Acta Polytechnica CTU Proceedings doi:10.14311/APP.2018.15.0063 Acta Polytechnica CTU Proceedings 15:63–68, 2018 © Czech Technical University in Prague, 2018 available online at http://ojs.cvut.cz/ojs/index.php/app MODULUS OF ELASCITY OF UNFIRED RAMMED EARTH Barbora Mužíková∗, Tereza Plaček Otcovská, Pavel Padevět Czech Technical University in Prague, Faculty of Civil Engineering, Thakurova 7, 166 29 Prague 6, Czech Republic ∗ corresponding author: barbora.muzikova@fsv.cvut.cz Abstract. The article is focused on measurement and evaluation of elastic modulus of unfired rammed earth and determination of stress-strain curve in compressive test. Sets of different containt of clay, sand and water were made and their properties were evalueted and compared. It was found out that for the hightest elascity modulus is ideal the ratio of sand and clay around 75/25 up to 80/20, the sets with montmorillonite clay had substantialy smaller value of elascity modulusthan the sets with illite-kaolinite clay and the ideal content of water for sand/clay ratio 75/25 is around 0.295. Keywords: Rammed earth, elastic modulus, mechanical properties, stress-strain curve. 1. Introduction Nowadays utilization of the unfired earth as a building material is rising. The reason of the trend is mainly the fact that unfired earth is according to the princi- ples of sustainable building development. It is environ- mentally friendly thanks to using of the final product, there is no need to produce any intermediate products. More over unfired earth building is a hundred per-cent recyclable. On the other hand, the mechanical behav- ior of the material is not described enough to use the data for designing in practical engineering. This was caused by the leaving the rammed earth as a building material in the time when the characteristics of other materials started to be investigated. Due to this fact, there are no standards for design- ing such constructions. That is why the only way how to build such buildings is to have some expe- rience with the material and use gain knowledge in other constructions. Nowaday few researches start to pay attention (for example [1–4]) on the topic of un- fired earth. Worldwide there is only a few companies that are capable to build unfired earth house with all requirements of modern living comfort. One of these constructions is a visitor centre in southwest Wyoming (Fig. 1). It is built of 2500 m3 rammed earth. The energy is gained from the renew- able sources - photovoltaic cells, five wind turbines and geothermal system unsuring the heating and cool- ing of the building. Onother example can be a family house in New Mexico (Fig. 2). There are two big monolithic walls made of rammed earth. Over 150 tuns of material were used to build these two walls. The color of layer take turns to look like a rock cliff. There are also very old examples of rammed earth construction (such as The Great Wall in Chine, Mayen pyramid in Mexico) and even brand new construction are built. There is a map of unfired earth construc- tions worlwide in the Fig. 3. The orange color are areas where the unfired earth is a traditional build- ing material. The white marks are the unfired earth constructions that are stated in the UNESCO list. As you can see from the Fig. 3 unfired rammed earth is used in different climatic zone in the wold [5–10]. Figure 1. The tourist centre in Wyoming is built of rammed earth [11]. Figure 2. The family house in New Mexico [12]. 1.1. Properties of the material As it was written above rammed earth brings some advantages and of course even disadvantages compared to commonly used building materials such as concrete and steel. 63 http://dx.doi.org/10.14311/APP.2018.15.0063 http://ojs.cvut.cz/ojs/index.php/app B. Mužíková, T. Plaček Otcovská, P. Padevět Acta Polytechnica CTU Proceedings Figure 3. The orange areas are the places where unfired earth is a typical building material and white ones are stated in the UNESCO list [10]. First of all, lets take a look at the advantages. The material is according to the principles of sustainable development, there are no intermediate products - it is direct use of the final product, the building material (in case that there are no stabilisation such as lime or cement) is a hundred procenr recycable and it is a local material. These were the advanteges in the respect of ecology. Another properity of unfired earth is that it is able to balances air humidity in rooms. The loam in unfired earth walls is able to absorbe and desorb humidity faster and greater extent than any other materials. From