Determination Of Setting Time Of Hydraulic Cement

DETERMINATION OF SETTING TIME OF HYDRAULIC CEMENT

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HYDRUALIC CEMENT

It is a type of cement that sets very quickly and hardens with the addition of water to the finely ground cement. It is the most commonly used cement at present. Nowadays, usually different blends of modern Portland cement are commercially referred to as hydraulic cement. It is composed of hydraulic calcium silicates. Hydraulic cement is a non-corrosive, nonrusting and non-shrink substance widely used in construction. This type of cement is especially good for structures that are constantly in contact with water because it is impermeable to water.

Types of Hydraulic Cement The three main types of cement that are most commonly used are Portland, blended and hydraulic, but Portland and blended cements are actually hydraulic cement. In fact, most types of cement used in construction are hydraulic.

1. Hydraulic cement: Type GU: General Use Type HE: High Early Strength Type MS: Moderate Sulfate Resistance Type HS: High Sulfate Resistance Type MH: Moderate Heat of Hydration Type LH: Low Heat of Hydration

2. Portland cement: > Type I, Type IA : general purpose cements > Type II, Type IIA : contain no more than 8% tricalcium aluminate > Type III, Type IIIA : similar to Type I but has higher early strength > Type IV : develops strength over longer periods of time, used in special type of structures that require heat to be generated from hydration > Type V : high sulphate resistance, contains no more than 5% tricalcium aluminate

3.

Blended cement:

Type IS (X): Portland blast furnace slag cement Type IP (X): Portland-pozzolan cement

How Hydraulic Cement Works? Hydraulic cement’s working principle is based on the process of hydration, which means the product hardens when water is added. Certain substances present in hydraulic cement initiate reactions due to the application of water, causing the mixture to set and harden very quickly with reduced curing time. The nature of these chemical products makes hydraulic cement impervious to water damage and further chemical attacks. Hence, this type of cement is suitable for construction of structures in close contact with or submerged in water.

When to Use Hydraulic Cement?

The right type of cement is to be selected based on the nature of the construction work. Different blends of hydraulic cement contain varying ratios of chemical components to suit specific needs. Hydraulic cement is highly suitable for projects that require quick setting and less curing time. However, it only gives a short window of time to work with it before it hardens, so it is recommended to apply hydraulic cement only for projects that can be done in 10-15 mins with a moderate amount of cement mix prepared at a time. Its ability to provide strength is immense, so hydraulic cement can be used for the construction of highly durable structures. The cement is not flexible, so it can only be used to provide mechanical support to structures.

For constructing underwater structures, hydraulic cement has almost no alternative. Being impermeable to water, it can be used in constructing structures that are in constant contact with water. This type of cement does not corrode or rust, hence it retains its strength even when submerged in water. It is also extremely useful for water-proofing. If the construction requires high durability but the location is in an extremely cold climate or on a frozen surface, applying hydraulic cement is not commendable in such circumstances unless certain measures are taken to ensure durability. Hydraulic cement does not shrink like normal cement, and some blends even expand upon hardening. This type expanding hydraulic cement is very useful for sealing concrete leaks and repair work. Sealing cracks with hydraulic cement will hold for many years, but it is not a permanent fix. For very fine cracks, caulk might be a better solution than hydraulic cement. Again, hydraulic cement will not solve problems caused due to condensation and not leaking.

Hydraulic Cement Uses

Hydraulic cement is very useful for the construction of:  Footings and foundation  Heavy construction  Walls, floor, stairway  Levee walls, sea walls, retaining walls  Bridges, culverts

 Posts, fence and fence posts, mileposts, electric  Monolithic concrete houses, poles, telephone poles concrete block houses  Curb and gutters  Tower substructures  Coefficient of expansion in  Dams, breakwaters concrete  Sewers  Columns and pillars  Electric ducts  Fountains  Water pipes  Waterproofing  Irrigation ditches, filter beds  Prison cells  Cisterns, reservoirs  Chimneys  Road foundations, paved roads,  Fire proofing, fire tests sidewalks  Sealing cracks  Tunnels  Adhesive for building  Railroads, ties, turntables, blocks  Abutments, fortifications

trestle belts

Hydraulic cement is also used for various specialized purposes.  Foundation repair

 Basement crack repair  Basement leak stopper  Repair Cracks in Concrete Walls, Floors, and Driveways

How to Apply Hydraulic Cement Proper use of hydraulic cement for maximum benefit include the following steps: Preparation  The surface on which the cement is to be applied should be clean. Dirt, oil, grease and loose particles will prevent the cement from adhering to the surface properly.  It is imperative for the temperature to be maintained between 45°F (7°C) and 90°F (32°C) during initial curing since the cement will not be durable on frozen surfaces.  The area should be saturated for 24 hours before applying cement there.  Small cracks and holes should be enlarged prior to the cement application. V-shaped cuts are to be avoided.

Mixing Cement  A mechanical mixer with rotatory blades is recommended for mixing the cement to get a uniform mix.  The mixer should be saturated and drained of excess water prior to mixing.  Following the manufacturer’s instruction, the required amount of water is to be added to the proper amount of dry hydraulic cement. However, once it begins to set, water should not be added anymore.  It is recommended that small amounts of cement be mixed at a time since it hardens very quickly and has to be placed within 10-15 minutes.  The cement mix should be blended at a relatively low speed.

Applying Hydraulic Cement  The hydraulic cement mix should be applied as quickly as possible.  Excessive blending will cause bleeding and segregation.  Any other additives or admixtures should not be added unless mentioned in the manufacturer’s instructions.

