Rammed Earth

INDEX INDEX...................................................................................................................................................................... 2 1. INTRODUCTION ................................................................................................................................................. 1 1.1.

MOTIVATION ......................................................................................................................................... 1

1.2.

OBJECTIVES .......................................................................................................................................... 2

1.3.

WORK SCHEDULE ................................................................................................................................ 2

2. STATE OF ART: EARTH AS A BUILDING MATERIAL ........................................................................................ 3 2.1.

EARTH BUILDING TECHNIQUES .......................................................................................................... 3

2.1.1.

BRICKWORK ................................................................................................................................. 4

2.1.2.

STRUCTURE .................................................................................................................................. 8

2.1.3.

MONOLITHIC ............................................................................................................................... 12

2.2.

EARTH BUILDINGS AROUND THE WORLD ........................................................................................ 21

2.3.

RAMMED EARTH STANDARDS .......................................................................................................... 27

2.3.1.

DEFINITIONS............................................................................................................................... 27

2.3.2.

HISTORY OF BUILDING CODES.................................................................................................. 28

2.3.3.

OVERVIEW OF EXISTING EARTH BUILDING STANDARDS AND NORMATIVE DOCUMENTS .. 34

2.3.4.

STANDARDS ABOUT BUILDING WITH EARTH AROUND THE WORLD .................................... 35

2.3.5.

COMMENTS ................................................................................................................................ 38

2.3.6.

SPANISH CODES ......................................................................................................................... 38

3. DISCUSION ABOUT RAMMED EARTH AS THE BEST earth building tecnique ............................................. 40 3.1.

ENERGETIC COST AND ENVIRONMENTAL IMPACT ......................................................................... 40

3.2.

PHYSICAL AND CHEMICAL PROPERTIES ...........................................................................................41

3.3.

TEXTURES OF EARTH ......................................................................................................................... 43

3.4.

RECYCLING EARTH AND EXTREME CLIMATES ................................................................................. 45

3.5.

THE FUTURE OF RAMMED EARTH .................................................................................................... 47

3.5.1.

PREFABRICATION ...................................................................................................................... 47

3.5.2.

ADDITIVES AND SPECIAL TREATMENTS ................................................................................... 48

4. SOIL TESTING ................................................................................................................................................. 60 4.1.

TRADITIONAL SOIL TESTING ............................................................................................................. 61

4.2.

MODERN SOIL TESTING..................................................................................................................... 70

5. SIMPLE COMPRESSIVE STRENGTH TESTS ..................................................................................................... 71 5.1. 5.1.1.

PARTICLE SIZE DISTRIBUTION .......................................................................................................... 72 Introduction ............................................................................................................................... 72

5.1.2.

Tests’ table ................................................................................................................................. 75

5.1.3.

Grain size distribution: conclusions ........................................................................................... 75

5.2.

ATTERBERG LIMITS AND OTHER PARAMETRES .............................................................................. 76

5.2.1.

Introduction ............................................................................................................................... 76

5.2.2.

Tests’ table ................................................................................................................................. 77

5.2.3.

Atterberg limits and other parameters: conclusions ............................................................... 78

5.3.

ADDITIVES .......................................................................................................................................... 78

5.3.1.

Tests’ table ................................................................................................................................. 78

5.3.2.

Additives: conclusions ............................................................................................................... 79

5.4.

METHOD OF PREPARING SAMPLES.................................................................................................. 81

5.4.1.

Tests’ tables................................................................................................................................ 81

5.4.2.

Method of preparing samples: conclusions ............................................................................. 82

5.5.

STORAGE CONDITIONS OF SAMPLES UNTIL THE STRENGTH TEST ................................................ 83

5.5.1.

Tests’ table ................................................................................................................................. 83

5.5.2.

Storage conditions of samples until the strength test: conclusions ....................................... 83

5.6.

CHEMICAL AND MINERAL COMPOSITION OF EARTH ..................................................................... 84

5.6.1.

Introduction ............................................................................................................................... 84

5.6.2.

Tests’ tables................................................................................................................................ 85

5.6.3.

Chemical and mineral composition of earth: conclusions ....................................................... 86

5.7.

DENSITY AND MOISTURE CONTENT OF SAMPLES .......................................................................... 86

5.7.1.

Tests’ table ................................................................................................................................. 86

5.7.2.

Density of samples: conclusions ............................................................................................... 88

5.8.

COMPRESSIVE STRENGTH ................................................................................................................. 89

5.8.1.

Introduction ............................................................................................................................... 89

5.8.2.

Tests’ table ................................................................................................................................. 90

5.8.3.

Compressive strength: conclusions .......................................................................................... 92

6. SIMPLE COMPRESSIVE TEST AT THE WIL ..................................................................................................... 94 7. BIBLIOGRAPHY ............................................................................................................................................. 106

AKNOWDLEGEMENTS This work symbolizes the end of an era in my life. Besides its intrinsic value for the hours and effort spent, it is the final seal of my first university degree. For this, first I have to thank the people who made it possible to reach this far, morally and economically: my family. They have given me the opportunity to be trained as a professional in one of the most prestigious universities in the country and also in my final year, and they have made possible an unforgettable experience as an Erasmus student in the wonderful city of Warsaw. And most importantly, to have a happy life full of opportunities and dreams fulfilled. To all my friends from Valencia, Paiporta, classmates, high school and university. Emancipate adventure in a new country, it is one of the most interesting experiences that a student can do because, with the role of student life always has a learning perspective, hungry to know and understand that let you absorb every moment that life gives you as if it were your last day. In this adventure I have met wonderful people, I have never felt alone, always wrapped by a large family of friends from many different parts of the world, supporting each other. And even, many great friends that have given to me more than I could never give to them back. I do not forget my teachers, those people we take example and wisdom and gradually shape our way of seeing the world. In particular I have to mention Mª Jesús Ferrando, my professor of philosophy at 2nd year of Bachillerato, which helped me to understand the world and realize the path I wanted to take in life. Although this has been maturing in my head over the years, I'm sure she planted many seeds. Also Pep Ballester, my math teacher also in 2nd year of Bachillerato: civil engineer, great teacher admirable for their professionalism and dedication to students, and a person with a big heart. Also the great Armando, a professor at the academy that helped me overcome two of the most difficult subjects of the degree, besides having one of the best attitudes to life that a person can have. At the Universitat Politècnica de València I have had very good teachers: Joaquín Cerver Montalva, Carmona Miguel Angel Carrión, Eduardo Hernandez Albentosa, Nacho Paya, Boquera Pascual, Miguel Angel Eguíbar, and so on. But I must mention especially MªTeresa Pellicer, for being my mentor in the project and Pedro Calderon, also always willing to help me with this work. At the University Politechnika Warszawska I had a warm welcome since the first moment. I must especially thank the attention given by Dr. Paweł, Erasmus coordinator, and his secretary Natalia Mochtak, both have helped us in our adaptation to the new university. To my English teacher Mrs. Wiesława Barnas, a lovely and great professor. Finally and most importantly, my project cotutor Professor Piotr Narloch, that opened my eyes to the possibilities of sustainable construction and has constantly been helping and supervising my work. I must also thank my student colleagues in the foreign university, the laboratory technicians and library workers. I hope this study will be useful to the work of Professor Narloch in his arduous task of drafting a standard on rammed earth for Poland as well as being useful for anyone interested in the subject, trying to contribute their grain of sand in the field of sustainable construction, which is definitely the way forward for civil engineering and architecture unless we want to condemn us to extinction.

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PROLOGUE In the South, more than one billion people do not have a close to minimum housing standards. They also have only the import of most known technologies and materials from developed world, which result in unaffordable costs of materials and construction methods. In fact, in some African countries, it is estimated that 90% of payments for the provision of construction materials are imported. This excess means paying exorbitant amounts of foreign currency that countries cannot cope in almost complete state of economic ruin. Besides, we think that the laying of different materials and construction methods require auxiliary tools and machines that must also be imported. From the social point of view, this situation alienates the masses of any housing solution with minimal living conditions, which is the true tragic dimension of the problem, thus complying huge pockets of marginalization in the belts of large cities, planned and built according to the model of North countries. This is evident in many cities in Latin America, for example. [1] Although slums and informal urban areas provide a crucial mechanism for the dwelling of many of the urban poor and disadvantaged, they pose a range of serious humanitarian and environmental problems for both present and future generations, including:      

Environmental deterioration and life-threatening problems related to sanitation and pollution (including air and water pollution from garbage and sewers) Exposure to environmental hazards (landslides, flooding, poor drainage) Further health risks, diseases and injuries related to poor construction, overcrowding, antisocial behaviour and crime Uncontrolled and conflictual urban sprawls Informal and extra-legal economies Illegal and harmful infrastructural connections

Through both of these functions, housing represents a system of social and material relationships, which is simultaneously arranged at the different spatial scales (homes, surrounding neighbourhoods, settlements, regions, countries) and which, therefore, requires a corresponding hierarchy of policy interventions. [2] But, ¿what if this countries have already got the properly materials and simply need to acquire new construction methods that allow them to move forward in good quality housing with their own resources? Earth construction have been the first building material around the world. But we just cannot keep constructing big cities like we used to do 10.000 years ago. We have already achieved great advances in earth construction methods to adapt it to the current quality of life, and we have to share them, especially with this poor countries which need it, furthermore, we owe them because of the ecological debt. The ecological debt is the debt accumulated by the North to the South for two reasons. First, by exports of primary products at very low prices, i.e. excluding environmental damage at the site of the extraction and processing, and global pollution. Secondly, for free or very cheap occupation of environmental space-the air, water, the earth to deposit the waste produced by the North. Ecological Debt has originated under colonialism and continues to be generated each day. The concept of ecological debt is based on the idea of environmental justice: if all the world's inhabitants are entitled to the same amount of resources and the same share of environmental space, which use more resources and take more space have a debt to the other. [3]

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Do not forget to mention some large construction programs that embrace these principles promoted by governments, especially in Latin America (Peru, Mexico, Colombia, Cuba ...) or activity groups in developed countries as CRATerre in France, the Agency for Cooperation (GTC) in Germany and the University of Kassel; and the Instituto Eduardo Torroja in Spain with his very low cost Housing Projec, or the program Proterra by CYTEC. Likewise, we must also highlight the efforts of many non-governmental organizations (NGOs) and the interest of professionals in architecture running many construction projects with unbaked earth and performing this research and dissemination of the material. The grotesque dimension of the problem arises when in countries suddenly enriched by oil, for example, the materials and construction methods used always disappear quickly, as happened with our vernacular architecture, to make way for the ineffable copy of archetypes and technologies imported outside that, despite their obvious climate maladjustment, willingly they use as a sign of social distinction. Technology transfer has always existed, but whereas in the past was carried out by slow adaptation processes currently acquires unmistakable features of speed, massive and unidirectional. We must therefore encourage a selective transfer, but not indiscriminate, which serve mainly to help an autonomous technology research policy. [1] On the other hand, the lack of regulation in our country often makes that building with earth, especially the technique of rammed earth, has a minority use in heritage restoration, always resorting to the easy from the point of legally in new buildings, leading to the widespread use of the most damaging environmental techniques. Despite this is out of the reach of this work, we also may mention that taking care about the environment has a lot of fields to be treated as well as construction techniques. The use of renewable energies has to increase, moreover the economic barriers. And far more important is the fact that the agriculture system is failing to feed the entire population of the world. It is destroying ecosystems while we need to plant grain and soya to feed this farm animals over the native woods and flora. It is also contributing to increase the level of greenhouse gases in greater level than oil industry, and many other facts that are putting under risk our planet [4]. In conclusion, what Bio-Construction means is more than we could think in first instance. The model of EcoVillage should include unless three factors: sustainable construction, sustainable agriculture and sustainable energy sources.

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1. INTRODUCTION 1.1.

MOTIVATION

I never found a true vocation for engineering during school. I liked the challenge posed to study a difficult degree, with a lot of mathematical and physical subjects, which are the subjects I most enjoyed during my high school studies. Over the years I realized that engineering was losing its pure mathematics component and was transformed into a pragmatic science, full of approximate models, assumptions or "magic formulas". This disenchanted me even more and got to wonder seriously quit university and focus on other fields such as music, one of my great passions in life. But the inertia and stubbornness allowed me to reach the end of the road. I like to finish things I start, and I knew that engineering could open up a thousand doors to different types of work in many different areas. Therefore, there was no point leaving, and less after spending the first three years of college that are really hard. Finally, in the fifth grade I chose the specialty of civil constructions. Again by inertia, as required by yourself and not by vocation. Because as I say, I never had a real engineering vocation. However, everything changed when I came to Poland. I started my Erasmus in Warsaw in late September 2014. I arrived at the Technical University of Warsaw and after the first few weeks of adaptation to the classes and the new environment my mission was to find a theme and a mentor for my final project. I've always been an ardent defender of the environment and human rights, so with some idea in my head about it, I started talking to Dr. Paweł Nowak, the Erasmus coordinator who did the welcome speech. I mentioned my concerns and he borrowed me a book written by him: “Sustainability in Construction”, plus recommended me some teachers to talk about these issues, as they were more stuck in this field than he at that time. With great enthusiasm I read the book and that's when I found a light at the end of the tunnel. An engineering path that led me to destinations that really motivated me and where I could enjoy applying what I have learned during my studies. And this was the bio-construction (also known as eco-construction, green building, etc.). I didn’t have in mind any particular type of bioconstruction, just a general idea of sustainable construction, recyclable materials, etc. I knew this was what I had to search for the topic of my project. And finally, thanks to the list of teachers that Dr. Nowak gave me, I contacted Professor Piotr Narloch, who introduced me in the fascinating world of rammed earth. He gladly accepted to be my tutor in the project and invited me to collaborate with student groups that were carrying out interesting research in the laboratories of the university with this material. Finally, to realize the theme of my project, I had to find a tutor at the Polytechnic University of Valencia and thank Professor Ignacio Payá I came to Professor Maria Teresa Pellicer, who had worked in several restoration projects with rammed earth buildings in Valencia. She agreed to be my PFC tutor in the UPV and

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gave me several bibliographical references of interest. It’s important to note the book "Arquitecturas de Tapia" by F. Font and P. Hidalgo, who was my coffee table book practically all Erasmus. So, I finally found my engineering vocation, an area in engineering with a great future and that gives me great personal satisfaction on helping either other people and the environment, with the experience gained in the Valencia School of Civil Engineering and in the Warsaw School of Civil Engineering (Wydziału Inżynierii Lądowej).

1.2. OBJECTIVES The main objective of this paper is to analyse how is the procedure in simple compression tests on specimens of rammed earth in laboratories around the world. This analysis is intended to serve as a basis for discussion of the best technique to proceed with this type of test that is one of the most important ones for building with any material. This work will help the creation of standards for the technique of rammed earth in Poland that is being developed at the University Politechnika Warszawska under the supervision of Professor Piotr Narloch. As secondary objectives, this document aims to raise awareness to any interested reader about the possibilities of this construction technique, the possible lines of research and the need to continue working and improving this building technique. It also aims to raise awareness of the need for change in the production model that prevails in our world, both in the field of construction and in the field of energy and agriculture, leading each of these points towards absolute sustainability in harmony with the planet on which we live.

1.3. WORK SCHEDULE This project has been written during the academic year 2014-2015. From October to December (2014): Finding information and reading about sustainable construction in general, focusing on rammed earth at the end. Selection of the information and start writing the state of art. From January to April (2015): Reading articles about simple compressive strength on rammed earth. Selection of the best articles, which either contain more information about the test or have interesting conclusions. Start making tables about the simple compressive strength tests. May (2015): Simple compressive test at the University Politechnika Warszawska with Mr. Narloch’s students group. Analysis of results and writing about the experience. June (2015): Writing conclusions about the analysed tests. Sum up of the thesis and format set of the whole document. There have been a lot of translation work continuously, from Polish to English or from Spanish to English. Finally, the work has been redacted in English but it is going to be translated totally to Spanish during the summer, and possibly adding a practical section on the design of a rammed earth wall.

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2. STATE OF ART: EARTH AS A BUILDING MATERIAL 2.1. EARTH BUILDING TECHNIQUES In this chapter we explain the most famous earth building techniques around the world. In addition, there is a short explanation of each one. Next to this, we will discuss why we have chosen Rammed Earth between all of them. In the Fig. 1 we can see a chart with the different techniques, classified in three big groups: brickwork, structure and monolithic. In the last one we can find the rammed earth technique.

FIG. 1 EARTH BUILDING TECHNIQUES CHART [5]

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2.1.1. BRICKWORK 2.1.1.1. Pressed bloks or compressed earth The soil, raw or stabilized, is slightly moistened, poured into a steel press (with or without stabilizer) and then compressed either with a manual or motorized press. It is a development from traditional rammed earth. It seems that the first attempts at Compressed Earth Blocks (CEB) were tried in France, in the first years of the 19th century: the architect Mr. Francois Cointreaux tried around 1803 to pre-cast small blocks of rammed earth. He used hand rammers to compress humid soil into small wooden moulds which were held with the feet. One had to wait till 1950 in Colombia for a housing research programme to improve the hand-moulded adobe. The result of this research and development (R&D) was the Cinvaram, the ancestor of the steel manual presses, which could make very regular blocks in shape and size, denser, stronger and more water resistant than the common adobe. CEB technology has been a great mean for the worldwide renaissance and promotion of earth construction in the 20th century.

FIG. 2 CINVARAM - THE FIRST PRESS FOR COMPRESSED EARTH BLOCKS [5]

2.1.1.2. Tamped blocks Hand-operated presses have been used for many decades. Before that, and still today, some people make the blocks by beating soil into a wooden mold with a stick. "Rammed earth" is a similar process, in which case a structure is made as one continuous mass of compressed earth.