this results keeping very healty living condition with reduced humidity in summer and elevated humidity in winter. The wall of rammed earth (as other heavy materials) stores heat. It can balance indoor climate in areas with hight diurnal temperature differences [13]. Another advantages is absorbing pollutants, cleaning the indoor air and shielding high frequency light. We can not forget to mention the fire resistant of unfired earth. The biggest development of massive unfired earth houses building was at the area of the Czech Republic in the beginning of 17th century. It was caused by big fires that destroyd wooden houses. Even so called "Fire patent" was published by Marie Terezie. It was ordering to have brick kitchen and chimney - built from unfired bricks [9]. More over earth material preservs timber and other organic materials and it is ideal to do-it-yourself constuction - in this case it is inexpensive. On the other hand there are also disadvanteges of the material. From the authors‘ point of view, the main one is a prejudice, skepticism and lack of trust- worthy informations about unfired earth worldwive - among laymen and even among civil engineers. This is conected to the fact that unfired earth is not a standardises building material. Next the material is not water resistant. It must by shetltered against rain and frost, especialy in its wet state. The sheltering can be done by roof overhangs, dampproof courses or appropriate surface coatings [14]. Another diad- vantage is shringing of the material during its drying [7, 15, 16]. 2. Composition of Rammed Earth The material that we need for creating rammed earth construction is a loam. Loam is a product of erosion from rock. The composition and varying properties of loam depend on local conditions. Loam is a mixture of clay, silt and sand and sometimes contains larger aggregates like gravel and stones. The particles can be sorted according to diameter: particles with di- ameters smaller than 0.002 mm are called clay, those between 0.002 and 0.06 mm are called silt, and those between 0.060 and 2.000 mm are called sand. Parti- cles of larger diameter are termed gravels and stones. Like cement in concrete, clay function is to binde all larger particles in the loam. Other larger parts - silt, sand and aggregates constitute the fillers in the loam. Depending on which of the three components is dominant, we can differentiate clayey, silty or sandy loam. Figure 4. The process of building a rammed earth wall. 64 vol. 15/2018 Modulus of Elascity of Unfired Rammed Earth Set Sand/Clay Ratio Water-Clay Ratio Pcs of specimens Bulk density Type of clay [-] [%/%] [-] [-] [kg/m3] [-] GEM I 80/20 0.370 4 2073 montmorillionite GEM II 75/25 0.370 6 2040 montmorillionite GEM III 75/25 0.295 6 1929 montmorillionite KR II 75/25 0.370 11 2134 illite-kaolinite KR III 80/20 0.400 12 2138 illite-kaolinite S III 75/25 0.295 4 2170 illite-kaolinite S IV 85/15 0.370 6 2036 illite-kaolinite S V 75/25 0.335 6 2179 illite-kaolinite Table 1. Composition of used mixtures. 2.1. Clay The clay is a product of erosion of feldspar and other minerals. The basic types of clay are known based on the way of creation. These are kaolinite, illite and montmorillionite. They differ in the lamellar structure. The clay changes the properities of the final product - mechaical properties and even the colour is different as can be seen in the Fig. 5. 2.2. Sand Sand and gravel are used as fillers. They are described by the graph of grain size distribution. 2.3. Water Water activates the binding forces of the clay. The amount of mixing water has influence on the properi- ties of the final product. Figure 5. Different type of used clay in specimens. 3. Production of Specimens The material for building specimens is loam and mix- ing water. That means it is a mixture of sand, clay and water. The loam is made in the laboratory, that means the chosen type of clay and sand (of known grain size distribution) are mixed together to cre- ate loam of exactly known composition to compare changes in composition with changes of mechanical properties of the final product. The amount of mixing water is determined depending on the amount of clay, and it is expressed by the water-clay ratio. The process of building rammed earth wall is as follows. First of all, the framework is built, then the first layer of rammed earth is filled in. Secondly the layer of moist earth is compressed by a tamper. Then next layers of moist earth are added and compressed up to the top of framework. Finally, the framework is removed and the