panels should be carefully monitored to ensure the joints between panels are closing uniformly. PPCP tendons are typically stressed to between 75 and 80% of their ultimate strength, but this may vary depending on the tendon type and prestress requirements from design. If a combination of bar and strand tendons is used, the bar tendons will typically be stressed to a force equivalent to that in the strand tendons, but not necessarily 75 to 80% of ultimate strength. Using conventional single-strand stressing rams, two to three sequential “pulls” will normally be required to reach 75% of the tendon ultimate strength, depending on the tendon length. When using epoxy-coated strand, the wedges should be checked after each “pull” to ensure they are not clogged with epoxy. Clogged wedges should be immediately replaced. When stressing from a central stressing panel, a “dogbone” anchor is used to couple the two halves of the strand tendon together. The tendon is tensioned through the dogbone anchor at the central stressing pocket, as shown in Figure 4.5.3-1. The dogbone anchor should be positioned at one end of the stressing pocket prior to stressing, so that it will move toward the middle as the tendon elongates. Prior to stressing, the wedges at both ends of the tendon should be hand seated into the fixed-end anchors. Figure 4.5.3-1 Central Stressing

a) Splicing Two Lengths of Tendon at a Central Stressing Panel using a Dogbone Anchor

b) Close-up of Dogbone Anchor in a Central Stressing Panel

For end stressing procedures (Fig. 4.5.3-2), each tendon is typically stressed from only one end. Longer tendons may require stressing from both ends due to losses in force from wobble and duct friction. To help ensure that the prestress force is more uniform over the entire length of a PPCP section, stressing should be alternated between tendons from one end of the section to the other.

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Figure 4.5.3-2 Examples of End Stressing from Pockets in the Joint Panels.

For final stressing of strand tendons when bar tendons are used for temporary post-tensioning, the strand tendons should be stressed first, followed by final stressing of the bar tendons (which should already be tensioned to the “temporary” stress level). The two bar tendons should be stressed simultaneously if possible. According to standard post-tensioning practice, the elongation of each tendon must be measured during stressing and compared with theoretically computed elongations corresponding to the applied tensioning force. As a standard practice, the tendon is tensioned to 20% of the final stress level, marked, and then stressed to the final stress level during which the elongation is measured. If measured elongations deviate more than 7% from those calculated, the discrepancy must be evaluated to determine the probable cause, according to the AASHTO LRFD Construction Specifications (AASHTO, 2010). One possible cause of discrepancy may be a miscalibrated jack. Jacks need to be calibrated before the start of the project and at a minimum every 6 months throughout the project. Transverse tendon stressing (if applicable) should not be completed until longitudinal post-tensioning has been completed (Fig. 4.5.3-3). Longitudinal post-tensioning may cause differential movement between adjacent sections of PPCP, after which the sections can be post-tensioned together transversely. Figure 4.5.3-3 Transverse Post-tensioning

a) Installing Transverse Post-tensioning Strands (Photo: Merritt et al., 2002)

b) Tensioning Transverse Strands

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.5 Post-Tensioning Procedures