2.1.1.3. Bloques de tierra cortada (cut blocks) In areas where the soils was cohesive and contained concretions of carbonates (a natural chemical which give cohesion) the soil was cut in the shape of blocks and used like bricks or stones. Such examples are found typically in tropical areas where lateritic soils give a wonderful building material. Lateritic soils can be found in two natural states: 



Soft soils, which will harden when exposed to air due to chemical reaction of the soil constituent with the air (carbonation reaction). This natural reaction is called induration. Such soils can be found on the west coast of India, from Kerala to Goa. Hard crust which was long ago a soil and has already hardened (indured) through the ages. Burkina Faso in Africa and Orissa in India show wonderful examples of such soils and blocks.

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Since a while the name laterite has been replaced by two more specific names: plinthite instead of laterite soft soil and petroplinthite for the hard crust laterite.

FIG. 3 BURKINA FASO, QUARRY OF KARI KARI [6]

2.1.1.4. Turf (or sod) houses In areas where the soil is not cohesive enough, people have used topsoil and grass to create blocks which were stacked fresh upon each other. This method has been used a lot in England, where it has been named sod. In the early days of the United States of America, in South America as well as long ago in Scandinavia, sod blocks cut out of topsoil were extensively used. In Uruguay one can still see quite a few beautiful examples of sod buildings.

FIG. 4 SOD HOUSE IN MINESSOTA, EEUU [5]

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2.1.1.5. Extruded earth The earth extrusion technique has been used since a long while in the fired brick industry. Stabilised earth, at a plastic state, is as well extruded through a machine which gives the desired shape. The blocks are often hollow and are cut to the desired length. This technique of stabilised extruded earth was developed in the 20thcentury. Compared to the brick extrusion in the fired brick industry, stabilised extruded earth bricks show a major inconvenient: the soil required for stabilised earth is much sandier than the one for fired earth. Thus the soil is more abrasive and the machines get damaged at a much faster rate.

FIG. 5 EXTRUDED EARTH MACHINE IN FRANCE [5]

2.1.1.6. Hand and machine moulded adobe Sun dried clay brick, named Adobe, is undoubtedly one of the oldest building materials used by mankind: The oldest identified adobes were produced around 9.000 BC at Dja’ De El Mughara in Syria. Adobes are made of thick malleable mud, often added with straw. After being cast they are left to dry under sun. They are traditionally either hand shaped or shaped in parallelepiped wooden moulds. The name adobe comes from the Egyptian hieroglyph dbt, meaning brick. It has passed via Coptic τωωβε in Arabic, as Al-ţŭb. When Arabs invaded Spain and France, the word has been deformed progressively as A Thob, A Dob and it became finally adobe in French and in English. This technique has been used all over the world since memorial times, as can been seen on various hieroglyphs and Egyptian scriptures. The oldest samples known were found on the site of Jericho, in the Jordan Valley, in Mesopotamia. They date from around 8000 BC and they were hand shaped. They looked like an elongated loaf. Fingerprints of the craftsmen who did them are still visible on some of them. In Peru the hand shaped adobes were long ago conical. In the Middle East they were at a time hemispherical and humpbacked. In India the archaeological site of Chitradurga in Karnataka state shows also hand shaped adobe of the 15th century. They were like quadrangular loafs. Today one can still find hand shaped bricks in Africa, in countries like Nigeria or Niger where they are called Tubali. Adobe production has been industrialised in Western USA (See Fig. 8). Several states in USA have codified adobe making and construction. [5]

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FIG. 6 EGYPT, THEBES, TOMB OF REKHMIRE - 15TH CENTURY BC - ADOBE MAKING (DRAWING OF THE ENTIRE FRESCO) [5]

FIG. 7 HAND MOULDED ADOBE IN LADAKH, INDIA [5]

FIG. 8 INDUSTRALIZATION OF ADOBE PRODUCTION [5]

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2.1.2. STRUCTURE 2.1.2.1. Earth sheltered space (or covered earth) Soil has been traditionally used to cover roofs in different parts of the world. In arid climates, either very hot or very cold, it regulates the inside temperature, due to heavy thermal mass. In Scandinavia, the earth to cover roofs was taken with grass, so as to hold the soil and give cohesion to it through their roots. This method gave also more thermal mass and allowed the inside temperature to be more even. In Nordic countries but also in the Himalayas regions, waterproofing was done long ago with the bark of birch trees. The bark peeled from the tree was very thin and it was applied in several layers to get a waterproof effect. Nowadays, waterproofing is done with PVC or bitumen sheets. Green roofs are today a modern development of the technique of covered earth. Green roofs, also known as vegetated roof covers or eco-roofs are multi-beneficial structural components that help to mitigate the effects of urbanization on water quality by filtering, absorbing or detaining rainfall.

FIG. 9 EARTH SHELTERED SPACE IN SÆNAUTASEL, ICELAND [7]

FIG. 10 HOUSE WITH GREEN ROOF IN NORWAY [7]

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2.1.2.2. Fill-in Humid soil was traditionally poured into wooden lattice works. Thus, it gave some thermal mass to light structures as well as some acoustic insulation. In recent times, dry soil has been poured into synthetic textiles which are hold outside by wooden poles driven into the ground. Dry soil is also being poured into long synthetic tubes, which are staked upon each other. Cal-Earth (The California Institute of Earth Art and Architecture) www.calearth.org which was founded and headed by the architect Nader Khalili does an extensive use of filled in technique. They call it Superadobe construction and they are building what is called Eco-domes. Superadobe structures are an excellent example of green building techniques. They use Tubular roll of sandbag-type material which are filled with earth. A barbed wire is use to bind the earth tube together. Later on the earth tubes are plastered with stabilised earth plaster. [5]

FIG. 11 ECO-DOME IN CONSTRUCTION [5]

FIG. 12 EARTH ONE IN THE SNOW [5]

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2.1.2.3. Straw clay or formed earth Very clayey soil, in a liquid state, is poured on straw, which has been chopped to the desired length. The mix is generally tampered afterwards into forms. These walls are not load-bearing: they are light, have a very high thermal insulation value and must be built in a wooden structure. It was traditionally used in Germany and was re-used for reconstruction after the 2nd world war. It is mostly known with the name Straw clay. Straw clay can be used as a filler wall, formed between a wooden structure or as prefabricated blocks.

FIG. 13 IN ORDER OF APPEARENCE: STRAW CLAY CONSTRUCTION IN BELGIUM, STRAW CLAY HOUSE IN GERMANY AND CLOSE STRAW CLAY PHOTO [5]

2.1.2.4. Cob on posts A mix of clay and straw is traditionally put between a wooden structures. Horizontally we have thin branches but vertically we have important load-bearing trunks. They are typically used for non-load-bearing partitioning interior walls. Thin clay panels are usually up to 30 mm thick and of a similar size to conventional plasterboard panels. [8]

2.1.2.5. Wattle and daub Wattle and daub is a composite building material used for making walls, in which a woven lattice of wooden strips called wattle is daubed with a sticky material usually made of some combination of wet soil, clay, sand, animal dung and straw. Wattle and daub has been used for at least 6000 years and is still an important construction material in many parts of the world. Many historic buildings include wattle and daub construction, and the technique is becoming popular again in more developed areas as a low-impact sustainable building technique. Generally, these structures are found as internal partition walls, which are not directly exposed to the climatic conditions. [12]

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FIG. 14 NON-STRUCTURAL DAUBED EARTH WALL IN A STORE STRUCTURE, CALATAÑAZOR, SORIA, CASTILLA Y LEÓN. (PHOTO: VALENTINA CRISTINI WITH JOSÉ RAMÓN RUIZ CHECA) [9]

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2.1.3. MONOLITHIC 2.1.3.1. Dug out The earth is dug out to create shelters. In most of cases dwellings are dug out in soft soils, tuffs, loess or porous lava in areas with hot and dry climate. Depending on the morphology of the site, the earth is either dug in depth or on a hillside. The horizontal dug out create caves on the side of the hills, which are accessed by staircases and galleries, such as in China for the school of Fenghuo in the Xiang region. The vertical dug out are created in areas such as plateaus or plains. A kind of open courtyard is dug out a few meters deep and then room are dug out like caves on the side of this courtyard. Access to the dwelling is done by a staircase, often very steep. Beautiful examples are found in China, in the provinces of Hunnan, Shanxi, and Gansu, where more than 10 million people live in homes dug out of the loess layer. In Tunisia too, one can find interesting achievements. In Turkey, Cappadocia show exceptional creations where people combined vertical and horizontal dug out. [5]

FIG. 15 SCHOOL OF FENGHUO, REGION OF XIANG, CHINA (PHOTO BY J.P. LOUBES) [5]

FIG. 16 CAVE ROOM, CHINA [5]

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2.1.3.2. Poured earth The soil, in a liquid state, is poured like concrete into formworks. The soil characteristics must be very sandy or gravely and should be stabilised. This technique is a new development and is very seldom used. The reason is that the high water content of the soil will induce a lot of shrinkage when it will dry. Thus the wall will crack and generally a lot.

FIG. 17 NEW ZEALAND (PHOTO BY MILLES ALLEN) [5]

2.1.3.3. Cob Plastic soil is usually formed in balls, which are freshly stacked upon each other. This technique has been used a lot long ago in Europe, where it was named cob in England and bauge in France. This technique is still used a lot in Africa, India and in Saudi Arabia, where beautiful examples can be seen. The most beautiful examples are encountered in Yemen with Shibam. This old historic capital of Southern Yemen has been named “The Manhattan of the Desert”. Shibam was recorded by UNESCO as a world heritage site. In fact Shibam was built with a combination of cob and with adobe. Since a while, cob is getting known again with some development in USA, as well as in other parts of the world. We show hereafter only worldwide traditional developments.

FIG. 18 SOUTHERN YEMEN, SHIBAM (PHOTO PATRICK MEYER) [5]

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FIG. 19 BURKINA FASO [5]

FIG. 20 SHIBAM CITY AND DESERT [5]

FIG. 21 TWO STOREYS COB HOUSE IN FRANCE [10]

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FIG. 22 COB FURNITURE AND STOVE [11]

FIG. 23 SHAPED EARTH IN CAMERUN (PHOTO BY GERT CHESI) [5]

2.1.3.4. Rammed Earth 2.1.3.4.1. Traditional Rammed earth, also known in French as pisé de terre or simply pisé has been used since ages worldwide like many other earth techniques. The earth is mixed thoroughly with water to get a homogeneous humid mix. This humid earth is poured in a form in thin layers and then rammed to increase its density. The increase of density increases as well the compressive strength and the water resistance. Ramming was traditionally done by hand. Since a few decades, ramming is being done mechanically with pneumatic rammers (see modern rammed earth). The worldwide tradition of rammed earth construction has shown that it is possible to achieve long lasting and majestic buildings from single to multi storey. Wonderful heritage can be found in countries such as France, Spain, Morocco, China, and all over the Himalayan area. One can see numerous and wonderful examples with all kinds of buildings:   

Farms, or rural houses, chateaux and apartments in Europe Entire villages in North Africa Parts of the great wall of China

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 

Buildings in most of the Himalayan regions of Tibet, Bhutan, Nepal, Ladakh Widespread examples in South America

Soil identification Like any other earth building technique, one should select the best soil, according to the requirements. Knowing that the best soil for rammed earth is preferably sandy or gravely rather than clayey, one should take a lot of care about the clay content. Worldwide, the skill and knowledge of people has led them to choose rammed earth when the soil was more sandy or gravely. When the local soil was more silty or clayey they chose other techniques like Adobe, Cob or Wattle and Daub. Preparation After being excavated, the soil is thoroughly sieved, to break the lumps and make it lighter. Big rocks should be removed but some stones could be kept. If the natural soil is too dry, it should moistened and mixed so as to get a uniform humid mix. Formwork types Two techniques have traditionally been developed. They used either horizontal or vertical formworks. The horizontal technique was used in many parts of the world. Strips of walls were built horizontally and their height varied from 30 to 90 cm. The formwork consisted of 2 wooden panels held together with wooden clamps and keys, which were tightened with ropes. Once one portion of a wall was completed, the formwork was immediately dismantled and moved further along the side of the wall, as showed here in Morocco or China.

FIG. 24 HORIZONTAL FORMWORK FOR RAMMED EARTH FROM MOROCCO

FIG. 25 HORIZONTAL FORMWORK FOR RAMMED EARTH FROM CHINA

FIG. 26 VALENCIAN RAMMED EARTH (LEFT) AND CALICOSTRADA (RIGHT) [1]

16

FIG. 27 TRADITIONAL FORMWORK FOR RAMMED EARTH [1]

The vertical technique was used in a few places in the world: mainly in Tibet, China and one region of France (Bugey). The walls were built vertically to their full height at once. Long poles were anchored in the ground to hold side panels, which were made of wood and tightened with rope. The entire height of the wall was built course after course. Once a course was completed, the side panel was raised to ram a next course and the process went on till the entire height of the wall was completed.

FIG. 28 VERTICAL FORMWORK FOR RAMED EARTH IN CHINA [5]

Humid soil was evenly poured into the formwork to get a regular course of about 12-15 cm thickness. The soil is first rammed along the sides of the panels and the central portion of the wall is rammed immediately after that. Every course is rammed till the rammer hitting the soil gives a clear sharp sound and the rammer is not doing anymore marks on the course.

17

Once a course has been completed, the process goes on in the same way for the following courses till the maximum height of the panels. Immediately after completion, the formwork is removed and shifted either sideways in the case of the horizontal technique or lifted up for the vertical technique.

FIG. 29 SPAIN - CASTILLO DE BIAR, 12TH CENTURY (PHOTO PAUL JAQUIN) [5]

FIG. 30 TIBET, LHASA - POTALA PALACE [5]

FIG. 31 FRANCE, SAINT SIMÉON DE BRESSIEUX - LONGEST BUILDING IN EUROPE [5]

2.1.3.4.2. Modern Soil stabilization gave a great input to rammed earth as well as mechanization. The traditional wooden rammer has been replaced by pneumatic rammers. Heavy wooden formworks evolved into light composite ones, made of plywood, wood and steel or sometimes aluminium. Pneumatic rammers, dumpy loaders, mixers, ban conveyors, etc. allowed to build faster and get a better quality finish. Structures are most of the time built with pier walls, meaning that walls are built up to their full height at once. This way of building changed totally the design pattern of structures. Australia and Western USA have seen the widest development. David Easton in California http://www.rammedearthworks.com does wonderful works. More and more development happens also in Canada, and other countries of Europe such as UK with “Earth structure Europe” http://www.earthstructures.co.uk and Austria with Martin Rauch http://www.lehmtonerde.at. Since a few years stabilised rammed earth is being more and more used, furthermore new standards are being created. [5]

FIG. 32 MIX SUPPLY, PNEUMATIC RAMMING AND VERTICAL FORM (IN ORDER OF APPEARANCE) [5]

18

FIG. 33 KOREA - HOUSE AT SANCHON BY SHIN GEUN SHIK [5]

FIG. 34 AUSTRIA, PIELACH – OFFICES BY MARTIN RAUCH [5]

19

FIG. 35 AUSTRALIA – KOORALBYN RESORT BY DAVID OLIVER [5]

20

2.2. EARTH BUILDINGS AROUND THE WORLD We could have added thousands of examples of earth buildings around the world. Here is a small summary of houses in different countries with different climates as a proof that building with earth is not only a building technique for poor regions. It is known that building with earth gives to the big cities a relaxing point of beauty and touch with nature, which are more necessarily than grey spots provided by concrete structures and fumes. However, earth buildings use to be in separate zones because they cannot compete in height with tall buildings made of concrete and steel. Despite of that, there is no reason for not including earth buildings in city centres, turning them into a sustainable construction reference for the rest of the world. Instead of pretending to touch the sky with their buildings, this is a way to be more respectful of the environment and the resources that this planet has given to us.

21

2

Church of Sant Agustí de Castelló

Nº

NAME

1

Municipal swimming pool

FUNCTION

EARTH BUILDING TECHNIQUE

Public

Modern Rammed Earth

Yes

Public (auditorium and museum)

Valencian Rammed Earth

Yes

2

CLIMATE ZONE

Mediterranean

Mediterranean

STOREYS

ADDITIVES

OTHER INTERESTING INFORMATION

3

White cement and aerial lime

CITY (COUNTRY) Zamora (Spain)

Vinaròs (Spain)

LOAD-BEARING EARTH

DATE

FIG. 37 [1]

2010

FIG. 36 [1]

s. XII

PHOTO

Organic base siloxanes product is applied on the walls for protection

22

FIG. 41 [13]

The vaults are plastered with an earth plaster, which is covered by an elastic acrylic waterproof paint

1 No

The half upper part of the tower was rebuilt by Christians with stone masonry

The exterior surfaces are covered with straw-loam plastering

2

1

25 m

No

Yes Yes Yes

Handmade adobes Earth-filled rammed sacks Rammed Earth

No

Residence Country house Public and Commercial Building

Hot Mediterranean climate

National wine center

FIG. 40 [12]

6

Tabiya (muslim Rammed Earth)

Highlands Semiarid

Military

Villena (Spain) La Paz (Bolivia) Moab, Utah (USA) Adelaide (Australia)

5

Honey House

FIG. 39 [12]

Semiarid

s. XII-XV 1999

4

1998

FIG. 38 [1]

2002

Castillo de la Atalaya

3

The metal structure is embedded into the earth walls, and these walls work as bracing the resistant structure

23

5 Well-lit, well-ventilated, wind-proof, earthquake-proof, warm in winter and cold in summer

2

Stone, bamboo, wood or other readily available materials

Rammed Earth

Straw clay cubes with wooden structure

Straw

Residence

Residence

Yes

Semitropical

Humid Continental

No

Fujian (China)

FIG. 43 [12]

Turku (Finland)

8

s. XIII-XX

FIG. 42 [14]

1999

Toulous

7

The blocks are covered either by timber planks or lime plaster

24

10

Casita Nuanarpoq

Residence and studio

Residence

Residence and office

2

2

Yes

Autonomous in energy terms

2

Cowdung

Yes

Sun-dried, unstabilised and locally made adobes

Highlands

Desert

Semiarid

Handmade adobes at the lower storey and post-andbeam timber structure with adobe infill

Gallina Canyion (New Mexico)

Taos (New Mexico)

FIG. 46 [12]

Bowen Mountain (Australia)

11

2001

FIG. 45 [12]

2004

FIG. 44 [12]

2004

9 It displays several features of environment-conscious design: solar heating, thermal chimney, photovoltaic system and water harvesting system

Walls are plastered on both sides with mud plaster. The exterior plaster is stabilized with cow dung

25

Nursery

Mediterranean

1

No

Yes

CEB (compressed earth blocks)

FIG. 47 [15]

Barcelona (Spain)

2010

Santa Eulàlia de Ronçana school

12 There is also a curved rammed earth wall

TABLE 1 EARTH BUILDINGS AROUND THE WORLD

26

2.3. RAMMED EARTH STANDARDS 2.3.1. DEFINITIONS With regard to their scope of application, the documents can be classified into three types, each dealing with a particular aspect:  Soil classification  Earth building materials  Earth construction systems Our analysis shows that standard internationally accepted terminology is still lacking. This, however, is an essential general prerequisite for developing standards and normative documents. [8] The International Standards Organisation (ISO) [16] distinguishes between the terms standards and normative documents as follows: 

A standard is a ‘document, established by consensus and approved by a recognised body, that provides, for common and repeated use, rules, guidelines or characteristics of activities or their results, aimed at the achievement of the optimum degree of order in a given context’ and ‘should be based on the consolidated results of science, technology and experience, and aimed at the promotion of optimum community benefits’.