result is a hard monolithic wall. The principle is shown in Fig. 4. Eight different prescriptions were tested for deter- mining modulus of elasticity E. Sets GEM with mont- morillonite clay and sets S and KR with illite-kaolinite clay, sets differed in the ratio of sand and clay and in the water-clay ratio. The composition of the prescrip- tion is described in Table 1. There are names of sets in the first column, then sand/clay ratio, water/clay ratio, the pieces of used specimen is in the forth col- umn, average bulk density of specimens and type of used clay in the last one column. Figure 6. Testing of specimens: compressive test. The laboratory produce of specimens is similar to the building of real constructions. Firstly the prescrip- tion is defined as a ratio between sand (the filler) and clay (the binder) and the water-clay ratio is deter- mined. Secondly the compounds were mechanically mixed together, then the moist earth en mixture was 65 B. Mužíková, T. Plaček Otcovská, P. Padevět Acta Polytechnica CTU Proceedings Set S/C - w Type of Clay fc ft E [-] [-] [-] [MPa] [MPa] [MPa] GEM I 80/20 - 0.370 montmorillionite 1.274 ± 0.157 0.072 ± 0.008 43.293 ± 6.865 GEM II 75/25 - 0.370 montmorillionite 1.211 ± 0.173 0.075 ± 0.007 33.548 ± 7.460 GEM III 75/25 - 0.295 montmorillionite 1.466 ± 0.433 0.045 ± 0.005 33.528 ± 7.442 KR II 75/25 - 0.370 illite-kaolinite 1.150 ± 0.096 - 54.584 ± 16.856 KR III 80/20 - 0.400 illite-kaolinite 1.077 ± 0.104 - 61.039 ± 22.202 S III 75/25 - 0.295 illite-kaolinite 2.017 ± 0.029 0.143 ± 0.009 99.176 ± 12.200 S IV 85/15 - 0.370 illite-kaolinite 5.890 ± 0.067 0.073 ± 0.005 37.356 ± 17.075 S V 75/25 - 0.335 illite-kaolinite 2.165 ± 0.037 0.127 ± 0.008 74.339 ± 19.428 Table 2. Measured modulus of elascity E. layer by layer pressed in to the mould by the drill or manually by a steel block. The specimens were re- moved from the mould and set in to the climatic cham- ber where the stable conditions were settled. Com- pressive tests (specimens of size 20×20×100 mm) were made after a month after the produce. The pictures from the testing are shown in the Fig. 6 and 7 . Figure 7. Compresive strenght test with extesometer that records displacements δ on the specimens (range 25 mm). Figure 8. Principle of determinig of modulus of elascity from σ-ε curve. 4. Method of Determining E Test for determining the static modulus of elastic- ity was the compresive strenght test. The load- displacement curve data were recorded during the test. From these data the stress-strain curve was calculated and then the modulus of elasticity was evalueted. The static modulus of elasticity (so called Young‘s modulus) E is a material property, that de- scribes stiffness. Mechanical deformation puts energy into a material. The energy is stored elastically or dissipated plastically. The way a material stores the energy is summarized in stress-strain curve (σ-ε curve) that can be determined from load-displacement curve (F-δ curve). Stress is defined as force per unit area and strain as elongation per unit length. Graphically the modulus of elasticity can be defined as a slope of the linear portion of the stress-strain curve. The modulus of elasticity is defined by the Hooke‘s law, this law says that for elastically deformation the stress σ is directly proportional to strain ε: σ = E · ε. (1) The stress-strain curve for GEM I set is show in the Fig. 8. It can be seen that the elasticity modulus can be determined as: E = ∆σ ÷ ∆ε. (2) The material behaviour is linear elastic, the stress- strain curve in the loading part has a shape of linear curve from the beginning to 0.8fc. Due to the fact it was supposed that tangent modulus and secant modulus are of the same value. 5. Results from the Measurements The arithmetic mean and the standard deviation for each set were settled from the measured values, they are in Table 2. There are the compositions of the sets, their compressive and tensile bending stregths ( ± standard deviation) [17–19] and the evalueted 66 vol. 15/2018 Modulus of Elascity of Unfired Rammed Earth Figure 9. Prescription of used recepises in triangle diagram. Figure 10. Comparing values of elascity modulus for all sets. elascity modulus ( ± standard deviation). Fig. 10 compares modulus of elascity of each set in a chart where the values are in MPa. The recepis are shown in the triangular diagram (Fig. 9) where three components of the mixture (sand, clay and water) are expresed by percent and are on the axis of the diagrame. The composition and the difference between the prescription can bee senn from the diagram. 