4.5.4 Grouting Ducts Ducts should be grouted following established procedures for single strand (or single bar) post-tensioning ducts, and should be supervised by a grouting technician certified by the ASBI Grouting Certification Program ASBI, 2012). The Specification for Grouting of Post-Tensioned Structures (PTI, 2003) provides guidance for equipment and procedures for grouting tendons. It should be noted, however, that grouting practices must be modified for post-tensioning tendons used in PPCP. For example, it is seldom possible to achieve an air-tight, water-tight posttensioning duct system, especially without the use of segment joint duct couplers. This is due to the nature of the PPCP system, which uses nonmatch-cast panels and relies on compressible neoprene or foam rubber seals and epoxy in the joint to seal the post-tensioning ducts between panels. For this reason, it is not practical to pressure test the ducts before grouting. The manufacturer of prepackaged grouts should supply test results for properties of the grout, including setting time, strength, permeability, volume change, pumpability and fluidity, bleed, noncorrosive properties, and wet density. The grout should be proportioned with water and mixed according to the manufacturer’s recommendations based on the ambient conditions during grouting. Changes in proportioning beyond the manufacturer’s recommendations may require testing of these properties. Fluidity should be checked daily at the start of grouting operations and during the grouting after each time the pump is flushed. Fluidity should be checked in accordance with Standard Test Method for Flow of Grout for Preplaced-Aggregate Concrete (Flow Cone Method) (ASTM C939) using the modified test method for prepackaged thixotropic grouts. Efflux time for prepackaged thixotropic grouts should be between 5 and 30 seconds. Fluidity can be adjusted as necessary within the manufacturer’s limits to accommodate the conditions of the project. Grout should be pumped into the “downhill” end of each duct until it flows from an intermediate vent, or until a maximum permissible pumping pressure of 145 psi is reached. Once grout flows from an intermediate vent, the valve on that vent should be closed and pumping continued until it flows from each of the subsequent intermediate vents and finally the vent at the opposite end of the duct. Figure 4.5.4-1 shows pavement grouting in progress. If grout is observed leaking from a joint between panels or from underneath the slab, pumping should stopped and moved to an intermediate grout vent. Grouting should continue until grout flows from or is pumped into each grout vent and there is high assurance of complete tendon encapsulation. Grout leakage onto the surface of the pavement should be removed immediately so that it does not harden in place and affect the finished surface of the pavement. Grout that hardens on the surface may need to be removed with diamond grinding if it affects the riding quality of the pavement. Figure 4.5.4-1 Grouting Post-tensioning Ducts (Photos: Merritt et al., 2002)

a) Duct Grout Tube Extensions on the Surface of the Panels

b) Flush Grout Vents Ready to Accept Tube Extensions

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.6 Repairs and Surface Remediation

4.6 REPAIRS AND SURFACE REMEDIATION 4.6.1 Diamond Grinding Experience has shown that the ride quality of the as-installed PPCP surface is acceptable for intermittent opening to traffic during construction, and for lower speed roadways, but will likely not meet most agency specifications for high-speed roadways. Diamond grinding, also commonly used for cast-in-place concrete and asphalt pavements, is a cost-effective technique to achieve the more stringent requirements for ride quality. The pavement surface can be evaluated with a profilograph or inertial profiler to determine whether “spot grinding” will be able to bring the surface within specification limits, or whether a full blanket grind of the surface is required, as shown in Figure 4.6.1-1. Diamond grinding also provides a durable pavement texture that meets the requirements for skid resistance. However, a turf drag or broom finish texture should be applied during fabrication in order to ensure a skidresistant surface during intermittent openings, prior to diamond grinding. Design and detailing of the precast panels must provide adequate concrete cover above the reinforcement or post-tensioning ducts and hardware in the top of the precast concrete panels to account for the loss of the surface due to diamond grinding. Provisions should allow for grinding no more than ½ in. of concrete from the top surface of the panels. Figure 4.6.1-1 Diamond Grinding used to Ensure Compliance with Ride Quality Specifications

a) Diamond Grinding in Progress Across a Panel Joint

b) A Full Blanket Grind of a Concrete Pavement Surface

4.6.2 Damage Assessment Damage to precast concrete panels during handling and installation are typically addressed by agency inspectors on a case-by-case basis once the panels are installed. Of particular importance is damage to the top surface, which can affect ride quality and long-term pavement performance. Damage to the keyways that occurs prior to installation can affect installation of the panels. Isolated incidences during installation should be expected, particularly for large projects with numerous panels, but recurring damage or distress should be cause for discontinuing installation until the cause of the recurring damage can be determined and the problem mitigated. If fill concrete or grout is not properly installed in blockouts, lifting anchor recesses, or grout ports, it may work out under traffic or due to freeze-thaw cycles. If not repaired, these areas will likely continue to deteriorate over time, potentially affecting the riding quality of the pavement and its long-term performance. These areas should be repaired by removing the unsound fill material and replacing it with proper fill material. Sections 4.6.2.1 through 4.6.2.3 provide a summary of nonconformances that may occur during installation of PPCP panels. 4 - 23

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.6 Repairs and Surface Remediation