A normative document is a ‘document that provides rules, guidelines and characteristics for activities or their results’, and as a result has neither the scope nor the endorsement of a standard, although it can become a ‘standard’ after adoption by a governmental body. Normative documents are developed by a group of specialists or organisations with proven competence in the respective field and are published for general use. Technical standards, including those for building, can also be classified into different groups according to the geographic area and corresponding issuing organisation.

Technical standards, including those for building, can also be classified into different groups according to the geographic area and corresponding issuing organisation:  International standards These are issued by the International Organisation for Standardization (ISO) in Geneva with about 150 members represented by the national organisations for standardisation.  Regional standards These are issued in Europe by the European Committee for Standardization (CEN) in Geneva as European Standards EN. Members of the CEN are all member states of the EU as well as Switzerland and Norway. In addition, there are also European Building Codes (‘Eurocodes EC’) that describe uniform standards for the design, measurement and construction of buildings in the EU, e.g. the ‘measurement and construction of brickwork’ (EC 6). Earth blocks do not feature in this building code.

27

 National standards These are issued by the National Standards Bodies (NSB), in Germany the Deutsches Institut für Normung e.V. (DIN), which in turn are members of the CEN or ISO. National standards can also be issued by special (building) organisations or associations acting on a national level if they follow a predefined process of approval to acquire ‘legal status’. 

Local standards In the USA several regional standards bodies exist that are responsible for issuing local building codes for a specific federal state, county or even a city. [8]

2.3.2. HISTORY OF BUILDING CODES Earth is one of the oldest building materials known to mankind. According to archaeological excavations, the first use of earth as a building material dates back to the Neolithic period in approximately 10 000 BC in the warm and dry climate of the eastern Mediterranean and Mesopotamia in what is today Anatolia (Turkey), Syria, Jordan, Lebanon, Israel (Palestine) and Iraq. Rammed earth foundations dating from 5000 BC have been discovered in Assyria. [12] For thousands of years earth was the prevailing building material for house construction in many regions of the world with appropriate soils and climatic conditions. As a result, it became necessary to develop rules for using this material for building purposes. Written or painted documents describing earth building served as early ‘rules’ for using earth as a building material. Fig. 1 depicts the process of building with mud blocks in ancient Egypt. There are also pictures which show quite some detail including the block sizes, the block bonds in the wall construction and the use of a plumb as an expression of the technical standards and quality control mechanisms of masonry work at the time. [8]

FIG. 48 BUILDING WITH MUD BLOCKS IN ANCIENT EGYPT [17]

28

In Central Europe the history of technical rules in the field of earth building is closely related to the development of cities in the 14th and 15th centuries. As a result of their rapid growth, the availability of timber as primary building material became scarce. Moreover, timber structures were susceptible to fire damage, and fires were responsible for wiping out entire portions of cities, either by accident or as a result of war. Both problems led to the drawing up of the first mandatory building codes across several German states. The Ernestine Building Code, introduced in 1556 in the state of Thuringia, did not permit houses to be solely constructed of timber but only as timber frame structures in combination with fired bricks, adobe or natural stone, or alternatively as Weller-structures, the German variant of cob. The Saxony Forester Code drawn up in 1575 permitted the use of timber for new house constructions only when the first floor could not be built of stone or cob. Two hundred years later, other building codes for Saxony (1786), Prussia (1764) and Austria (1753) (called ‘Egyptian stones’) for wall construction. For hundreds of years building codes enforced the use of earth for building purposes by restricting the use of timber for house constructions. [8]

In France, the rammed earth technique, called terre pisé, was widespread from the 15th to the 19th centuries. Near the city of Lyon, there are several buildings that are more than 300 years old and are still inhabited. The technique came to be known all over Germany and in neighbouring countries. In Germany, the oldest inhabited house with rammed earth walls dates from 1795. Its owner, the director of the fire department, claimed that fire-resistant houses could be built more economically using this technique, as opposed to the usual timber frame houses with earth infill. The tallest house with solid earth walls in Europe is at Weilburg (Fig. 49), Germany. Completed in 1828, it still stands. All ceilings and the entire roof structure rest on the solid rammed earth walls that are 75 cm thick at the bottom and 40 cm thick at the top floor (the compressive force at the bottom of the walls reaches 7.5 kg/cm2. [12]

29

FIG. 49 TALLEST EARTH BUILDING IN EUROPE AT WEILBURG (GERMANY) [18]

The use of earth was characterized by a high degree of manual work. After around 1850, the industrial revolution brought about a fundamental change in the way building materials were produced in many industrialized countries: the mechanization of production processes meant that building materials such as fired bricks could now be produced in large factories more economically and at better quality than before. Nevertheless, from the end of the 19th century new building materials such as steel, cement, concrete and reinforced concrete began to displace the use of earth until it was only rarely used.

In Germany, earth experienced a brief revival after each of the world wars. As a consequence of industrialization, building standards or regulations for building with earth were developed in just a few countries. The German Earth Building Code (the Lehmbauordnung), drawn up in 1944, was the first contemporary technical standard in Europe dedicated to earth as a building material. The code summarized the entire technical knowledge of building with earth available at the time. In 1944, a year before the end of the Second World War, the industrial basis had been destroyed along with vast numbers of houses: millions of people were homeless and urgently needed new shelter. Very often earth was the only locally available building material.

30

The German State Building Authority’s intention was to regulate the use of earth as a building material for the period of reconstruction after the war. However, as a result of post-war reorganization, the code could only be put into effect seven years later in 1951 as DIN 18951. In the five years that followed its issue, a number of further DIN-codes were drafted, dedicated to different fields of building with earth. Of these only the first, DIN 18951, came into force – all the others did not progress beyond draft status.

By the 1970s, the use of earth as a building material had all but disappeared as a result of industrialization, and in 1971 the DIN was withdrawn and not replaced.

At the beginning of the 1980s, after the experience of the oil crisis in 1973 and health scandals caused by so-called modern building materials, a new way of thinking arose in some industrialized European countries: alongside ‘traditional’ economic and technical aspects such as durability, strength and so on, consumers started to give greater consideration to ecological aspects such as health, recyclability and low embodied energy as well as aesthetic and ‘soft’ design factors such as indoor climate, colour and surface qualities.

These ‘new’ ecological aspects are now anchored in the European Union framework of building regulations. The principle of ‘life cycle assessment LCA’ as a method for evaluating the sustainability of building materials will lead to a new generation of building standards. LCA is an objective process to evaluate the environmental loads associated to a product, process or activity by identifying and quantifying the use of mass and energy and the discharges to the environment. LCA accounts for all energy inputs and outputs of a building during its entire life cycle, including manufacturing, use, and demolition phases. [8]

FIG. 50 IMPACT POINTS OF THE MANUFACTURING PHASE IN A LCA METHOD [19]

31

The process of quantifying the resource use and environmental releases of products became known as a Resource and Environmental Profile Analysis (REPA), as practiced in the United States. In Europe, it was called an Eco-balance. With the formation of public interest groups encouraging industry to ensure the accuracy of information in the public domain, and with the oil shortages in the early 1970’s, approximately 15 REPAs were performed between 1970 and 1975. Through this period, a protocol or standard research methodology for conducting these studies was developed. This multistep methodology involves a number of assumptions. During these years, the assumptions and techniques used underwent considerable review by EPA and major industry representatives, with the result that reasonable methodologies were evolved.

In 1991, concerns over the inappropriate use of LCAs to make broad marketing claims made by product manufacturers resulted in a statement issued by eleven State Attorneys General in the USA denouncing the use of LCA results to promote products until uniform methods for conducting such assessments are developed and a consensus reached on how this type of environmental comparison can be advertised non-deceptively. This action, along with pressure from other environmental organizations to standardize LCA methodology, led to the development of the LCA standards in the International Standards Organization (ISO) 14000 series (1997 through 2002).

In 2002, the United Nations Environment Programme (UNEP) joined forces with the Society of Environmental Toxicology and Chemistry (SETAC) to launch the Life Cycle Initiative, an international partnership. The three programs of the Initiative aim at putting life cycle thinking into practice and at improving the supporting tools through better data and indicators. The Life Cycle Management (LCM) program creates awareness and improves skills of decision-makers by producing information materials, establishing forums for sharing best practice, and carrying out training programs in all parts of the world. [20]

32

FIG. 51 LIFEC CYCLE STAGES [20]

In the context of these developments, earth as a building material can be seen in a new light.

33

2.3.3. OVERVIEW OF EXISTING EARTH BUILDING STANDARDS AND NORMATIVE DOCUMENTS Thirty-three different documents have been identified from 19 countries published by regional, national or local standards bodies over the last 30 years. This fact demonstrates that earth building techniques are being more and more studied due to its good qualities, either in sustainability, health properties or structurally.

TYPE OF DOCUMENT:  S: STANDARDS ISSUED BY THE NATIONAL STANDARDS BODIES (NSB)





OR SPECIALIZED ORGANIZATIONS THAT HAVE PASSED A PREDEFINED PROCEDURE OF APPROVAL AND ARE RECOGNIZED BY A STATE BUILDING AUTHORITY. BC: BUILDING CODES ISSUED BY NSBS WITH ONE OR MORE CHAPTERS ON BUILDING WITH EARTH. ND: NORMATIVE DOCUMENT ISSUED BY SPECIALISED ORGANIZATIONS THAT HAVE PASSED A PREDEFINED PROCEDURE OF APPROVAL BUT ARE NOT

SOIL:  E: EARTH  ES: EARTH STABILIZED WITH CEMENT GEOGRAPHICAL LEVEL:  L: LOCAL  N: NATIONAL  R: REGIONAL

MATERIAL AND/OR BUILDING TECHNIQUE:  EB: EARTH BLOCK, ADOBE  CEB: COMPRESSED EARTH BLOCK  CSEB: COMPRESSED STABILIZED EARTH                

BLOCK PEB: POURED EARTH BLOCKS EM: EARTH MORTAR EP: EARTH PLASTER EMM: EARTH MASONRY MORTAR ESM: EARTH SPRAY MORTAR LE: LIGHT EARTH EP: EARTH PLASTER C: COB LC: LIGHT CLAY CP: CLAY PANNEL EI: EARTH INFILL WD: WATTLE AND DAUB PEI: POURED EARTH INFILL RE: RAMMED EARTH CSRE: CEMENT STABILIZED RAMMED EARTH EBM: EARTH BLOCK MASONRY

34

2.3.4. STANDARDS ABOUT BUILDING WITH EARTH AROUND THE WORLD Soil

Building materials

Building technique

Geographica l level

EB

EBM

R

C, LC, EB, EM, CP

RE, C, EBM, EP, EI, WL

N

Nº

Country

Name of the document

Type

1

Africa

ARS 671-683 (1996)

S

2

Germany

Lehmbau Regeln (2009)

S

3

Germany

RL 0803 (2004)

ND

EP

N

4

Germany

TM 01 (2008)

ND

EP

N

5

Germany

TM 02 (2011)

D

EB

N

6

Germany

TM 03 (2011)

D

EMM

N

7

Germany

TM 04 (2011)

D

EP

8

Germany

TM 05 (2011)

ND

E

9

Australia

CSIRO Bulletin 5, 4th ed.1995

ND

E

EB, CSEB, EMM

RE, EBM

N

10

Australia

EBAA (2004)

ND

E

EB, EMM

EBM, RE

N

11

Brasil

NBR 8491-2, 10832-6, 12023-5, S 13554-5 (1984-96)

12

Brasil

NBR 13553 (1996)

S

13

Colombia

NTC 5324 (2004)

S

E

RE

N N

CSEB

N CSRE

CSEB

N N

35

14

EEUU

UBC, Sec. 2405 (1982)

BC

15

EEUU

14.7.4 NMAC (2006)

BC

16

EEUU

ASTM E2392/E2392M (2010)

S

E

17

Spain

MOPT Tapial (1992)

ND

E

18

Spain

UNE 41410 (2008)

S

CEB

N

19

France

AFNOR XP.P13-901 (2001)

S

EB

N

20

India

IS: 2110 (1998)

S

21

India

IS: 13827 (1998)

S

EB

22

India

IS: 1725 (2011)

D

CSEB

N

23

Kenya

KS02-1070 (1999)

S

CSEB

N

24

Kyrgystan

PCH-2-87 (1988)

S

25

Nigeria

NIS 369 (1997)

S

26

Nigeria

NBC 10.23 (2006)

BC

27

New Zealand NZS 4297-9, (1998)

S

28

Peru

S

NTE E.080 (2000)

EBM

L

EB, EMM

EBM, RE

L

EB, EMM

C, EBM, RE, EM, WL

N

RE

N

E, ES

E, ES

RE

N

EBM, RE

N

RE CSEB

E

N N

EBM, RE

N

E, EB

RE, EBM, EP

N

EB

EBM

N

36

29

Sri Lanka

Specification for CSEB, SLS 1382 S part 1-3 (2009)

30

Switzerland

Regeln zum Bauen mit Lehm ND (1994)

31

Tunisia

NT 21.33, 21.35 (1998)

S

CEB

N

32

Turkey

TS 537, 2514, 2515 (1985-97)

S

CSEB

N

33

Zimbabwe

SAZS 724 (2001)

S

E

E

CSEB

EBM

N

EB, LE, EM

EBM, RE, EI, WL

N

RE

N

TABLE 2 STANDARDS ABOUT BUILDING WITH EARTH AROUND THE WORLD. ADAPTED FROM [8] PP: 79-81

37

2.3.5. COMMENTS Through this table we can see that the most of the earth standards are not about rammed earth but earth blocks. And the ones which talk about rammed earth are not only focusing on this technique. Is shown in the table that there are six codes about rammed earth exclusively (7, 12, 17, 20, 24, 33). One of them is MOPT Tapial (1992) [21] from Spain yet it is too old and short (only 80 pages). With all the improvements that this technique has suffered during this last years, what we should have as a standard for rammed earth is a huge standard as we have for concrete or steel. We also can notice that this standards have been written in the last twenty years, what proves that this building technique is in constant development and increasingly used. Thus, is necessary to work in this direction as it is happening in the University Politechnika Warszawska, to stablish a Polish standard for rammed earth. On the other hand, the Universidad Politécnica de Valencia is not working with rammed earth at all, something incomprehensible for such a good university with one of the best laboratories in Europe for testing concrete: ICITECH (Instituto de Ciencia y Tecnología del Hormigón). Furthermore, to become useful in the building field, rammed earth requires standards which will have to take into account the complex hydro-mechanical behaviour of this material. This means Finite Element Models. Some models such as Boyce take into account an anisotropic elastic behaviour, and this will be the next improvement of the non-linear elastic model. Some additional models which take into account the plastic behavior under a large cycle number, e.g. the Suiker model, the Habibalah-Chazallon model and the François model. [22]

2.3.6. SPANISH CODES In Spain it is only in the mid-eighties of last century when it begins to revive interest in this humble material. In 1983 the engineer Julián Salas Serrano founded in Eduardo Torroja Institute, the research team "Technologies of very low cost housing." A year later the Technical Research Centre of Indigenous Materials of Navapalos (Soria), led by the architect Erhard Rohmer, where, since 1985 has taught numerous training courses in earth building, celebrating until 2006 working meetings in which participated the leading international experts in the field, soon becoming a reference and meeting place of European and Latin American professionals. One of the obstacles to boost unbaked earth construction is the lack of standards, because the truth is that in Spain, today, it is difficult to go beyond its use in the monuments or initiatives promoted by developers and architects bent on building with this material. [23] In 1992, the Ministry of Transportation and Public Works of Spain (Ministerio de Obras Públicas y Transportes) published a guidance document for the design and construction of earthen structures: MOPT Tapial (1992). The document has five main sections and the main focus is on rammed earth, although references and comparisons with adobe techniques are given.