5.1. Impact of Sand and Clay Content The set S IV had the minimum content of clay and water and maximum content of sand (85/15 - 0.370). Let us remember that the amount of water is settle by the water-clay ratio that means the less clay is used the less water is with same water-clay ratio. The clay that was used was the illite-kaollinite clay. This set reached the minimum value of illite-kaolinite clay sets 37.356 ± 17.075 MPa. Sets GEM II and KR II contained the maximum of water and minimum of sand, the ratio is the same at both sets (75/25 - 0.370). They differed in used clay. Illite-kaolinite clay was used at KR II and montmo- rillonite at GEM II. The set GEM II and GEM III reached the minimum value of all sets 33.548 ± 7.460 and 33.528 ± 7.442 MPa and the set KR II reached the second minimum value 54.584 ± 16.856 MPa of sets with illite-kaolinite clay. As a result it seems that the ideal ratio of sand and clay is around 75/25 up to 80/20. 5.2. Impact of Type of Used Clay Two types of clay were used - illite-kaolinite and mont- morillonite clay. Take a look to already mentioned sets GEM II and KR II. The ratio of clay, sand and water was the same (75/25 - 0.370), but the elascity modulus of KR II with illite-kaolinite clay is 1.6 times higher. Another sets GEM III and S III had the same ratio of clay, sand and water (75/25 - 0.295) and again they differed in type of clay. Illite-kaolinite clay was used at S III and montmorillonite at GEM III. The elascity modulus of S III with illite-kaolinite clay is nearly 3 times higher. The sets with montmorillonite clay had substantialy smaller value of elascity modulus so the type of used clay in loam is very important for the mechanical properies of the final product. 5.3. Impact of Water Content The set S III, S IV and KR II had the same ratio of sand and clay - 75/25. The differed in amount of mixture water - 0.295, 0.335 and 0.375. The values of E were 99.176 ± 12.202 MPa, 37.356 ± 17.075 MPa and 54.584 ± 16.856 MPa. So evidently, the optimal value of water-clay ratio is around 0.295 for sand/clay ratio 75/25. 6. Conclusions Sufficient data of rammed earth properties in relation to its composition have to be find out for extension of these constructions. The article was focused on eval- ueting elascity modulus of different sets of rammed 67 B. Mužíková, T. Plaček Otcovská, P. Padevět Acta Polytechnica CTU Proceedings earth. The main data that were found about depen- dence elascity modulus and composition of clay, sand and mixing water: • the ideal ratio of sand and clay is around 75/25 up to 80/20, • the sets with montmorillonite clay had substantialy smaller value of elascity modulusthan the sets with illite-kaolinite clay, • the ideal content of water for sand/clay ratio 75/25 is around 0.295. List of symbols E Elascity modulus [MPa] F Load force [kN] fc Comressive strength [kPa] ft Tensile bending strength [kPa] δ Displacement [mm] ε Strain [–] % Bulk density [kg m−3] σ Stress [kPa] GEM Sets with montmorillionite clay S Sets with illite-kaolinite clay KR Sets with illite-kaolinite clay Acknowledgements The research was financial supported by the Czech Sci- ence Foundation (GACR No.18-0884S) and by the Fac- ulty of Civil Engineering at CTU in Prague (SGS project No.16/201OHK1/3T/11). References [1] H. Araki, J. Koseki, T. Sato. Tensile strength of compacted rammed earth materials. Soils and Foundation (56(2)):189–204, 2016. [2] L. Miccoli, D. V. Oliveira, R. A. Silva, U. Muller. Static behaviour of rammed earth: experimental testing and finite element modelling. Materials and Structures (48(10)):43–56, 2015. [3] Q. Liu, T. L. Tong. Engineering properties of unstabilized rammed earth with different clay contents. 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Modern Methods of Experimental and Computational Investigations in Area of Constructions pp. 31–34, 2016. 68 http://craterre.org http://sirewall.com/ http://www.pagethink.com/v/blog-detail/Rammed-Earth-Construction-is-Cool-Again-and-Hot-/47/ http://www.pagethink.com/v/blog-detail/Rammed-Earth-Construction-is-Cool-Again-and-Hot-/47/ http://www.pagethink.com/v/blog-detail/Rammed-Earth-Construction-is-Cool-Again-and-Hot-/47/ Acta Polytechnica CTU Proceedings 15:63–68, 2018 1 Introduction 1.1 Properties of the material 2 Composition of Rammed Earth 2.1 Clay 2.2 Sand 2.3 Water 3 Production of Specimens 4 Method of Determining E 5 Results from the Measurements 5.1 Impact of Sand and Clay Content 5.2 Impact of Type of Used Clay 5.3 Impact of Water Content 6 Conclusions List of symbols Acknowledgements References