4.6.2.1 Spalls Spalling can occur during installation of the panels when they are moved too quickly and bump into each other. It often results in a corner spall or spall along the top surface of the keyway. Spalls may also occur during posttensioning if there are surface variations such as ridges or bulges of the keyways or if small incompressible debris is present in the joints between panels. These can lead to spalls along the top of the joint between panels when post-tensioning is applied. Figure 4.6.2.1-1 shows examples of spalls that can occur during construction. Surface Spalls―Surface spalls less than ¼ in. deep may not require repair, particularly if the pavement surface will be diamond ground. If the spalled area is larger than about 4 in. in diameter, and the surface will not be diamond ground, repair should be considered. Spalls greater than ¼ in. deep should be repaired. Panel Edge and Corner Spalls―Spalling of panel edges and corners that abut adjacent pavement or other PPCP panels should be repaired so that a durable joint is achieved. Spalling of the panel edges at an exterior edge or corner such as in the shoulder of the panel may not need to be repaired, at the discretion of the agency. Blockouts, Lifting Anchors, and Grout Port Fill Material―If spalling occurs around blockouts or the lifting anchor recesses during panel installation or post-tensioning, the areas should be repaired. Partial depth patching techniques described in Section 4.6.3 can be used to remove the spalled concrete and the repair can be made when the blockout or lifting anchor recess is initially filled. Figure 4.6.2.1-1 Examples of Spalling that may occur during Construction.

a) Mid-Panel Joint Spall (Note: Spalled Area Prior to Diamond Grinding on Right, and After Diamond Grinding on Left)

b) Corner Spall

c) Lifting Anchor Patch Spall (Note: the Edges and Perimeter of Anchor Patch Material have Spalled)

d) Spalled Corner Patch (Note: Corner had been Patched Prior to Panel Installation; Patch Spalled after Post-tensioning) 4 - 24

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.6 Repairs and Surface Remediation

4.6.2.2 Cracks Cracks that occur during construction generally appear during panel installation or shortly thereafter. They are typically caused by an uneven underlying base or by unsupported panel edges that cause the panels to bend or flex due to self weight and construction or traffic loads. Depending on the width of the crack and exposure conditions of the pavement, cracks observed in the panel surface may need further assessment to determine if they are shallow surface cracks or full-depth cracks. This may require core drilling through the panel using a 1- to 2-in.-diameter core drill at the location of the crack. Extensive occurrence of cracking should be cause for ceasing panel installation until the cause of the cracking can be determined and mitigated. Prestress and reinforcement in the panels should keep cracks held tightly closed. However, cracks observed during or just after construction should be carefully monitored over time to determine if they are growing wider, which will generally necessitate repair. Figure 4.6.2.2-1 shows various cracks that can occur during panel installation. Surface Cracks―Surface cracks include shallow longitudinal or transverse cracks, random cracks, and y-cracks. For projects constructed in aggressive environments with routine exposure to freeze-thaw cycles and deicing chemicals, surface cracks wider than 0.007 in. should be treated according to recommendations in the latest version of Control of Cracking in Concrete Structures (ACI 224R). For projects constructed in environments that do not include exposure to repeated freeze-thaw cycles and dicing chemicals, surface cracks wider than 0.012 in. should be treated. Epoxy injection should be used for repair of cracks exceeding these thresholds. Full-Depth Cracks―Full-depth cracks are generally oriented transversely or longitudinally. Full-depth cracks should be evaluated to determine the likely cause, as they may indicate a structural flaw in the pavement and can have a significant effect on pavement performance. If it is determined that a more serious structural flaw is not evident, epoxy injection can be used to repair the crack with the understanding that reoccurrence of the crack or additional cracking after repair may be cause for a more rigorous repair, such as partial-depth patching. Cracks at Filled Blockouts and Lifting Anchors―Cracks around the perimeter of a blockout or lifting anchor generally occur if the face of the blockout or lifting anchor recess is not properly wetted or painted with epoxy bonder prior to placing the fill material, or if the fill is not properly cured, resulting in shrinkage. The guidelines presented above for surface cracks should be used to determine whether treatment is needed based on crack width and exposure conditions. Figure 4.6.2.2-1 Examples of Panel Cracks that may occur during Construction.

a) Keyway Crack (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin) 4 - 25

b) Mid-Panel Transverse Crack (SEP 2012)

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.6 Repairs and Surface Remediation

c) Shrinkage Crack around Perimeter of Filled Stressing Pocket

d) Shrinkage Crack Around Perimeter of Filled Lifting Anchor

4.6.2.3 Corner and Keyway Breaks Keyway and corner breaks that occur during panel installation, usually from the panels bumping together, should be repaired. Severe corner breaks, which extend more than 3 ft along the length of the panel, may be cause for rejection of the panel. Keyway breaks longer than 25% of the length of the keyway may be cause for rejection of the panel. Figure 4.6.2.3-1 shows examples of keyway and corner breaks that can occur during construction. Figure 4.6.2.3-1 Examples of Keyway and Corner Breaks that may occur during Construction

a) Broken Keyway (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Corner Break