38

The first section of the document is a general historical account of rammed earth and adobe. Section two details the design principles for earth walls, mainly for compression, tension and buckling. The third section examines the construction methods for rammed earth. The formwork used is detailed, the ramming methods demonstrated and the ideal construction sequence is explained. Finally, the construction of earth wall footings and corners is elaborated. The last section provides guidance on quality control measures in order to ensure compliance of the constructed earth walls with the design specifications. The guidance involves information on material testing, additives, reinforcement, formwork and general construction tolerances. [24] In 2008 the UNE standard on compressed earth blocks is born. Traditional techniques of adobe wall and traditional rammed earth joined in the fifties of the last century with the name of "Compressed Earth Block", known by the acronym CEB (BTC in Spanish). A piece of similar dimensions to the current brick, made by earth pressed and stabilized with cement, lime or plant fibres to improve thermal insulation, which is currently marketed in many European countries, even in Spain. We could also say that the Housing Ministry there appears to be interested in incorporating earth building to the current CTE (Código Técnico de la Edificación, which currently ignores earth construction, the material and the traditional techniques associated with it. In addition, there is coming a UNE standard about rammed earth. These initiatives can be undoubtedly a significant boost for earth construction and renovation. Hopefully soon materialized. [24]

39

3. DISCUSION ABOUT RAMMED EARTH AS THE BEST EARTH BUILDING TECNIQUE We hardly believe that there are not a best-choice building technique for all cases due to the techniques and materials have to be selected according to the historic and geographical context. However, when we owe the possibility for choosing between different techniques, there are several factors that invite us to use rammed earth as our first choice.

3.1. ENERGETIC COST AND ENVIRONMENTAL IMPACT First of all, rammed earth uses local material, earth from the same building excavation, which otherwise would be transported to an earth-dump. If the local material doesn’t fit for the purpose, other earth could be find near around always in aim to look for a usage of material that otherwise would be thrown to and earth dump. Thus, we don’t need too much concrete trucks in our roads, fact that helps to decrease the air pollution. Material Rammed earth (unstabilised) Adobe Mass concrete in situ Prefabricated concrete (2% steel) Massive brick wall Hollow brick wall

Density [Kg/m3] 2200 1200 2360 2500 1600 670

Emissions [Kg CO2/Kg] 0.004 0.06 0.14 0.18 0.19 0.14

Emissions [Kg CO2/m3] 9.7 74 320 455 301 95

TABLE 3 COMPARISON ABOUT DENSITY AND EMISSIONS OF SOME BUILDING MATERIALS [25]

Moreover, Portland cement production contributes to the emission of CO2 by burning fossil fuels and in the process of decarbonisation of limestone in the obtaining clinker. It produces approximately between 886 Kg and one tone of CO2 per ton of clinker, depending on production process adopted. That is, 13.5 billion tons annually, or, in other words, it is responsible for the emission of CO2 that varies between 5-8% of global emissions. [26] Despite the high costs of Portland cement, it is used improperly in many cases, particularly where low resistances are required, as in foundations, mortar coating and soil stabilization. Only 20% of the uses of cement are technically adequate [27]. This is why earth construction could be implemented as a co-working building technique in many concrete structures, decreasing economical cost and environmental impact.

40

3.2. PHYSICAL AND CHEMICAL PROPERTIES Furthermore, the physical and chemical properties of earth as a building material are marvellous. On the one hand, we can reach more than acceptable mechanic strength for five floors buildings (see Table 4), or even more with stabilized rammed earth. Material Adobe Cob CEB CEB stabilized bioterre Rammed earth unstabilised

Density [Kg/m3] 1200-1500 1615 1700-2000 1790 1900-2200

Compressive strength [MPa] 0.53-1.72 1 1-5 10.8 3-4

TABLE 4 SIMPLE COMPRESSIVE STRENGTH ACHIEVED BY SOME EARTH BUILDING TECHNIQUES [25]

In addition, besides their striking beauty and characteristic deep reveals, rammed earth walls have outstanding thermal and acoustic benefits. They have an ideal thermal transmittance (U-factor) and density or thermal storage (known as the "thermal flywheel" effect). This unique combination of properties creates a high thermal mass building, which evens out day/night temperature fluctuations and forms a comfortable building in which to live all year round. [28] Earth walls have good sound-absorbing characteristics and can be built to have very high sound attenuation (up to STC 57) which inhibits noise transfer between rooms extremely effectively. [28] Measurements taken in a new built house in Germany, all those interior and exterior walls are from earth, over a period of eight years, showed that the relative humidity in this house was nearly constant throughout the year. It fluctuated by only 5% to 10%, thereby producing healthy living condition with reduced humidity in summer and elevated humidity in winter. [12]

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Strawbale

Feature

Mud-brick

Timber frame

Double brick

Rammed Earth Wall (Ramtec)

Wall thickness

600mm

300mm

120mm

270mm

300mm

Impact strength

very low

moderate

very low

moderate

very high

Compressive strength

very low

moderate

moderate

high

high

Durability

vague

75–175 yrs.

50–100 yrs.

150 yrs+

250 yrs+

Fire resistance

moderate high

moderate

high

very high

Cyclone resistance

very low

moderate

moderate

high

very high

Tremor resistance

very low

moderate

moderate

moderate

high

Termite resistance

low

moderate

low

questionable

very high

Pest resistance

very low

moderate

very low

high

very high

Cavity problems

vague

none

yes

yes

none

Maintenance

vague

low

high

average

very low

Thermal insulation

very high moderate

moderate

moderate

moderate

Embodied energy

low

very low

low

extremely high

low

Thermal mass ability

poor

very good

poor

moderate

very good

Greenhouse gases & toxicity

good

good

good

very poor

good

Humidity equalisation

poor

excellent

very poor

poor

excellent

Bullet resistance

poor

good

very poor

good

very good

Natural harmony

moderate good

moderate

poor

good

Acoustic properties

moderate very good

poor

moderate

very good

Major lender-approved

vague

vague

reasonable

good

good

Approved by insurers

vague

yes

yes

yes

yes

All govt. depts. approved

vague

yes

yes

yes

yes

Cost to have built

1,15

1,2

0,9

1

1,05

Resale value

unclear

moderate

unclear

moderate

good

TABLE 5 COMPARISON OF ‘RAMTEC’ WITH OTHER COMPLETE WALL SYSTEMS AT 3 METER HEIGHTS [28]

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3.3. TEXTURES OF EARTH Other fact, according to the beauty of the construction, is that walls made of earth show an extraordinary variation in textures and colors, which is important not only for the appearance of the building, but also for integrate the buildings in the landscape, keeping the day-to-day life more in touch with nature. Also we avoid the necessity of paints that are toxic in most of cases.

TABLE 6 RAMMED EARTH & STABILIZED RAMMED EARTH WALLS [5]

The nice textures, the simplicity of the obtained surfaces and the wealth of tonalities that makes the ground possible seduce in a powerful way. These attractions come to explain why in most of earth constructions the proper material itself is visualized on the walls. Nevertheless, this option demands that the walls remain appropriately protected to minimize its erosion for the action of the rainwater, or, at least, that it is possible to control its degradation. In this sense M. Rauch suggests: "why not to make possible an erosion calculated with a process of controlled aging, like one more formal element?” [29], introducing a new approach with enormous possibilities to be explored. In Spain it has been experiencing on the application of water-repellent substances, different types of consolidation primers and surface treatments that help to satisfy the new demanded requirements. Water repellents, especially silicone resins, have been the most widely used products in the works carried out. The consolidation primers have been less used, but they will need experience in this field to improve the response of walls to erosion. When the factory must not be visible may extend a continuous coating, either a lime mortar or clay prepared. Another alternative is the calicostrada wall, but note that this solution, despite assurances of durability and a beautiful finish, does not enjoy the interest of architects because it requires very rudimentary and expensive manual methods. However, it is in this way as much of the old walls were built and therefore have to resort to this method in the monumental restoration. [23]

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FIG. 52 SIDE-VIEW OF A "CALICOSTRADA" RAMMED EARTH WALL (CASTELL VELL AT CASTELLÓN DE LA PLANA, SPAIN) [23]

44

3.4. RECYCLING EARTH AND EXTREME CLIMATES Earth is a sustainable material which can be used as many times as we want. The formwork used, can be used during a long period of time without changing it, so it is another advantage. The different earth building techniques are derived from local building traditions and are not always appropriate for use as contemporary technical terminology. Nevertheless, the existing building stock of traditional earth buildings must also be considered in standards concerning conservation work. And, if the restoration is not viable, we must know that earth is one of the most recyclable building materials, as it’s shown in Fig. 5.

FIG. 53 BUILDING WITH EARTH PRESENTED AS SELF-SUSTAINING LIFE CYCLE [30]

Rammed earth building offers the possibility of building or rebuilding with significantly increased resilience in the wake of the more frequent and devastating natural disasters that are occurring. For example, with the rebuilding of housing in New Orleans post-Katrina, the wisdom and validity of rebuilding in the same location with designs, methods and materials that did not withstand previous disasters should be questioned. Rebuilding with earth containing hydrophobic admixtures is a sustainable, healthy solution. There are frequent and destructive fires on the coast of California, the inland portions of Washington, Oregon, Idaho, Wyoming and the Canadian Okanogan. Small communities are repeatedly evacuated and consumed by fire with only the inorganic parts of the buildings such as chimneys and foundation walls remaining. When they rebuild, they rebuild with wood. Earth building is non-combustible. The big earthquake in Haiti left an abundance of rubble and thousands of people without homes and work. The chosen solution was to clear the rubble and dispose of it in order to build new buildings from imported materials.

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an opportunity missed was using modern rammed earth to create seismically resistant housing that is more comfortable and healthy using local labour and materials (rubble run through a concrete recycler), both of which were in abundance. Every year twisters touch down in Kansas hurling roofs and entire houses into the air. Every year in the southeastern US, people board up their houses and evacuate in fear of hurricanes. According to a local demolition specialist, mobile homes (trailer park houses) may weigh as little as a couple of tons, while stick frame houses weigh 50 tons for a 186m2 unit. If that 186m2 house was rebuilt with modern insulated rammed earth, its weight would be 150 tons, which is considerably more difficult to blow over. Every year trailers and houses are destroyed and replaced with identical lightweight units. We can do better. Many houses are destroyed by termites, carpenter ants, powder post beetles, rot and mold, all of which attack the wood framing. Organic materials by their nature decompose. Houses destroyed this way are typically rebuilt with wood framing with an added host of toxins to make the wood less appealing to nature’s decomposition agents. In all of these circumstances the opportunity for modern rammed earth construction is to provide resilient, durable, healthy and sustainable environments that have a better chance of weathering and surviving extreme weather and pests. [8]

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3.5. THE FUTURE OF RAMMED EARTH 3.5.1. PREFABRICATION In general, rammed earth as a construction technique needs an intense amount of work and ability. In this sense, the industrialization in the production of rammed walls would rationalize the costs of labour and execution times, as well as provide improvements in areas such as earth and water metering, control of quality of execution, in particular the degree of compaction and, of course, the final finish. Prefabrication allows the integration of electrical and air conditioning installations, increasing the qualities of the earth. Prefabrication is a step towards the modernization of earth construction, which has inherent a strong added value of sustainability on which we try to open new ways to facilitate its use in building and as a part of the architectural design.

FIG. 54 PREFABRICATED PANELS OF RAMMED EARTH WITH TONGUE-AND-GROOVE BORDERS [31]

3.5.1.1. Advantages Prefabrication of rammed earth has decisive advantages over in situ, typical of the rationalized technical work:     

The production can be carried out regardless of the weather outside, avoiding interruptions by the weather. Enforcement yields can be calculated with great precision, optimizing working methods. Working time on site is reduced. Work planning and coordination of interventions in the construction site are improved, reducing delivery times. The quality control processes are improved and as the final quality of the piece (dosages, degree of compaction, final texture, etc.). [31]

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3.5.1.2. Disadvantages Disadvantages are, especially, the fact that all should be planned well throughout the construction process to be performed in workshops prior to the execution of prefabricated rammed earth, a process that use to be complex and costly. In one application this disadvantage is offset standardized although individualized leads to design limitations. One of the difficulties of prefabricated rammed earth is transportation, since the lack of ductility of the material requires conditions of packaging, storage, loading, unloading and transfer more carefully than for example require the precast reinforced concrete pieces. Yet experience has shown that this aspect is not a problem. Prefabricated parts of up to 7000 kg were transported over long distances beyond of 800 km. The cost of building with this technique is generally more expensive than executed walls "in situ". The transport of prefabricated elements, sometimes over long distances, involves extra costs in comparison with transportation of separately materials in conventional construction. Transporting materials over great distances poses major ecological concerns, although it is a common practice in much of the materials commonly used in construction. In the case of rammed earth, transportation is offset in relation to other conventional materials such as brick or concrete, because the former has a balance of CO2 emissions much lower, one of the good points of this building material. For the execution of large projects of rammed earth, it is convenient to set a temporary prefabrication workshop next to the construction site. Thus also exploit local ground, another mentioned advantages of this method of construction. [31]

3.5.2. ADDITIVES AND SPECIAL TREATMENTS Nowadays chemistry allows us to modify earth in order to increase some properties as strength, durability, fire resistance, etc. Not only with artificial additives, but also with natural ones. Nevertheless, we should keep in mind that the more natural is the building process the less harmful for the environment. Moreover, they add significantly to cost. Thus, as a rule, it is only necessary to modify the characteristics of loam for special applications. As we can see in Fig. 55, additives that improve certain properties might worsen others. For instance, compressive and bending strength can be raised by adding starch and cellulose, but these additives also reduce the binding force and increase the shrinkage ratio, which is disadvantageous [12]. The precise quantities of additives often need to be determined empirically by trial and error for each particular situation. The results of laboratory tests often cannot be transferred directly to field practice, although they do provide useful guidance and a starting point for field tests. In the field, relatively simple and inexpensive tests such as observation of block durability on soaking in water and the use of a simple press to assess the load a block can carry in flexure can provide information on stabiliser requirements. As preparation of soil mixes and their use for building is often carried out under less rigorous conditions than for testing a reasonable increase in stabiliser dosage to compensate for this is recommended [32].

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FIG. 55 INFLUENCE OF VARIOUS ADDITIVES ON THE SHRINKAGE, BINDING FORCE, TENSILE BENDING FORCE AND COMPRESSIVE FORCE OF A SANDY LOAM [12]

3.5.2.1. Reduction of shrinkage cracks Because of increased erosion, shrinkage cracks in loam surfaces exposed to rain should be prevented. Shrinkage during drying depends on water content, on the kind and amount of clay minerals present, and on the grain size distribution of the aggregates. Addition of sand or larger aggregates to a loam reduces the relative clay content and hence the shrinkage ratio. The results of this method are shown in Fig. 56 and Fig. 57. In Fig. 56, a loam with 50% clay and 50% silt content was mixed with increasing amounts of sand until the shrinkage ratio approached zero. To insure comparability, all samples tested were of standard stiffness (according to German standard DIN 18952). Interestingly, a shrinkage ratio of 0.1% is reached at a content of about 90% sand measuring 0 to 2 mm diameter, while the same ratio is reached earlier when using sand having diameters of 0.25 to 1 mm, i.e. at about 80%. A similar effect can be seen in Fig. 58 with silty loam, where the addition of coarse sand (1 to 2 mm in diameter) gives a better outcome than normal sand with grains from 0 to 2 mm in diameter. Fig. 58 shows the influence of different types of clay: one series thinned with sand grains of 0 to 2 mm diameter with 90% to 95% pure Kaolinite, the other with Bentonite, consisting of 71% Montmorillonite and 16% Illite.

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FIG. 56 REDUCTION OF SHRINKAGE BY ADDING SAND TO A CLAYEY LOAM [12]

FIG. 57 REDUCTION OF SHRINKAGE BY ADDING SAND TO A SILTY LOAM [12]

FIG. 58 REDUCTION OF SHRINKAGE IN DIFFERENT CLAYS [12]

The simplest method for reducing shrinkage cracks in earth building elements is to reduce their length and enhance drying time. While producing mud bricks, for instance, it is important to turn them upright and to shelter them from direct sunlight and wind to guarantee a slow, even drying process. Another sensible method is to design shrinkage joints that can be closed separately, and which avoid uncontrolled shrinkage cracks.