DETERMINATION OF SETTING TIME OF HYDRAULIC CEMENT

Cement paste setting time is affected by a number of items including: cement fineness, water-cement ratio, chemical content (especially gypsum content) and admixtures. Setting tests are used to characterize how a particular cement paste sets. For construction purposes, the initial set must not be too soon and the final set must not be too late. Additionally, setting times can give some indication of whether or not a cement is undergoing normal hydration.

Normally, two setting times are defined:  Initial set. Occurs when the paste begins to stiffen considerably.

 Final set. Occurs when the cement has hardened to the point at which it can sustain some load.

Both common setting time tests, the Vicat needle and the Gillmore needle, define initial set and final set based on the time at which a needle of particular size and weight either penetrates a cement paste sample to a given depth or fails to penetrate a cement paste sample. The Vicat needle test is more common and tends to give shorter times than the Gillmore needle test.

This test method covers the determination of the time of setting of hydraulic cement paste by means of the Gillmore needles.

Gillmore Needle Test

The values stated in inch-pound units are to be regarded as standard. The SI units, regarded as standard in ASTM C266, are provided for informational use only with regard to the original direction of mathematical conversion; as such, the inch-pound units are shown in parentheses. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Gillmore Needle Apparatus

Time of Setting of Hydraulic Cement by Vicat Needle

These test methods determine the time of setting of hydraulic cement by means of the Vicat needle. Two test methods are given; Method A is the Reference Test Method using the manually operated standard Vicat apparatus, while Method B permits the use of an automatic Vicat machine that has, in accordance with the qualification requirements of this method, demonstrated acceptable performance.

Apparatus

Vicat Needle Test

1.

Vicat apparatus: It consists of a frame, bearing a movable rod, weighing 300±0.5g, and having either: • A removable needle, 1mm in diameter, for finding out the initial setting time, or • A needle, 5mm in diameter for determining the final setting time.

2.

Conical hard rubber ring having 40 ± 1 mm height, inside diameter at the bottom of 70 ± 3 mm and inside diameter at the top of 60 ± 3 mm.

3.

Sensitive Balance.

4.

Paste mixer.

5.

Graduated glass cylinder.

6.

Glass plate with adequate dimension.

7.

Small trowel.

8.

Stopwatch.

Test Procedure  Weight out 500g of cement and place it on the mixing plate.  Form a crater in the center and add a measured quantity of water (the percentage of water obtained from normal consistency test).  Turn the material at the outer edge into the center within 30 sec. of time by the aid of the trowel.  After an additional interval of 30 sec. for absorption of water, complete the process by continuous vigorous mixing. Squeeze and kneading with hands for (1.5 min.).  With the hands quickly form this paste into a ball, complete the process by tossing the ball six times from one hand to the other hand, keeping the hands about 6 in. (15 cm) apart.  Press the ball, resting in the palm of one hand, into the large end of the conical ring of Vicat apparatus which held by the other hand.  Fill up the conical ring and remove the excess at the large end by a single movement of the palm of the hand.

 Place the ring on its large end on a glass plate and slice off excess paste at the smaller end at the top of the ring by single oblique stroke of a sharp edged trowel held at a slight angle with the top of the ring, and smooth the top if necessary, but never compress the paste during these operations.

 Place the ring with the paste under the rod of the Vicat apparatus, bring the initial setting needle (1mm) in contact with the surface of the paste, and set the scale to read zero or read the initial reading. This must not exceed 30 seconds after completion of mixing.  Release the plunger immediately and allow the needle to settle for 30 s. Determine the penetration of the 1-mm needle every 15 min until a penetration of 25 mm or less is obtained (Make each penetration test at least 5 mm away from any previous penetration and at least 10 mm away from the inner side of the mold).  Record the results of all penetration tests and, by interpolation, determine the time when a penetration of 25 mm is obtained. The elapsed time between the initial contact of cement with water and the penetration of 25 mm is the Vicat time of setting or Vicat initial time of setting.

 Set the (5 mm) diameter needle on the lower end of the rod. Determine the Vicat final time of setting end point to be the first penetration measurement that does not mark the specimen surface with a complete circular impression.  The elapsed time between the initial contact of cement and water and the end point determination above is the Vicat final time of setting.

Vicat Needle Apparatus

Vicat Needle Machine Test

The Vicatronic apparatus provides a completely automatic method for determining the initial and final setting time of cements or mortar pastes. The automated test operation provides for precise and repeatable results, which are automatically printed out from the integral printer built into the apparatus. The Vicatronic can also be connected to a PC via a RS232 cable allowing data to be downloaded via programs like Microsoft hyper terminal. The Vicat-Win software (H-3052.4) allows the receiving, managing, processing and completing test data; the software can automatically create graphs, personalize them and print test reports.

The Vicatronic has a large high-contrast, high-resolution LCD display, which shows the test data together with the general functions of the unit. The easy-to-see menu provides a simplified guide to running a test. During the test, the display also provides a real-time graph of the results, which can be monitored. The Vicatronic is supplied with firmware that allows the automatic performance of tests in accordance with the following standards: ASTM C191, AASHTO T131, EN 196/3, DIN 1164, DIN 1168 gypsum, NF P15/431 and BS4550. Additional programs can be developed by the operator. This is particularly useful when testing new mortars, additives or research tests requiring sophisticated and flexible applications.

The Vicatronic is supplied complete with the integral printer, two hardened needles (one with 1mm diameter and one with 1.13mm. diameter), two conical molds EN and ASTM, and a glass plate to hold the conical mold. Dimensions: 15.75" x 7.87" x 18.5” (400 x 200 x 470mm).

Vicat Needle Machine Test

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