4.6.3 Repair Techniques Repairs to PPCP panels during construction require careful attention to the effect that repairs will have on the finished surface. Diamond grinding of the surface may remove minor surface defects (shallow spalls and cracks), 4 - 26

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.6 Repairs and Surface Remediation

but cannot correct larger defects such as deep spalls, corner, and keyway breaks. If the surface will be diamond ground, all repairs should be completed prior to grinding to ensure that the repair will not affect the final riding quality of the pavement. For shallow surface cracks, low viscosity sealing materials, such as methyl methacrylate can be used to fill the cracks through gravity flow or by toweling with a squeegee. For deeper and wider cracks, epoxy injection is commonly used. Epoxy injection uses pressure to force the epoxy into the extremities of the crack to bond the two sides of the crack together and seal it from water intrusion. For shallow spalls or indentations that require repair, epoxy-based mortar materials can be used to fill these areas, but should be inspected after diamond grinding to ensure the repair is sound. Partial-depth repair techniques are commonly used to repair deep surface spalls, edge spalls, keyway breaks or corner breaks, as shown in Figure 4.6.3-1. For partial-depth repairs, clean saw cuts should be made a minimum of 2 in. deep into the surface, edge, or keyway just beyond the extent of the damaged area. Saw cuts in the top surface of the panel should not form corners with angles less than 90 degrees in order to reduce the risk of reentrant cracks propagating from these corners. Alternatively, a 1- to 2-in.-diameter core drill can be used to form the corners of a repair area, with straight saw cuts between the core holes. After saw-cutting, all unsound concrete material should be removed, using only a lightweight chipping hammer if necessary. For deep edge spalls, keyway or corner breaks deeper than 2 in. that are repaired prior to installing the panels, it may be necessary to drill and epoxy No. 3 or No. 4 reinforcing bars into the panel to help anchor the patch in place. This reinforcement should be positioned so that proper concrete cover is provided after the patch is placed. Epoxybased patching materials have been used with good success for partial-depth patches. Surface repairs can be made across joints (i.e., over more than one panel), but only after post-tensioning has been completed. Care should be taken to not damage post-tensioning tendons when performing repairs. It is important that repaired areas on the keyways made prior to installation be properly finished and ground as necessary to ensure that the repair does not protrude from the plane surface of the keyways, preventing mating keyways from fitting together. Repairs should not cause the keyway or other surfaces to exceed tolerances. Figure 4.6.3-1 Examples of Keyway Repairs to Panels Damaged during Construction

a) Damaged Area Saw Cut and Cleaned for Patching (Photo: David Merritt, Center for Transportation Research, University of Texas at Austin)

b) Repaired Keyway Prior to Diamond Grinding

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.7 Final Inspection/4.8 Resources for Additional Information

4.7 FINAL INSPECTION 4.7.1 Responsibility for Inspection Final acceptance inspection of the pavement should be conducted following any necessary repairs and after diamond grinding. Responsibility for inspection throughout construction lies with the owner agency. The inspector should be familiar with key differences between PPCP and conventional concrete pavement construction, including all steps of the post-tensioning and grouting operations.

4.7.2 Key Inspection Items Inspection should document the as-constructed condition of the pavement for comparison with future condition surveys. This includes documentation of visible nonconformances and repairs of nonconformances. Items to be documented include cracks, spalls (particularly at joints between panels), and any deterioration of fill material in lifting anchors and blockouts. Documentation should include the condition of joints in the pavement. Any joints that are open or have obvious vertical differential across them should be documented for comparison with future condition surveys. The condition and width of longitudinal joints between adjacent PPCP sections and any joints between PPCP and adjacent existing pavement should also be documented for future comparisons. Expansion joint seals should be inspected to check that they are properly installed and bonded to both edges of the expansion joint. Finally, smoothness and ride quality should be documented initially and monitored over time. Smoothness can be measured with a profilograph, while ride quality should be measured with an inertial profiler.