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3.5.2.2. Stabilization against water erosion In general, it is unnecessary to raise the water resistance of building elements made from earth. If, for instance, an earth wall is sheltered against rain by overhangs or shingles, and against rising humidity from the soil through the foundation by a horizontal damp-proof course (which is necessary even for brick walls), it is unnecessary to add stabilizers. But for mud plaster that is exposed to rain, and for building elements left unsheltered during construction, the addition of stabilizers may be necessary. The stabilizers cover the clay minerals and prevent water from reaching them and causing swelling. Theoretically, a weather-resistant coat of paint is sufficient as protection, but in practice, cracks often appear on the surface or are created by mechanical action. Further, there is the danger of rainwater penetrating the loam, causing swelling and erosion. [12]

3.5.2.2.1. Cement, lime and bitumen The rule of thumb says that cement and bitumen as stabilizers are good for loam with less clay, and lime for clayey loams. This rule, however, does not take into consideration the type of clay. For instance, Montmorillonite and Kaolinite clay react quite differently: lime offers better stabilization with rich clayey loams, while cement gives better results with leaner loams. Furthermore, cement is more effective with Kaolinite and lime with Montmorillonite. In practice, it is always recommended that relevant tests be conducted. As with concrete, the maximum water resistance of cement-stabilized earth is reached after 28 days. These earth (in blocks or as rammed earth) must cure for at least seven days, and should not dry out too soon. If not protected against direct sun and wind, the blocks/walls must be sprayed by water while curing. To hasten and enhance the curing process, 20 to 40 g sodium hydroxide (NaOH) can be added to each litre of water. Similar effects can be obtained with about 10 g per litre of water of either NaSO4, Na2CO3 or Na2SiO2. [12]

3.5.2.2.2. Grain distribution Water resistance can also be raised by changing the grain distribution of silt and sand, as we can see in an erosion test using three mud bricks (shown in Fig. 59) onto which ten litres of water were poured for a period of two minutes. The brick in the middle, with high silt content, showed extreme erosion up to 5 mm depth. The brick on the right, with a higher clay content (ca. 30%) showed erosion up to 3 mm depth; the brick on the left, with the same clay content, but less fine and coarser sand, exhibited very little erosion. [12]

FIG. 59 EROSION TEST ON GREEN BRICKS. FONT: BUILDING WITH EARTH [12]

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3.5.2.2.3. Others 







Soda waterglass: (Na2O · 3-4 SiO2) is a good stabiliser for sandy loam, but it must be thinned with water in a 1:1 proportion before being added. Otherwise, micro cracks will occur which generate strong water absorption. Mineral and animal products: blood, urine, cow dung, manure, casein and animal glue have been used through the centuries to stabilise loam. In former times, oxblood was commonly used as a binding and stabilising agent. In Germany, the surfaces of rammed earth floors were treated with oxblood, rendering them abrasion-and wipe- resistant. Plant products: Plant juices containing oily and latex and derived from plants such as sisal, agave, bananas and Euphorbia herea, usually in combination with lime, are used as a stabilising coating with success in many countries. Artificial: Synthetic resins, paraffins, synthetic waxes and synthetic latex are all known to have a stabilising effect on loam. However, they are relatively expensive, prone to ultraviolet degradation, and because they act as vapour barriers, these stabilisers should be tested before use. [12]

3.5.2.3. Enhancement of binding forces Normally, no specific binding force is needed with loam as a building material. But if the binding force is insufficient, it can be increased by adding clay or by better preparation that is, by kneading and water curing. Mineral, animal and plant products that are usually added to enhance the weather resistance of loam also normally enhance its binding force although they may sometimes reduce it. Also, the binding force of lean loams can be increased by additives like whey, fat-free white cheese, fresh cheese, urine, manure, double-boiled linseed oil, or lime casein glue. The results have to be tested in each case before using these additives in a building element. [12]

FIG. 60 BALL DROPPING TEST TO DEMONSTRATE DIFFERENT BINDING FORCES. FONT: BUILDING WITH EARTH [12]

3.5.2.4. Increasing compressive strength The compressive strength of a mix is affected by the type and amount of preparation, as well as by the proportion of water used in the preparation, a fact that is neither well known nor well-researched. At the Institute for Building Technology of the Swiss Federal Institute of Technology in Zurich and at the Building Research Laboratory at the University of Kasel (Germany), it was proven that a slightly moist loam, when free from lumps and compacted in a soil block press, usually has a smaller compressive strength than the same loam combined with sufficient water, mixed by hand, and then simply thrown into a mould (as is done when making adobes). Other important fact is compaction, especially in rammed earth technique. Compacting loam under static force in order to increase its compressive strength is generally less effective than beating or ramming while vibrating (by dynamically applied forces). When a heavy object falls onto it, waves are generated, causing soil particles to

52

vibrate. This in turn creates movements that allow the particles to settle into a denser pattern. Furthermore, if there is sufficient water, clay minerals have the ability to form parallel, denser, and more ordered structures due to electrical forces, resulting in higher binding and compressive strength. [12]

Loam Silty

Sandy

Specific Weight [Kg/m3]

Vibration [rpm]

2003 1977 2005 2003 2009 2024

0 1500 3000 0 1500 3000

Compressive Strength [N/mm2] 3.77 4.11 4.17 2.63 2.91 3.00

TABLE 7 COMPRESSIVE STRENGTHS AFTER STATI AND DYNAMIC COMPACTION OF SANDY LOAM (CLAY 15%, SILT 29%, SAND 56%) AND SILTY LOAM (CLAY 12%, SILT 74%, SAND14%) [12]

FIG. 61 VIBRATING RAM [12]

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FIG. 62 DIFFERENT RAMS, MANUAL ABOVE AND MECHANICAL BELOW [12]

In earth construction, however, the maximum density or compaction, and therefore, the so-called optimum water content, do not necessarily lead to maximum density or compaction. Therefore the so-called optimum water content does not necessarily lead to the maximum compressive strength, nor is it the most decisive parameter. On the contrary, the decisive parameters are workability and binding force; hence it is recommended that loam should not be used with optimum water content as per DIN 18127, but instead with a water content somewhat higher than the optimum so derived. In fact, this so-called optimum water content may be treated, in practice, as a minimum water content. With compressed soil blocks, it has been shown that a water content 10% higher than the optimum gives better results than the so-called optimum. Therefore, the optimum water content does not usually result in maximum compressive strength. There is also discovered that if there is lesser compaction and higher water, then the same compressive strength may be achieved by using higher compaction and less water [33]. Loam for building normally has a compressive strength of 2 to 5 MPa. The permissible compressive stress for walls according to the German standard DIN 18954 is 3 to 5 MPa. In practice, it is very seldom required to enhance compressive strength, this being necessary only in highly stressed elements used in structures taller than two storeys (which are not permissible by most standards anyway). With earth components, the edge strength against impact is very important and often needs to be increased. Rigidity of corners against breakage depends upon compressive as well as bending tensile strength. This “edge impact strength” is very important during construction, when bricks or blocks are being transported, moved or stacked. The compressive strength of a loam type depends mainly upon its soil grain size distribution, water content, the static or dynamic compaction imparted to it, and the type of clay mineral present. If the sand and gravel particles are distributed so as to give a minimum packing volume, and the silt and clays are such that the inter-granular spaces of the sand and gravel are fully filled by them, then maximum density (and hence, compressive strength) has been achieved [12].

54

Using additives as cement, rammed earth may achieve even 30 MPa (value reached at the University Politechnika Warszawska). However, using cement is one of the things we try to avoid in sustainable construction, although rammed earth stabilized with cement contains considerably less cement than concrete itself.

3.5.2.5. Fibres Fibres are added to earth materials mainly to reduce shrinkage and improve tensile strength, although density is also lowered, reducing weight and compressive strength, and increasing thermal resistance. Fibres are commonly included in earth bricks and blocks, but rarely added to mortars. Fibres are not always added to earth bricks, and some proprietary materials do not contain them because their manufacturing processes involve relatively low moisture contents, leading to little subsequent shrinkage. The most common fibre in vernacular earth construction is straw, and this is also used in some modern materials. There is little significant difference in the properties of different cereal straws. Hemp, flax and other plant fibres are also sometimes used. Although finer and stronger than cereal straws, hemp fibres are harder to process and have a more significant value. [34] The oft-mentioned assumption that fibres always increase compressive strength is false. When fine fibres or hair are added in small amounts, tensile strength – and therefore compressive strength – is increased slightly. The addition of cut straw, however, has the opposite effect. Obviously, the length of the straw shoots should be no greater than the thickness of the building element. [12]

Straw [%/mass] 0 1 2 4 8

Weight [kg/m3] 1882 1701 1571 1247 872

Compressive strength [N/mm2] 2.2 1.4 1.3 1.1 0.3

TABLE 8 REDUCTION OF THE COMPRESSIVE STRENGTH OF LOAM BY ADDING CUT STRAW (5 CM) [12]

3.5.2.6. Increasing thermal insulation The U-factor or U-value, is the overall heat transfer coefficient that describes how well a building element conducts heat or the rate of transfer of heat (in watts) through one square metre of a structure divided by the difference in temperature across the structure. A smaller U-factor is better at reducing heat transfer. R-value is the reciprocal of U-factor. [35] Rammed earth generally has a low resistance to heat transfer, with a dry conductivity in the range of 0.8-1.0 W/mK. This value is dependent on the specific density and moisture content of a rammed earth mixture. In general, the thermal conductance increases with density and so does compressive strength. Thus a balance can be struck between thermal performance and structural strength. As moisture content increases, so does thermal conductivity and its thermal mass (see definitions in Table 9).

55

Property

Thermal mass

Thermal conductivity

Definition In building design, thermal mass is a property of the mass of a building which enables it to store heat, providing "inertia" against temperature fluctuations. Scientifically, thermal mass is equivalent to thermal capacitance or heat capacity, the ability of a body to store thermal energy. The insulating capability of a material is measured with thermal conductivity. Low thermal conductivity is equivalent to high insulating capability (R-value).

SI unit

J/K

k

TABLE 9 SOME IMPORTANT DEFINITIONS FOR THERMAL BEHAVIOUR OF BUILDING ELEMENTS

The thermal resistance of rammed earth alone is not great enough retain heat in a cold climate building. Obtaining a meagre R-20 would require a 3.5m wall thickness. Cold climate design thus dictates that rammed earth should be coupled with thermal insulation to attain higher thermal resistance. Rammed earth’s relatively low thermal resistance is countered by its large thermal mass. Thermal mass allows a material to absorb heat during warm periods and then release this absorbed heat over cooler eriods that follow. When applied to a building envelope, thermal mass simply mitigates internal temperature fluctuations, as shown in Fig. 63 Visual explanation of thermal mass transmission effect. large external temperature fluctuations on the right are moderated to lesser internal fluctuations on the left side. Overall, this increases the effective winter design temperature and decreases the effective summer design temperature, which reduces the energy required to condition the internal building space.

FIG. 63 VISUAL EXPLANATION OF THERMAL MASS TRANSMISSION EFFECT. LARGE EXTERNAL TEMPERATURE FLUCTUATIONS ON THE RIGHT ARE MODERATED TO LESSER INTERNAL FLUCTUATIONS ON THE LEFT SIDE [36]

The thermal insulation of loam can be increased by adding porous substances such as straw, reeds, seaweed, cork and other light plant matter. Naturally or artificially foamed mineral particles like pumice, lava, expanded clay, foamed glass, expanded perlite and foamed plant matter like expanded cork can also be added. Waste

56

products like sawdust, wood shavings, and husk of grains can also be used, but given their higher density, they exhibit inferior insulating properties. The more porous the mixture, the lighter it is and the greater its thermal insulation.

3.5.2.6.1. Lightweight straw loam To briefly know the order of magnitude, if 10 parts of cut straw are mixed with thick loam slurry made of 2 parts of dry clayey loam and 1 part of water, this will give a mixture with a dry density of about 1,300 kg/m and a k value of about 0.53 W/mK. Thus, a typical element of this material with a thickness of 14 cm covered with 2 cm lime plaster on both sides gives a U-value of 2.1 W/m3K. On the other hand, if a U-value of 0.5 W/m2K is to be achieved (as generally desired or required by building codes in most central and northern European countries today), then this wall would have to be 0.95 m thick. Even if the straw content were to be increased threefold, this material is unacceptable for a thickness of 14 cm. The following points are to be kept in mind when working with lightweight straw loam, for lightweight straw loam has certain undeniable disadvantages in comparison with pure loam: a) In a moderate or humid climate, fungus growth occurs after only a few days, emitting a characteristic strong smell. This can, in extreme cases, give rise to allergies. Therefore, good ventilation during construction must be provided so that building components dry out quickly. After the walls have dried completely, which might take several months, or even a year or more, depending upon thickness and climate, the fungus stops producing spores. However, spore formation may be reactivated if water permeates the walls either from the outside through leakage, or from inside through condensation. Fungus growth can be inhibited by adding lime or borax, but this has the following disadvantages:  Binding force and compressive strength are significantly decreased.  Hands become irritated while working with this mixture.  Walls thicker than 25 cm may appear dry on the surface, even though they are rotting within. b) The surface strength of the mix for a wall with a density of less than 600 kg/m 3 is usually too low to effectively grip nails or dowels, as is often required. Since two layers are necessary, plastering is more laborious, sometimes with some reinforcement in between. c) When drying, vertical settling occurs, leading to gaps on top of wall elements. These must carefully be filled later on in order to prevent heat and sound bridges and air infiltration. d) Working with this material is fairly laborious. Without special machines for mixing and transportation, the labour input for a typical 30-cm-thick wall is about 6 h/m (20 h/m). This is four times the labour required for typical brick masonry work. The disadvantages mentioned above can be avoided if porous mineral aggregates are used instead of straw, as discussed in the following section. The potential advantages of lightweight straw loam are the low material costs involved, and the fact that it can be worked without investments in special tools and machinery. It is especially appropriate, hence, for do-it-yourself construction.

57

3.5.2.6.2. Lightweight mineral loam In order to increase thermal insulation, porous mineral aggregates can be added to loam as an alternative to straw; these include expanded clay, foamed glass, expanded lava, expanded perlite and pumice. It is possible to achieve a shrinkage ratio of 0 (i.e., to eliminate shrinkage altogether) by choosing the right proportion of aggregates. All other techniques of earth construction require consideration of shrinkage. In comparison with straw loam, the vapour diffusion resistance is two to three times higher and, therefore, the probability of condensation of water within the wall is low. Another advantage of the material is that the mixture can be pumped into a formwork, thereby greatly reducing labour input. As investments on machines are higher this method is recommended only for larger construction projects. The densities generally achieved vary from 500 to 1,200 kg/m3.

3.5.2.6.3. Additives In some industrialised countries, expanded clay is a low-cost and easily available additive. It has a bulk density of about 300 kg/m3, and is produced by burning loam in rotary ovens at temperatures up to 1200°C without any other additive for foaming. Foaming occurs due to the sudden heating, which causes the water of crystallisation and the pore water to evaporate, creating an expansion in the mass (similar to making pop-corn). The surface of these expanded clay balls melts and is sintered. Nearly all of the pores in these expanded clay balls are closed, and are therefore unsusceptible to water and frost. The equilibrium moisture content by volume is only 0.03%. Foamed glass has characteristics similar to expanded clay, but has a lower bulk density. It can be produced by recycling glass with additional foaming agents. Expanded perlite is produced from volcanic rock (found in Europe, on the Greek island of Milos and in Hungary). It contains 3% to 6% chemically bound water, and when it is heated up suddenly to 1000°C, this water evaporates and enlarges the former value 15 to 20-fold. The bulk density may be as low as 60 kg/m3, the k-value is 0.045 W/mK. The vapour diffusion resistance is about 2.7. The specific heat is 1000 J/KgK. With a material of bulk density 90 kg/m3, a k-value of 0.05 W/mK is achieved. The thermal insulation properties of lightweight mineral loam depend mainly on its density and are equal to that of lightweight straw loam if the density is higher than 600 kg/m3. For mixtures below 600 kg/m3, the thermal insulation properties of lightweight mineral loams are somewhat better than those of lightweight straw loams, since straw has a higher equilibrium moisture content, and therefore more moisture, which reduces insulation. The equilibrium moisture content of rye straw at a relative humidity of 50% and a temperature of 21°C, for instance, is 13%, whereas under the same conditions, it is only 0.1% in the case of expanded clay. [12]

3.5.2.6.4.Design Note that thermal mass is only effective at normalizing indoor temperatures when it is exposed to both an outdoor energy source and the indoor environment. With this in mind, window design size has an opposite effect on the two systems; increasing window size will increase any internal thermal mass’s exposure to solar radiation while it decreases the exposed area of envelope thermal mass. In general, increased window size leads to larger conductive heat transfer but also large solar gains. Thus, a “passive solar” home design might focus on using internal thermal mass to capture solar gains through large, sun-facing windows, sized such that these gains

58

outweigh or balance the loss in envelope efficiency. A rammed earth home design might focus less on solar gains and more on surface exposure. Deciding which design style is more effective is difficult and likely climate dependent, though the answer could be found through situation-specific building simulation. [36]

59

4. SOIL TESTING Whether the aim is to build a single house or to start a production unit for soil blocks or rammed earth, it is essential to test the soil used, not only in the beginning, but at regular intervals or each time the place of excavation is changed, as the soil type can vary considerably even over a small area. Basically there are two types of tests:  

Indicator or field tests, which are relatively simple and quickly done. Laboratory tests, which are more sophisticated and time consuming.

In certain cases, soil identification on the basis of experience can be sufficient for small operations, but normally some indicator tests are indispensable. They provide valuable information about the need for laboratory tests, especially if the field tests give contradicting results. Not all the tests need to be carried out, as this can be tiresome, but just those that give a clear enough picture of the samples, to exclude those that show deficiencies. This is not only necessary to achieve optimum material quality, but also to economize on costs, material, stabilizers, manpower and energy input. It should further be remembered that soil identification alone does not provide assurance of its correct use in construction. Tests are also necessary to evaluate the mechanical performance of the construction material.

60

4.1. TRADITIONAL SOIL TESTING

Collecting samples

Indicator or field tests

Odour test

Touch test

• The soil is best excavated directly at the building site and several holes are dug in an area that is big enough to supply all the required soil. • First, the topsoil containing vegetable matter and living organisms is removed (unsuitable for construction). • The soil samples are then taken from a depth of up to about 1.5 m for manual excavation, or up to 3 m if a machine will be doing the work. • A special device, an auger, is used to extract samples from various depths. Each different type of soil is put on a different pile. • The thickness of each layer of soil, its colour and the type of soil, as well as an accurate description of the location of the hole should be recorded on labels attached to each bag of soil taken for testing. Equipment: none Duration: few minutes Immediately after removal, the soil should be smelt, in order to detect organic matter (musty smell, which becomes stronger on moistening or heating). Soils containing organic matter should not be used or tested further. Equipment: none Duration: few minutes After removing the largest particles (gravel), a sample of soil is rubbed between the fingers and palm of the hand. A sandy soil feels rough and has no cohesion when moist. A silty soil still feels slightly rough, but has moderate cohesion when moist. Hard lumps that resist crushing when dry, but become plastic and sticky when moistened indicate a high percentage of clay. Similar tests can be done by crushing a pinch of soil lightly between the teeth (soils are usually quite clean!).

61

Equipment: knife Duration: few minutes Lustre test A slightly moist ball of soil, freshly cut with the knife will reveal either a dull surface (indicating the predominance of silt) or a shiny surface (showing a higher proportion of clay).

FIG. 64 [6]

Adhesion test

Equipment: knife Duration: few minutes When the knife easily penetrates a similar ball of soil, the proportion of clay is usually low. Clayey soils tend to resist penetration and to stick to the knife when pulled out.

FIG. 65 [6]

Equipment: bowl of water or water tap Duration: few minutes Washing test When washing hands after these tests, the way the soil washes off gives further indication of its composition: sand and silt are easy to remove, while clay needs to be rubbed off.

62

Equipment: two screens with wire mesh of 1 mm and 2 mm Duration: half an hour

Visual test

Water retention test

With the help of the screen the dry gravel and sand particles should be separated on a clean surface to form two heaps. Crushing of clay lumps may be necessary beforehand. By comparing the sizes of the heaps a rough classification of the soil is possible. A. The soil is either silty or clayey if the "silt + clay" pile is larger; a more precise classification requires further tests. B. Similarly the soil is sandy or gravelly, if the "sand + gravel" pile is larger. C. and D. Further sieving with a 2 mm mesh screen will reveal whether the soil is gravelly or sandy. In the case of sandy or gravelly soil, a handful of the original material (before sieving) should be moistened, made into a ball and left to dry in the sun. If it falls apart as it dries, it is called "clean", and thus unsuitable for earth constructions, unless it is mixed with other materials. If the soil is not "clean", the silt and clay pile should be used for the next tests. Equipment: none Duration: 2 minutes A sample of the fine material is formed into an egg-sized ball, by adding just enough water to hold it together but not stick to the hands. The ball is gently pressed into the curved palm, which is vigorously tapped by the other hand, shaking the ball horizontally. • When it takes 5 - 10 taps to bring the water to the surface (smooth, "livery" appearance), it is called rapid reaction. When pressed, the water disappears and the ball crumbles, indicating a very fine sand or course silt. • When the same result is achieved with 20 - 30 taps (slow reaction), and the ball does not crumble, but flattens on pressing, the sample is a slightly plastic silt or silty clay. • Very slow or no reaction, and no change of appearance on pressing indicate a high clay content.

FIG. 66 [6]

63

Dry strength test

Equipment: oven, if no sun available Duration: four hours for drying 2 to 3 moist samples from the previous test are slightly flattened to 1 cm thickness and 5 cm Φ and allowed to dry completely in the sun or in an oven. By attempting to pulverize a dry piece between thumb and index finger, the relative hardness helps to classify the soil: • If it is broken with great difficulty and does not pulverize, it is almost pure clay. • If it can be crushed to a powder with a little effort, it is a silty or sandy clay. • If it pulverizes without any effort, it is a silt or fine sand with low clay content. Equipment: flat board, approx. 30 x 30 cm Duration: 10 minutes

Thread test

Another moist ball of olive size is rolled on the flat clean surface, forming a thread. If it breaks before the diameter of the thread is 3 mm, it is too dry and the process is repeated after remoulding it into a ball with more water. This should be repeated until the thread breaks just when it is 3 mm thick, indicating the correct moisture content. The thread is re-moulded into a ball and squeezed between thumb and forefinger. • If the ball is hard to crush, does not crack nor crumble, it has a high clay content. • Cracking and crumbling shows low clay content. • If it breaks before forming a ball, it has a high silt or sand content. • A soft spongy feel means organic soil. FIG. 67 [6]

Equipment: none Duration: 10 minutes

Ribbon test

With the same moisture content as the thread test, a soil sample is formed into a cigar shape of 12 to 15 mm thickness. This is then progressively flattened between the thumb and forefinger to form a ribbon of 3 to 6 mm thickness, taking care to allow it to grow as long as possible. • A long ribbon of 25 to 30 cm has a high clay content. • A short ribbon of 5 to 10 cm shows low clay content. • No ribbon means a negligible clay content. FIG. 68 [6]

64

Equipment: cylindrical glass jar of at least 1 litre capacity, with a flat bottom and an opening that can be just covered with the palm; centimetre scale Duration: 3 hours Sedimentation test

The glass jar is filled quarter full with soil and almost to the top with clean water. The soil is allowed to soak well for an hour, then with the opening firmly covered, the jar is shaken vigorously and then placed on a horizontal surface. This is repeated again an hour later and the jar then left standing undisturbed for at least 45 minutes. After this time, the solid particles will have settled at the bottom and the relative proportions of sand (lowest layer), silt and clay can be measured fairly accurately. However, the values will be slightly distorted, since the silt and clay will have expanded in the presence of water.

FIG. 69 [6]

Laboratory tests

Equipment: long metal or wooden box with internal dimensions 60 x 4 x 4 cm (l x b x h), open on top; oil or grease; spatula Duration: 3 to 7 days

Linear shrinkage test

The inside surfaces of the box are greased to prevent the soil from sticking to them. A sample of soil with optimum moisture content is prepared (ie when squeezing a lump in the hand, it retains the shape without soiling the palm, and when dropped from about 1 metre height, breaks into several smaller lumps). This soil mix is pressed into all corners of the box and neatly smoothened off with the spatula, so that the soil exactly fills the mould. The filled box is exposed to the sun for 3 days or left in the shade for 7 days. After this period, the soil will have dried and shrunk, either as a single piece or forming several pieces, in which case they are pushed to one end to close the gaps. The length of the dried soil bar is measured and the linear shrinkage is calculated as follows: ((Length of wet bar) - (Length of dried bar))/(Length of wet bar) x 100 To obtain good results in construction, the soil should shrink or swell as little as possible. The more the soil shrinks, the larger is the clay content, which can be remedied by adding sand and/or a stabilizer, preferably lime. FIG. 70 [6]

65

Equipment: a set of standardized sieves with different meshes (e.g. 6.3 mm, 2.0 mm, 0.425 mm and 0.063 mm); flat water container below the sieves; 2 small buckets, one filled with water; stove or oven for drying samples; 2 to 5 kg balance with an accuracy of at least 0.1 g Duration: 1 to 2 hours Wet sieving test

A 2 kg soil sample is weighed dry, placed in the empty bucket and mixed with clean water. The water-soil mix, well stirred, is poured into the sieves, which are placed in descending order one on top of the other, with the finest mesh at the bottom, below which is the flat container. The bucket is rinsed clean with the remaining water, which is also poured into the sieves. Each sieve will have collected a certain amount of material, which is dried by heating on the stove or in the oven, then weighed accurately and recorded. The fine particles in the bottommost container is a mixture of silt and clay, which cannot be separated by sieving. This is carried out by the next test.

FIG. 71 [6]

Equipment: a 1-litre graduated glass measuring cylinder, with an inside diameter of about 65 mm; a circular metal disk on a stem, which can be lowered down inside the cylinder; a rubber tube and heat resistant drying dishes for siphoning; a watch; a pinch of salt; stove or oven and balance, as in previous test Duration: 1 to 2 hours

Siphoning test

A dry sample of 100 g of the fine material from the previous test is carefully weighed and put into the cylinder. A pinch of salt is added, to improve dispersion of the clay particles, and water is filled up to the 200 mm mark. With the cylinder kept firmly closed with the palm of the hand, the contents are shaken vigorously until a uniform suspension of the grains is achieved. The cylinder is placed on a firm level surface and the time taken. After 20 minutes, the metal disk is carefully lowered down to cover the material that has settled at the bottom of the cylinder, without disturbing it. The clay, which is still in suspension, is removed by siphoning off the liquid, which is subsequently dried out and the residue weighed. The weight in grams is also the percentage of clay in the sample.

FIG. 72 [6]

66

Grain size distribution analysis

Atterberg limit tests

With the results of the wet sieving and siphoning tests of one sample showing the relative proportions of the various constituents, as defined by their particle sizes, several points can be plotted on a chart. A curve is then drawn so that it passes through each point successively, giving the grain size distribution of that particular soil sample. This can tee repealed for other samples on the same chart, showing the range of soil types analysed. The chart below shows an example of a gravelly soil (G) and a clay soil type (C). The horizontally shaded area indicates the types of soils that are suitable for rammed earth construction, while the vertically shaded area shows appropriate soils for compressed block production. The overlapping area is thus good for most soil constructions, so that a curve (I) running through the middle symbolizes a soil of ideal granulation. The purpose of this exercise is to determine whether the available soil is suitable for building. If the soil is too gravelly, the gaps between the particles are not properly filled, the soil lacks cohesion and is consequently very sensitive to erosion. If the soil is too clayey, it lacks the large grains that give it stability, and is thus sensitive to swelling and shrinkage. An optimum grain size distribution is one in which the proportion of large and small grains is well balanced, leaving practically no gaps, and sufficient clay particles are present to facilitate proper cohesion. If the tests reveal a poor grain size distribution, it can be corrected to some extent by: • sieving the gravelly fraction, if the soil contains too much coarse material; • partly washing out the clayey fraction, if finer particles are in excess; • mixing soil types of different granular structure. These tests, developed by the Swedish scientist Atterberg, are needed to find the respective moisture contents at which the soil changes from a liquid (viscous) to a plastic (mouldable) state, from a plastic consistency to a soft solid (which breaks apart before changing shape, but unites if pressed), and from this state to a hard solid. While the previous tests determined the quantity of each soil constituent, the Atterberg tests show which type of clay mineral is present. This has an influence on the kind of stabilizer required. For all practical purposes, the determination of the "liquid limit" and "plastic limit" is sufficient, the other Atterberg limits are not so important. However, the determination of the Atterberg limits is usually carried out with the "fine mortar" fraction of the soil, which passes through a 0.4 mm sieve. This is because water has little effect on the consistency of larger particles.

FIG. 73 [6]

FIG. 74 [6]

67

Liquid limit test: Equipment: a curved dish, about 10 cm in diameter and 3 cm deep, with a smooth or glazed inner surface; a grooving tool (as illustrated); a metal container with tightly fitting cover (eg large pill box), a drying oven which maintains a temperature of 110° C; a balance, accurate to at least 0.1 g, preferably to 0.01 g. Duration: about 10 hours A sample of fine soil (about 80 g) is mixed with drinkable water to a consistency of a thick paste and evenly filled into the dish such that the centre is about 8 mm deep, gradually diminishing towards the edge of the dish. This is divided into two equal parts by drawing the grooving tool straight through the middle, making a V-shaped groove (of 60° angle) and a 2 mm wide gap at the bottom. Alternatively, a knife can be used. The dish is held firmly in one hand and tapped against the heel of the other hand, which is held 30 to 40 mm away. The motion must be a right angles to the groove. If it takes exactly 10 taps to make the soil flow together, closing the gap over a distance of 13 mm, the soil is at its liquid limit. If it takes less than 10 taps, the soil is too moist; more than 10 taps means that it is too dry. The moisture content must then be corrected, whereby moist soils can be dried by prolonged mixing or adding dry soil. The process is repeated until the liquid is found. With an accurate balance, it is sufficient to take just a small sample of soil, scraped off from a point close to where the groove closed. The sample is put into the container, which is tightly covered and weighed before the moisture can evaporate. The soil container is then put into the 110°Coven until the veil is completely dry. This may take 8 -10 hours and can be checked by weighing several times, until the weight remains constant. Knowing the wet (W1) and dry weight (W2) of the soil and container, and the weight of the clean dry container (WC), the liquid limit, expressed as the percentage of water in the soil, is calculated as follows: Liquid Limit=Weight of Water/Weight of oven dried soil x 100 L=(W1-W2)/(W2-WC) x 100 % Some examples of liquid limits are: Sand: L = 0 to 30 Silt: L = 20 to 50 Clay: L= over 40

FIG. 75 [6]

68

Plastic limit test: Equipment: a smooth flat surface, e.g. glass plate 20 x 20 cm; a metal container, drying oven and balance, as for the liquid limit test. Duration: about 10 hours About 5 g of fine soil is mixed with water to make a malleable but not sticky ball. This is rolled between the palms of the hands until it begins to dry and crack. Half of this sample is rolled further to a length of 5 cm and thickness of 6 mm. Placed on the smooth surface, the sample is rolled into a thread of 3 mm diameter (see illustration for Thread test). If the sample breaks before the diameter reaches 3 mm, it is too dry. If the thread does not break at 3 mm or less, it is too moist. The plastic limit is reached, if the thread breaks into two pieces of 10 - 15 mm length. When this happens, the broken pieces are quickly placed in the metal container and weighed (W1). The next steps of drying and weighing the soil and container are the same as for the liquid limit test, determining the values W2 and WC. The whole procedure is repeated for the second half of the original sample. If the results differ by more than 5 %, the tests must be repeated one again. The plastic limit is calculated in the same way as the liquid limit: Plastic Limit = Weight of Water/Weight of oven dried soil x 100 P=(W1-W2)/(W2-WC) x 100 % Plasticity Index: The plasticity index (PI) is the difference between the liquid limit (L) and plastic limit (P): PI=L-P The simple mathematical relationship makes it possible to plot the values on a chart. The advantage is that the areas can be defined in which certain stabilizers are most effective. It should, however, be noted that laterite soils do not necessarily conform to this chart. There is in fact no substitute for practical experimentation, using the recommended stabilizers to begin with, and starting with small dosages.

FIG. 76 [6]

TABLE 10 TRADITIONAL SOIL TESTING. BASED ON [37]

69

4.2. MODERN SOIL TESTING At present very few countries have developed standard tests specifically suited to rammed earth. Use is thus often made of tests originating in other disciplines such as concrete construction and road construction. Literature concerning the conservation of earthen structures often lacks any scientific knowledge of the material. These considerations point at the necessity of taking in account non/minor destructive diagnosis techniques (N-MDT) with the objective to evaluate, onsite, the state of conservation of earthen heritage. This could provide useful information on adequate conservation methods. [38] Techniques based on mechanical criteria Simple flat jack Double flat jack Shear test Hole drilling FreD Pressumeter/Dilatometer

Techniques based in (acoustic and electromagnetic) waves propagation Ultrasonic test Sonic test Impact echo test Infrared thermography Radar Geoelectric techniques

Other techniques Tomographic techniques Endoscopy Dynamic characterization Monitoring Penetration resistance Sphere impact Rebound tests Pull-out test or helix test

TABLE 11 SOME N-MDT TECHNIQUES FOR IN SITU ESTIMATION OF EARTHEN MATERIALS [38]

FIG. 77 HOLE DRILLING TEST [38]

70

5. SIMPLE COMPRESSIVE STRENGTH TESTS In this chapter we are going to analyse and compare several compressive strength tests of rammed earth specimens, which have been made in different years throughout the world. The chosen tests can be found in the next publications: Tests Nº 1 2 3 4 5 6 7 8 9

Name Arquitecturas de tapia The strength of unsterilized rammed earth materials The use of cement stabilised rammed earth for building a vernacular modern house Durability for stabilized earth concrete under both laboratory and climatic conditions exposure Advances on the assessment of soil suitability for rammed earth Rammed earth construction with granitic residual soils: The case study of northern Portugal Effect of moisture content on the mechanical characteristics of rammed earth In situ mechanical investigation of rammed earth: calibration of minor destructive testing Optimization of three new compositions of stabilized rammed earth incorporating PCM: Thermal properties characterization and LCA

Source [1] [39] [40] [41] [42] [43] [44] [38] [19]

TABLE 12 SIMPLE COMPRESSIVE STRENGTH TESTS AND THEIR PUBLICATIONS

71

5.1. PARTICLE SIZE DISTRIBUTION 5.1.1. Introduction There are several different types of earth according to the quantities of the following components: gravelly earth, sandy earth, silty earth and clayey earth. This particle size distribution will give different physics properties to the soil mixture.

FIG. 78 PARTICLE SIZE DISTRIBUTION [45]

72

FIG. 79 PHYSICS PROPERTIES OF EARTH [45]

In order to compare the particle size distribution of a soil with a model, we might use an empiric parable as Fuller’s parable. Then it’s easier to notice which sizes are in either excess or lack.

FIG. 80 GRADING CURVE OF THE SOIL USED IN THE SIMPLE COMPRESSIVE TEST AT TEST NUMBER 1 (DISCONTINUOUS LINE). FULLER PARABLES (CONTINUOUS LINE) OF MAXIMUM COMPACITY FOR GRAIN SIZE BETWEEN 40 AND 20 MILLIMIETRES [1]

In addition, we can give a "name" to the soil type according to its grain, following the methodology of USCS (Unified Soil Classification System) [46]: For granular soils, acronyms are G (gravel), S (sand), W (well graded) and P (poorly graded). For fine soils nomenclature is M (silt), C (clay), H (high compressibility) and L (low compressibility).

73

And for organic soils they are OH (organic soil of high compressibility), OL (organic soil of low plasticity) and Pt (peat). In our case, we used an Excel spreadsheet made by Jordi González Boada (www.jordigonzalezboada.com) to classify soils in which this classification had not been given. Despite in some tests there was lack of data.

FIG. 81 CASAGRANDE'S PLASTICITY CHART, SHOWING SEVERAL REPRESENTATIVE SOIL TYPES (DEVELOPED FROM CASAGRANDE, 1948, AND HOWARD, 1977)

The distribution of fractions between significant sizes (diameters), with characteristic properties is as follows: GRAVEL 63mm>d>2mm SAND 2mm>d>0.063mm SILT 0.063mm>d>0.002mm CLAY d<0.002mm FIG. 82 SIGNIFICANT DIAMETERS [47]

IPxM According to Michel [48], the best earth soils for stabilization are those with low plasticity index (PI) and the product (PI x M) in the vicinity of 500–800, where M is the percentage of the mortar (%clay).