4.7.3 Optional Inspection and Documentation In addition to the items for inspection in Section 4.7.2, other as-constructed condition items to consider for inspection and documentation include deflection testing and joint movement. Deflection testing is conducted to measure load transfer between individual panels and across expansion joints, as well as to determine if there are voids beneath the precast pavement. Load transfer between individual panels should be in the range of 90 to 100%. Load transfer across expansion joints, however, may be significantly lower than that of conventional jointed concrete pavement. This is primarily due to the fact that load transfer is provided solely by the dowel bars and underlying base across a joint that is typically much wider than conventional jointed concrete pavement. There is no contribution from aggregate interlock, as with conventional pavement. In addition to load transfer, deflection testing can provide some indication of whether voids are present beneath the PPCP. Deflection testing for voids is normally conducted at mid-slab or mid-panel locations, away from joints. High deflections generally indicate the presence of voids, but do not necessarily indicate the extent or depth of a void. For comparison, adjacent cast-in-place pavements can be tested to determine typical deflections based on the type of underlying subgrade. However comparisons with cast-in-place pavement must consider variations in type and thickness of the base and the slab thickness. Monitoring expansion joint movement will provide an indication of whether the expansion joints are functioning properly. Expansion joints should open and close with both daily and seasonal temperature cycles. No change in width may indicate a joint that is “locked” and not functioning properly, which can result in cracking adjacent to the expansion joint. Similar rates of movement among the various joints of a particular project indicate that the various post-tensioned sections are moving independently and the mid-slab anchors are functioning properly. However, the movement of the ends of the two post-tensioned slabs at each expansion joint should also be monitored to ensure the post-tensioned sections on both sides of the joint are moving and not just one side.

4.8 RESOURCES FOR ADDITIONAL INFORMATION An online compilation of resources for additional information on precast concrete pavement has been assembled by PCI, and is available at the internet address below. This site will be continually updated as new information becomes available from current and future projects. http://www.precastconcretepavement.org

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CONSTRUCTION OF PRECAST CONCRETE PAVEMENTS 4.9 Cited References

4.9 CITED REFERENCES AASHTO. 2010. AASHTO LRFD Bridge Construction Specifications, 3rd Edition with 2010 and 2011 Interim Revisions. American Association of State Highway and Transportation Officials, Washington, DC. 626 pp. https://bookstore.transportation.org/Item_details.aspx?id=1583 (Fee) ACI Committee 224. 2001. Control of Cracking in Concrete Structures, (ACI 224R-01), American Concrete Institute, Farmington Hills, MI. 46 pp. http://www.concrete.org/BookstoreNet/SearchResults.aspx?CATEGORY=271899&SEARCH_STATUS=ACTIVE (Fee) ASBI. 2012. Grouting Certification Program. American Segmental Bridge Institute, Buda, TX. http://www.asbi-assoc.org/index.cfm/grouting/training ASTM A882. 2010. Standard Specification for Filled Epoxy-Coated Seven-Wire Prestressing Steel Strand (ASTM A882/A882M – 04a). ASTM International, West Conshohocken, PA. http://www.astm.org/search/site-search.html?query=A882 (Fee) ASTM C939. Standard Test Method for Flow of Grout for Preplaced-Aggregate Concrete (Flow Cone Method) (ASTM C939). ASTM International, West Conshohocken, PA. http://www.astm.org/Standards/C939.htm (Fee) Merritt, D. K., B. F. McCullough, and N. H. Burns. 2002. Construction and Preliminary Monitoring of the Georgetown, Texas Precast Prestressed Concrete Pavement. Research Report No. 5-1517-01-1. Center for Transportation Research, University of Texas at Austin, Austin, TX. http://www.utexas.edu/research/ctr/pdf_reports/5_1517_1.pdf PTI. 2003. Specification for Grouting of Post-Tensioned Structures, Second Edition, (PTI M55.1-03). PostTensioning Institute, Farmington Hills, MI. 60 pp. http://www.post-tensioning.org/Uploads/2012_forWeb%20(low-res).pdf (Fee) PTI. 2012. Post-Tensioning Institute Workshops and Personnel Certification Programs include: Level 1 Unbonded PT―Field Installation Level 1&2 Bonded PT Field Specialist Post-Tensioning Institute, Farmington Hills, MI. http://www.post-tensioning.org/certification_program.php

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