Sand and gravel (% by mass) Silt (% by mass) Clay (% by mass) Cement (% by mass)

HB195 [49] 45-75 10-30 5-20 4-12

Walker et al. [50] 45-80 10-30 5-20 4-12

TABLE 13 SUMMARY OF THE MATERIAL REQUIREMENTS FROM SOME REFERENCE BOOKS IN EARTH CONSTRUCTION [42]

74

5.1.2. Tests’ table % CLAY

% SILT

% SAND

% GRAVEL

Tests Nº

Soil

1

1.1

2

2.1

10

17

53

20

3 4

3.1 4.1 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 6.1 6.2 6.3 6.4 7.1 7.2 7.3 7.4 7.5

33 18 5 30 15 30 40 10 10 20 30 5 6 5 4 12 5 4 9 10 10 26,2 4 42,5

42 18 25 0 15 20 20 15 5 0 10 25 14 15 14 12 30 35 38 30 22

25 64 50 50 50 20 20 50 40 60 20 50 45 59 60 53 49 59 50 12 43

0 20 20 20 20 20 25 45 20 40 20 35 21 22 23 16 2 3 48 25

9,28

64,48

0

0

50

7,5

5

6

7

8

8.1

9

9.1

PI x M

Standard

USCS

NLT 104/72

GP GM SM

644 15.5 414 145.5 402 736 53 79 242 699 20 LNEC E 196 [13] 132

SM SM SM SC

TABLE 14 GRAIN SIZE DISTRIBUTION IN PERCENTAGE, PI·M AND USCS NOMENCLATURE OF THE ANALYSED TESTS

5.1.3. Grain size distribution: conclusions It is crucial to state that the majority of the studies available in the literature are based on specific soil mixes, and hence the results are valid only for those mixes. Considering the endless variety of existing soils, drawing conclusions valid for any soil type from the results of a fraction of samples seems an impossible task. Rules based on particle size distribution that can predict the mechanical performance of any soil mix are not considered suitable for the assessment of soil for rammed earth. [42] It is demonstrated that there is no single optimum particle size distribution for earth construction. The best distribution is one which maintains a balance between all sizes so that optimal compaction. Taking as an example the methodology used in the test nº1 [1], it is a rule of good practice to compare the grading curve with a theoretical curve (see Fig. 80) and try to get through the necessary corrections to turn our curve as much alike as possible to the theoretical curve.

75

It is underlined in most tests that a soil classification is not used, such as SUCS, and moreover, insufficient data exist to get it ourselves (only 3 of the 9 tests studied offer this classification). It is important for the future of the standardization of the earth construction, to obtain a simple classification which leads us to the rules and tests necessary for any particular soil. This is because, as has been repeated many times, the fundamental problem of regulating the earth building is that each soil is different and needs a different treatment and preliminary tests. Thus, a soil that could be suitable for the construction of compressed earth blocks or cob, to give some examples, may not be suitable for the technique of rammed earth. The PIxM indicator is not always a good indicator of the suitability of a soil for stabilization, because although it gives us a good result in 4.1 with a compressive strength of 15.4 MPa, gives us a score of 2.6 MPa for 5.9 soil (see Table 26). There is a remarkable difference between the two soils: the 4.1 does not contain gravel and 5.9 is 40% gravel. On the other hand, they have either similar Atterberg limits (Table 16), densities and storage conditions. We do not know the mineralogical composition of the soil 5 which may be also a decisive factor for this compressive strength result.

5.2. ATTERBERG LIMITS AND OTHER PARAMETRES 5.2.1. Introduction On the other hand, there are also other characteristic parameters of each soil related with grain size which in turn serve for classification: The uniformity coefficient 𝐶𝑢 =

𝐷60 𝐷10

[1]

It’s used to measure and assess the degree of distribution of particle sizes of a soil. The smaller is the coefficient, the more "uniform" or "bad graduate" will be the soil. Where Di is the particle size for which the (i%) by weight of the soil is smaller than it. When D10 is called "effective diameter". The bend coefficient 𝐶𝑐 =

𝐷30 2 𝐷10 · 𝐷60

[2]

It helps in the interpretation of how is the soil gradded, giving information about the balance between the various sizes. Where Di is the particle size for which the (i%) by weight of the soil is smaller than it. When D10 is called "effective diameter". SE: Sand equivalent (NLT-133/72)

76

The purpose of this test is to find out the possible existence of a dangerous granular material to contain excessive fines and simultaneously check the uniformity of the material used. The scope of the test is granulated soils with a small proportion of plastic material. SL: Shrinkage limit The shrinkage limit (SL) is the water content where further loss of moisture will not result in any more volume reduction. The test to determine the shrinkage limit is ASTM International D4943. The shrinkage limit is much less commonly used than the liquid and plastic limits. It is the minimum water content. A: Activity coefficient High activity signifies large volume change when wetted and large shrinkage when dried. Soils with high activity are very reactive chemically. Normally the activity of clay is between 0.75 and 1.25, and in this range clay is called normal. It is assumed that the plasticity index is approximately equal to the clay fraction (A = 1). When A is less than 0.75, it is considered inactive. When it is greater than 1.25, it is considered active.

HB195 [49] <35-45 <10-30

Liquid Limit Plasticity Index

Walker et al. [50] <45 <2-30

TABLE 15 SUMMARY OF THE MATERIAL REQUIREMENTS FROM SOME REFERENCE BOOKS IN EARTH CONSTRUCTION [42]

5.2.2. Tests’ table Tests Nº

Soil

% LL % LP % PI Cc Cu

1 4

1.1 4.1 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 6.1 6.2 6.3 6.4

23.1 31 15,6 26,1 18 24,8 34,5 15,4 17,3 22,3 38,5 15,4 34 27 28 30

5

6

18.3 17 12,5 12,3 8,3 11,4 16,1 10,1 9,4 10,2 15,2 11,4

19

4.8 14 3,1 13,8 9,7 13,4 18,4 5,3 7,9 12,1 23,3 4

11

% SE 16.8 64

% SL

A

10 0,77 0 6 3 5,1 7,1 2 2,4 3,5 7,1 0,2 27 23 26 22

Standard

AS 1012.17 [9]

NP 143 [14] and ASTM D 4943 [15]

TABLE 16 ATTERBERG LIMITS AND OTHER PARAMETERS OF THE ANALYSED TESTS

77

5.2.3. Atterberg limits and other parameters: conclusions In all the cases studied, the liquid limit is below 40, according to the standards. In the test nº5 we can observe that the two soils with higher liquid limit have the worst results in simple compressive strength (5.5 and 5.9). However, there is lack of data in 5 of the tests studied. It is very important to define the Atterberg limits in any case of building construction, as well as the other parameters shown in the table. Without this, we couldn’t compare other soil with this ones and expect the same behaviour. It could be completely different.

5.3. ADDITIVES 5.3.1. Tests’ table Tests Nº 1 2

3

Soil/ Batch 1.1 2.1 3.1

Unstabilised Unstabilised Unstabilised

3.2

Sand

3.3

3.4

4

5

6

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 5.1 to 5.5 5.6 5.7 5.8 5.9 5.10 6.1 to 6.4 6.5

Additive

Cement Water Sand Cement Water Sand Cement Cement Lime Lime Cement + Lime Cement + Lime Cement + Resin Cement + Resin Unstabilised Cement Cement Cement + Lime Cement + Lime Cement Unstabilised By alkaline activation of fly ash

Details

Portland 42.5N

Portland 42.5N

Cement: 46 MPA tested by AFNOR regulations [6] Resine: MEDALATEX, supplied by Granitex

Quantity

25% from the amount of earth 2.25kg 5% from the amount of earth 0.45kg 10% from the amount of earth 0.9l 50% from the amount of earth 4.5kg 8% from the amount of earth 0.72kg 10% from the amount of earth 0.9l 70% from the amount of earth 6.3kg 5% Cement 8% Cement 8% Lime 12% Lime 5% Cement + 3% Lime 8% Cement + 4% Lime 5% Cement + 50% Resin 8% Cement + 50% Resin 5% Cement 4,5% Cement 4% Cement +1% Lime 4% Cement +2% Lime 4,5% Cement

The stabilized soil was the soil Nº 7.3 Geopolymeric binder obtained

2,5% fly ash

78

from the alkaline activation of fly ash. 6.6

5% fly ash It should be noted that the activator constitutes all the liquid phase of the mixtures, and thus the activator/solids ratio assumed a fixed value, slightly inferior to the OWC of the original soil.

6.7

7

7.1 7.2 7.3 7.4 7.5

Unstabilised Hydraulic lime Unstabilised Unstabilised Hydraulic lime

9.1.1

Straw (2-3 mm) Lime (0-200 µm) PCM (6 µm)

9.1.2

Straw (2-3 mm) Alabaster powder PCM (6 µm)

9.1.3

Pneumtic fibbers Lime (0-200 µm) PCM (6 µm)

9

7,5% fly ash

NHL 3.5

2% hydraulic lime

NHL 3.5 Lime: Ca(OH)2 CalesPachs® CL80 S. PCM: the microencapsulted used was Micronal® DS 5001. Alabaster: a by-product of Alabaster Technology. PCM: the microencapsulted used was Micronal® DS 5001. Lime: Ca(OH)2 CalesPachs® CL80 S. Pneumatic fibbers: residue from tires. PCM: the microencapsulted used was Micronal® DS 5001.

8% hydraulic lime 7,50% Straw 10% Lime 10% PCM 7,5% Straw 10% Alabaster 0% PCM

10% Pneumatic fibbers 10% Lime 5% PCM

TABLE 17 ADDITIVES USED IN THE ANALYSED TESTS

5.3.2. Additives: conclusions In all the cases cement content is below 12% as say the standards in Table 13. Otherwise it starts to loose sense because the more cement or lime added to the mixture, the less sustainable and environmental friendly is the building technique. As a result of the test nº 4, the following classification of the different products used as earth stabilizers can be made; according to their good durability:     It is also important to note that the utilization of the resin as a protection material is not economic. It is practically eight times more expensive than the treatment by cement. In test nº 6 we can say that regarding the typical low clay content of granitic residual soils, the addition of cement seems to be an efficient stabilisation solution. However, the addition of cement results in an important increase of the embodied energy of rammed earth walls [51]. For example, Lax [52] demonstrates that for a specific case,

79

the embodied energy in stabilised rammed earth with 8% of cement is 1.84 times higher than in unstabilised rammed earth. In order to try to mitigate the environmental impact of stabilised rammed earth built with granitic residual soils, the authors have been developing an alternative stabilisation solution, which consists in the addition of a geopolymeric binder obtained from the alkaline activation of fly ash. This technique has been recently studied in the manufacture of mortars and concrete [53], which present enhanced environmental impact and durability over those manufactured with ordinary Portland cement [54]. The stabilisation of rammed earth by alkaline activation of fly ash was recently introduced in Cristelo et al. [55], which presented a composition study using the soil 7.1 here described, and where the compressive strength was the control parameter. The compressive strength of the tested mixtures varied between 3 N/mm2 and 23 N/mm2, when cured for periods between 1 and 7 days at 60ºC. These values are significantly higher than those required for rammed earth construction. This means that the content of geopolymeric binder can be further decreased in order to promote higher sustainability and lower cost of this stabilisation solution in SRE construction. Therefore, the major contribution of the test nº6, relatively to [55], is the use of lower fly ash contents and the curing at ambient temperature [56]. However, the maximum compressive strength reached was 1.09 MPa, which may not be enough for earth building construction according to the most of the standards shown in Table 25. Thermal energy storage in buildings can be implemented by sensible heat or by latent heat (with the inclusion of PCM: phase change material) to increase thermal inertia (test nº 9). Phase change materials (PCM) have been studied for thermal storage in buildings during the past 30 years [57]. PCM placed on the building facade can be daily cycled. Thus, during the day the PCM absorbs heat and consequently is melted. Then, during the night the heat is discharged through the solidification process. Finally, the LCA shows that incorporating microencapsulated PCM in the rammed earth increases up to 4.5 times the impact points of the material. For this reason, macroencapsulated PCM is recommended to improve the LCA results. The addition of stabilizers also increases around 1.5 time the impact points of the material, but the use of alabaster has 1.26 times less impact points than the lime. [19] Other interesting methodology carried out in test nº 9 is the optimization of rammed earth composition through a design of experiments software (DoE). The samples given by the DoE were evaluated through compressive strength tests. The optimums of these samples were then thermally The DoE allows maximum information with minimum number of experiments. Furthermore, the main objective of the DoE is to deduce which components influence the mechanical properties of the new rammed earth. The objective of this DoE is to quantify the variation of mechanical properties of the measured rammed earth, according to the percentage of each component used. [19]

80

5.4. METHOD OF PREPARING SAMPLES 5.4.1. Tests’ tables Tests Nº

Shape

Dimensions (cm)

Number of layers

Standard

1

Cilindrical

15,20 diameter 13.2 height

5

Modified Proctor NLT 108/72

2

Cilindrical

10 diameter 20 height

5

3

Cube

10 cm3

4

Parallelepiped

10x10x20

5 cm high layers 1 Modified Proctor NLT 108/72

5 6

Cilindrical

7

Cilindrical

8 9

Parallelepiped

Cilindrical

10 diameter 20 height 16 diameter 30 height 15 diameter 4x4x16

3 6 UNE-EN 196-1:2005

TABLE 18 METHOD OF PREPARING SAMPLES IN THE ANALYSED TESTS

Type of Rammer Tests Nº

1 2 3 4 5 6 7

Type

Weight of rammer [Kg]

Nº of blows per layer

4,535±0,01 4,5

60 15

Surface of rammer

Drop height

19,6±0,2 cm²

457±2 mm

Manual Static and simple compressive force of 15 MPa Jackhammer Automatic Proctor machine

2,2 kg of moist soil for each layer Proctor energy E=0,6 Kj/dm3

TABLE 19 TYPE OF RAMMER IN THE ANALYSED TESTS

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5.4.2. Method of preparing samples: conclusions The compacted layer thickness in in situ rammed earth walls is around 10 cm. Due to nature of compaction there is a density gradient in each layer, as the upper part of each layer is more compacted and therefore denser than the bottom. Layer thickness of the laboratory samples is about 5 cm, meaning that the material is more evenly compacted over the entire layer thickness. The clear disadvantage of this laboratory manufacturing strategy is that the simple is not representative of typical in situ material. Therefore, to correlate the results obtained from laboratory-fabricated cylindrical samples to the performance of in situ walls, a calibration is necessary. [44] Fortunately, almost all tests indicate what shape and dimensions are the tested specimens. Instead, we can see that each test used a different type specimens. This makes us think again about the need of normalization for each type of test, so that the results of the various tests are fully comparable. As for the type of rammer, we have two distinct options. On the one hand, a manual rammer, which should be used in cases where the traditional rammed earth is the method used in the construction for which the tests were conducted, usually restorations where you want to preserve the traditional style. However, whether to use pneumatic rams and more modern techniques, tests should be consistent. In any case, we believe the best standardization should go in relation to the energy applied and the amount of material per layer, in addition to having a standard machine, as described in test nº 7.

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5.5. STORAGE CONDITIONS OF SAMPLES UNTIL THE STRENGTH TEST 5.5.1. Tests’ table Tests Nº 1 2 3

Period of storage (days) 27 7 28

Humidity Temperature (%) (ºC) Air-dried

4

28

>70

5

28

≈68

7~18

6

27~35

57,5

20±2

7

Details

Air-dried

The samples were put on a tray and covered by a plastic sheet 2 curing methods: humid atmosphere for 28 days and 27 days in humid atmosphere and then immersed completely in water for 24h at 20ºC Unstabilised: 3 days unwrapped + 28 days stripped in ambient conditions. Stabilized with cement: 1 day un wrapped + 7 days wrapped in an impermeable membrane + 20 days striped in ambient conditions. Stabilized with cement+lime: 1 day unwrapped and wrapped for 21 days, as specified by Standards New Zealand [58]. The curing preiod was placed at UWA structures laboratory, protected from direct sunlight and rain, but without rigorously controlled conditions due to insufficient availability of the laboratory facilities. The stabilized samples were wrapped in plastic sheet after demoulding and cured for 28 days. After the sample achieved the moisture content desired, the specimen was covered in a plastic film for at least a week.

TABLE 20 STORAGE CONDITIONS OF SAMPLES IN THE ANALYSED TESTS

5.5.2. Storage conditions of samples until the strength test: conclusions Very different methods are used to preserve samples of rammed earth until the time of simple compressive test arrives. It is necessary therefore to establish a standard process that takes into account the following aspects: temperature and humidity of the storage area, whether or not to cover the sample and with what kind of material, storage time depending on the additives used. The hardening kinetics of fly ash geopolymeric binders, especially under mild ambient temperatures, is known to be slow, especially when compared with that of Portland cement. Therefore, a significantly higher strength levels can be expected for these mixtures, providing that some more curing time is allowed. Ongoing tests by the authors seem to show that the average compressive strength at 90 days can double the values obtained at 28 days.

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5.6. CHEMICAL AND MINERAL COMPOSITION OF EARTH 5.6.1. Introduction One of the most significant challenges to create a rammed earth standard is the fact, already discussed, that each region has a different type of soil. This also includes different chemical and mineralogical composition. Therefore, this should be studied carefully in all soils prior to construction. And thanks to his analysis we can know how to modify a floor to get the results we need.

MBA: Methylene blue adsorption Methylene blue adsorption (MBA) is a measure of the clay particle surface area, which is a function of clay type, and an indicator of the percentage for water adsorption by the clay, and hence, its percentage for swell when wetted. Surface area measurements are a direct reflection of clay mineralogy, but are an indirect reflection of expansively. [59] It’s demonstrated that methylene blue test is an effective indicator of the amount and type of clay present in soil and, therefore, it can help to differentiate between beneficial or harmful fines.

Seed et al. [60] Swelling Degree of potential (%) expansion >25 Very high 5-25 High 1.5-5 Medium 0-1.5 Low

Holtz [61] Plasticity index Degree of (PI) Expansion >35 Very high 25-41 High 15-28 Medium <18 Low

Proposed by [59] Methylene blue Degree of value (g/100 g) expansion >15 Very high 8-15 High 4-8 Medium 0-4 Low

TABLE 21 SEVERAL PARAMTERS FOR MEASURING DEGREE OF EXPANSION IN SOILS [59]

84

5.6.2. Tests’ tables Tests Nº

Soil

4

4.1 7.1 7.2 7.3 7.4 7.5 9.1

7

9

Kaolinite 45 35 15 0 18 18 21-25

Illite 40 0 0 65 18 0 17-25

Clay mineral composition Feldspar Montmorillonite Interstratifies 15 65 85 35 64 82 10-11

Quartz 5

Calcite 10

MBA

Standard

0,2 Methylene blue test: NF P 94-068

25-39

13-21

TABLE 22 CLAY MINERAL COMPOSITION, METHYLENE BLUE ADSORPTION VALUE AND STANDARDS IN ANALYSED TESTS

Tests Nº

MO

pH

0,15 7,1

SO4 CO3

SiO2

Al2O3

Chemical composition Fe2O3 MgO CaO SO3

32,22

2,24

0,53

0,03

K2O

Na2O

Cl

31,8 5,81 0,15

0,03

0,005

Granitic Residual Soils constitued by silicates (in more than 65%) 0,59

TiO2 MnO FW* 0,2

0,02

26,9

Standard NF6 P 15-467 ASTM D 2488 UNE 41410

TABLE 23 CHEMICAL COMPOSITION AND STANDARDS IN ANALYSED TESTS

85

5.6.3. Chemical and mineral composition of earth: conclusions It can be said that swelling potential can be estimated by MB test accurately and easily without time consuming clay content and activity determining tests. [59] The first thing to say is that, generally, the mineralogical and chemical composition of the soil is not taken into account. This is a big mistake that cannot be ignored in the standardization process.

5.7. DENSITY AND MOISTURE CONTENT OF SAMPLES 5.7.1. Tests’ table Article Soil Nº

1

2

3

4

5

6

Batch/ Sample 1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.5 2.6 3.1 3.2 3.3 3.4

Dry density [kg/cm3]

Moisture content [%]

2,06 2,09 2,14

4,8 5,8 8,8 5,5 7,1 8,4 8,6 9,4 10,2 15,5 12,2 12,2 13,0 Optimum Moisture Content

2,017-2,061

1,5303 1,7006 1,7412 1,6251

4.1

1,877

5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 6.1 6.2 6.3

1,9718 1,9813 2,0054 1,7910 1,7581 1,9947 2,1528 1,9396 1,7931 2,0075

Optimum Moisture Content

Maximum Dry Density

Optimum Moisture Content

Maximum Optimum dry moisture Normative density content [kg/cm3] [%] 2,12

9,9

Modified Proctor

2,16

8

Vibrating hammer BS 1377

1,877

11,75

1,92 1,84 1,71

5,8 8,3 6,4 7,4 9,6 5,6 5,4 7,4 9,4 5,3 12 12 12

Modified Proctor

Standard Proctor

86

6.4 6.5

Just slightly lower than the maximum dry density

6.6 6.7

7.1

7.2

7 7.3

7.4

7.5 8

7.1.1 7.1.2 7.1.3 7.1.4 7.1.5 7.1.6 7.1.7 7.1.8 7.1.9 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7.2.7 7.3.1 7.3.2 7.3.3 7.3.4 7.3.5 7.3.6 7.3.7 7.3.8 7.3.9 7.3.10 7.3.11 7.3.12 7.4.1 7.4.2 7.4.3 7.4.4 7.4.5 7.4.6 7.4.7 7.5.1 7.5.2 7.5.3 7.5.4

Optimum Moisture Content considering the liquid phase of the additive 2 4 5 6 7 8 9 10 11 2,2 2,8 4,5 6 8,5 12 13,8 1,5 2,5 4 4,8 6 6,8 8 8,8 10,5 11 11,8 12,4 1,9 3,6 5,2 6,6 8 10,2 12,2 2,2 5 8 12 5,32

2,01

10

1,71

12

1,71

12

1,71

12

TABLE 24 DENSITY AND MOISTURE CONTENT IN THE ANALISED TESTS

87

5.7.2. Density of samples: conclusions The vibrating hammer test was used in test nº 2 in preference to the standard Proctor test as it better resembled the compaction effort in a real rammed earth wall. As said, the test methodology have to be alike the construction technique for which they are held, therefore, in normalization we must introduce an alternative for each test that deals with different but popular rammed earth building techniques. In this direction, the standard Proctor test is in general preferred to the modified Proctor for traditional rammed earth works, since the compaction energy of traditional rammed earth is closer to that of the first test. On a qualitative level the wetter samples have greater ductility whereas the drier samples are brittle. In test nº 7, the influence of moisture on the mechanical characteristics of rammed-earth material has been studied, on different soils (sandy, clayey, stabilised) and with great variation of moisture content: from the wet state directly after manufacturing (11-13%) to “dry” state in atmospheric conditions (1-2%). Samples in this study were manufactured and tested in unconfined compression at different moisture contents which correspond to different values of suction. In addition, the Poisson’s ratio was determined, it varied from about 0.2 for the “dry” samples to 0.37 for the wet samples. This coefficient can be used in modelling structures, in static or dynamic. The water sensitivity of the rammed-earth material and other earthen materials is a widely perceived weakness. However, this paper showed that a slight increase in moisture content of dry rammed-earth walls (moisture content not exceeding 4% by weight, e.g. due to rain fall or change of RH in the atmosphere did not accompany a sudden drop in the wall’s strength. Indeed, in this domain, the compressive strength was quasi-constant for sandy soil and stabilised soils and a decrease about 10% for the clayey soil. [44] But still, there is not enough data to state that the Optimum Moisture Content is the greatest value for testing rammed earth, although is the most extended procedure. Anyway, is very important to take in account the liquid phase of the additive (as shown in test nº 6.6 and 6.7). Jaquin et al. [39] studied the influence of suction on mechanical characteristics of rammed-earth material. This study found that suction was a source of strength in unstabilised rammed-earth, and that the strength increased as moisture content reduced. However, in that study, the moisture content only varied between 5.5% and 10.2% (by mass), while the moisture content of an unstabilised rammed-earth Wall in normal conditions is around 1-2%. In addition, in that study, only one soil was tested and the mechanical strengths obtained were relatively low (fc≈0.5 MPa) compared to current values 1-2 MPa.

88

5.8. COMPRESSIVE STRENGTH 5.8.1. Introduction The results in the tests should be compared to existing standards: Compressive strength [N/mm2] The Code ACI ASTM Enforcement NMAC New SNZ Materials, Standards International of Rammed 14.7.4 DIN Mexico HB 195 4298 Journal Australia E2392 / Earth USA 18954 Building Australia New Comitee (2002) E2392M – Structures of (New Germany Code Zealand (1990) 10e1 (2010) Zimbabwe Mexico) (2001) Sandy soils with pebbels Silty soils Clayey soils Unstabilized / Stabilized rammed earth

2.76-6.89

-

-

-

-

-

-

-

-

2.07-6.21 1.72-4.14

-

-

-

-

-

-

-

-

1-15

2.068

>1.5 (1 floor) >2 (2 floors) 400 mm thick walls

>2 1

>2.12

>1.33

3-5

>2.07

TABLE 25 COMPRESSIVE STRENGTH OF RAMMED EARTH IN SEVERAL INTERNATIONAL STANDARDS. ADAPTED FROM [40] [56]

1

Dry unconfined characteristic strength obtained from earth blocks or cylindrical earth specimens On cured rammed earth specimens. No information is provided on the preparation of the specimens 3 Lowest of 5 specimens with 1:1 height/thickness ratio 2

89

5.8.2. Tests’ table Tests Nº

1

2

3

Soil

1.1

Sample/Batch

Compressive Young’s strength [N/mm2] modulus Wet [N/mm2] Dry state state

1.1.1

1.39

1.1.2

2.45

1.1.3

2.94

2.1

2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.1.6

3.1

3.1.1 3.1.2 3.1.3 3.1.4

4.1

15,4

9

4.2

18,4

12,7

4.3

15,9

10,1

4.4

17,8

11,7

4.5

17,5

12,3

4.6

21,5

15,6

4.7

17,2

11,5

4.8

19,5

14

5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 6.1 6.2 6.3 6.4 6.5 6.6 6.7

0,3 0,56 0,34 0,42 0,54 4,56 8,3 3,88 2,6 0,3

Maximum strength with maximum Proctor density

These tests were carried out according to a test developed by l’Ecole Nationale des Travaux Publiques de l’Etat (ENTPE) [62] which was then adapted by the Normes Françaises [63]. In this study, two methods of curing were used: a humid atmosphere and a humid atmosphere plus immersion in water. We refer “Dry state” to the tests carried out to the samples cured with the first method of curing and “Wet state” for the second ones.

4

5

6

Average of three samples for each soil

Average of three samples for each soil

0,41 0,25 0,43 0,41 0,72 0,93 1,09

Strength test details

100 80,5 70,6 221,6

The tests were carried out under monotonic displacement control at a rate of 3 µm/s and the vertical deformation at the middle third of each specimen was measured by means of three LVDTs disposed radially.

90

7.1

7.2

7 7.3

7.4

7.5

7.1.1 7.1.2 7.1.3 7.1.4 7.1.5 7.1.6 7.1.7 7.1.8 7.1.9 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7.2.7 7.3.1 7.3.2 7.3.3 7.3.4 7.3.5 7.3.6 7.3.7 7.3.8 7.3.9 7.3.10 7.3.11 7.3.12 7.4.1 7.4.2 7.4.3 7.4.4 7.4.5 7.4.6 7.4.7 7.4.8 7.5.1 7.5.2 7.5.3 7.5.4

8

8.1

8.1.1 8.1.2 8.1.3 8.1.4 8.1.5 8.1.6 8.1.7 8.1.8

9

9.1

9.1

1,9 1,9 1,7 1,6 1,35 1,25 0,8 0,6 0,4 1 0,95 0,9 0,8 0,65 0,4 0,15 1,7 1,67 1,55 1,4 1,2 1,15 0,95 0,85 0,5 0,47 0,37 0,25 2 1,85 1,7 1,4 1 0,9 0,6 0,4 0,8 0,75 0,75 0,7 3,4 4 2,7 3,7 2 4,4 2,7 2,5

2.33 ~ 3.38

The values given are average results from 3 specimens. In addition, the article shows the results in graphics instead of tables, thus the values given are an eye approach from graphics. In this graphics, the average of three samples is given for each batch with a different moisture content tested. Thus, the graphics show the strength variation of the soils with the variation of moisture content. The more uneven upper Surface was capped with a mortar (2 lime: 3 sand by weight) to provide a flat smooth Surface. Some tests were under force control (3 KN/s) and others under displacement control, but results did not differ.

386,55 461,57 296,84 419,2 127,22 296,72 549,76 334,34

Before carrying out the compression tests, the samples were capped using high-strength self-levelling concrete by using a calibrated levelling table for supporting the samples, in order to guarantee a perfectly horizontal Surface. The compressive strength was analysed using Incotecnic MUTC200 equipment and

91

9.2

9.3

1.90 ~ 4.87 1.16 ~ 1.95

following the standard UNE-EN 196-1. For each type of soil, several samples were tested with different percentage of the components according to the mixtures given by an optimization process.

TABLE 26 COMPRESSIVE STRENGTH IN THE ANALYSED TESTS

5.8.3. Compressive strength: conclusions We must insist saying that there are not standards specially developed for testing Rammed Earth, which leads to the fact that each test analysed is different. Some of them put the samples in a controlled storage conditions and the tests are launched when the sample gets to the moisture content desired. We call this: “Wet state”. When the samples are introduced into the oven to fully remove water is named as “Dry state”. However, in test 7 “Wet state” means that the curing procedure ends with the samples submerged in water to saturate them meanwhile “Dry state” means what “Wet state” means in the other tests like explained before. Before carrying out the compression tests, the samples should be capped in order to guarantee a perfectly horizontal surface so that the compression force is applied as a uniformly distributed load over a consistent area of the sample. If there are irregularities on the simple Surface, the applied force could be concentrated through particular points of the sample which would affect the failure behaviour and possibly cause inaccuracies in the results. It can be done by different methods: capping using high-strength self-levelling concrete (test nº 8), using mortar (test nº 7) or using a plywood sheet or similar (v. Fig. 103). Some authors recommend one method or another ( [49], [64]). We think the last method is the best since it is the cheaper and easiest way to transfer the compressive strength smoothly. Moreover, each plywood can be used twice (each time for one side) and recycled after used. There has to be noticed that in test nº 7, at the beginning of each test, a preload corresponding to 0,02 MPa was applied to assure that entire upper face of sample was in contact with the press’s plateau. Other important fact is the formula used to give the final result. Almost any test explain this. Either they use a simple arithmetic average or they give the lowest value obtained as the final result. This procedure has to be normalized following the example of any concrete standard or similar. The recommendation to test the unstabilised compressed soil of rammed earth samples in fully dry (oven-dried) or in fully saturated (soaked in water) conditions seems questionable for unstabilised samples. The latter condition is impossible to implement, and the former might give significantly under-estimated values of strength. [42] The alkaline activation of fly ash resulted in a substantial increase in stiffness for all mixtures. The strength increase is also an evident result, since the compressive strength of the SRE specimens ranges between 1.7 and 2.5 times higher than that of the URE specimens. However, the strength improvement presented by the mixtures was not sufficient to exceed the required performance for rammed earth construction (Table 25). The obvious solution to achieve adequate strength would be the incorporation of higher fly ash contents, since several studies have shown that the higher the ash content, the higher is the strength [55]. However, it should be noted that the same referenced studies have concluded that a curing period of 28 days is not enough to allow the complete development of the geopolymeric matrix, responsible for the strength increase of these materials

92

Ongoing tests by the authors seem to show that the average compressive strength at 90 days can double the values obtained at 28 days, but further tests are required to evaluate this effect. [56] Compressive strength decreases with increasing moisture content that is logical. However, when moisture content is below 4% (close to air dry), the variation of compressive strength was not significant. [44] It is noted that the stabilization by hydraulic lime can decrease the sensibility to water of RE material but it does not always accompany an increase in compressive strength. In addition, specific curing of lime stabilised samples could give better results. [44] With cement stabilisation, great strength values can be reached. For example, at the University Politechnika Warszawska we obtained around 10 MPa for 8% cement (by weight) samples; that values are reached also in test nº 4 using cement plus resin. This is a great improvement for earth building, but still we should keep in mind that the use of cement is pushing us in the wrong direction of sustainable construction. Even so the use of stabilizers as fly ash or straw must be included in the future rammed earth standards as a preferred choice instead of the use of cement. In any case, stabilised rammed earth is good to introduce earth building in the cities since the buildings at cities have to be taller than in rural areas because the soil is very limited and valuable.

93

6. SIMPLE COMPRESSIVE TEST AT THE WIL The pictures below show the tests carried out at the Faculty of Civil Engineering in Warsaw (WIL), with one of the Piotr Narloch’s students groups. The experience was unforgettable since it was a great approach to the rammed earth simple compressive tests, which is the main subject of this work, so that we could implement all the knowledge acquired. The data of the tests are not included in this project as they belong to the polish student group and its part of a series of studies on rammed earth that will be used to draw the future Polish standards on this material. Professor Narloch has invited us to participate in this hard task and provide us the articles written on the basis of these experiments when they are published.

FIG. 83 TAKING OUT THE FIRST BATCH OF RAMMED EARTH SAMPLES FROM THE STORAGE CHAMBER AFTER 28 DAYS CURING PERIOD

94

FIG. 84 STORAGE CHAMBER WITH CONTROLLED MOISTURE AND TEMPERATURE

95

FIG. 85 SELECTION OF PLYWOOD TO REUSE THE ONES WITH ONE VIRGIN SIDE

FIG. 86 SANDING THE SURFACE TO MARK THE SPECIMENS WITH CHALK

96

FIG. 87 WEIGHING THE SPECIMENS

FIG. 88 MEASURING THE SAMPLES

97

FIG. 89 COMPUTER WITH SIMPLE COMPRESSIVE TEST SOFTWARE AND PRESS FOR TESTING SAMPLES

FIG. 90SAMPLES READY TO BE TESTED WITH THE PLYWOOD SHEET USED TO SMOOTH THE TOP SURFACE

98

FIG. 91 PROFESOR NARLOCH WRITING ANOTATIONS DURING THE EXPERIMENT

FIG. 92 ME WRITING ANOTATIONS DURING THE EXPERIMENT

99

FIG. 93 THE PRESS AND ONE SAMPLE WITH 9% CONTENT OF CEMENT READY TO BE TESTED

FIG. 94 CARRYING OUT THE TEST

100

FIG. 95 SOFTWARE

FIG. 96 INTRODUCING THE DATA OF ONE SAMPLE IN THE SOFTWARE

FIG. 97 SCREENSHOT OF ONE OF THE TESTS. STRENGTH VALUE: 12.57 MPA

101

FIG. 98 PUTTING ONE SAMPLE IN THE PRESS

FIG. 99 STARTING ONE TEST

102

FIG. 100 GARBAGE CAN FOR TESTED SPECIMENS

FIG. 101 ONE SAMPLE AFTER THE TEST

103

FIG. 102 TESTING

FIG. 103 DETAIL OF POSITION OF SAMPLES IN THE PRESS

104

FIG. 104 RESULTS GIVEN BY THE SOFTWARE AFTER THE TEST

105

7. BIBLIOGRAPHY [1]

Fermín Font, Pere Hidalgo, "Arquitecturas de Tapia", Castellón: Colegio Oficial de Aparejadores y Arquitectos Técnicos de Castellón (COAAT), 2009.

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