Compressed Earth Block Building Systems – An Experience In Undergraduate Research

 

 Joseph O. Arumala, Tariq Gondal, and Wa-Ki Bennett

Department of Technology

University of Maryland Eastern Shore

Princess Anne, Maryland

 

Some standard tests were conducted on local soils and the soils were used to make compressed earth blocks. The basic concept of this project was to explore the possibility of using local soils to make compressed earth blocks for the construction of residential buildings. This paper reports the results of a study done using two undergraduate students to study the properties of local soil materials and making compressed earth blocks with a block press that delivers a high compressive effort. The blocks were tested for dimensional stability, compressive strength and modulus of rupture. The compressed earth blocks made gave an average dry density of 108 pounds per cubic feet (pcf), an average modulus of rupture of 47.56 psi and an average compressive strength of 41 psi. at 16 days and 56.51 psi at 28 days.  A method of wall construction using the compressed earth blocks was demonstrated. The durability of the blocks when subjected to the rain and snow was also examined.

Key Words: compressed earth blocks, compressive strength, modulus of rupture, maximum density, optimum moisture content, block press, durability, total construction cost, wall construction 

Introduction 

The use of dried earth (adobe), as a building material dates back thousands of years. Some of the first structures inhabited by man were made of mud and clay. Dried earth construction remains common in some parts of the world where specific climate or economic conditions dictate, and where the earth construction (adobe) know-how is commonplace. Raw earth has been used for the construction of buildings since the most ancient times, and the traditional housing that exists in many parts of our planet bears witness to this fact. Abandoned and forgotten with the advent of industrial building materials, particularly concrete and steel, it is today the subject of renewed interest in developing countries as well as in industrialized countries. Often criticized for its sensitivity to water and its lack of durability, this building material has in its present form many advantages for the construction of durable, comfortable and low-cost housing. If logic and modern methods are applied to its use, it can be all of the following:

Today, earth building production techniques range from the most rudimentary, manual and craft-based to the most sophisticated, mechanized and industrial (Houben et al 1994). The compressed earth block is the modern descendent of the molded earth block, more commonly known as the adobe block. The idea of compacting earth to improve the quality and performance of molded earth blocks is however, far from new, and it was with wooden tamps that the first compressed earth blocks were produced. The turning point in the use of presses and in the way in which compressed earth blocks were used for building and architectural purposes came only with effect from 1952, following the invention of the famous little CINVA-RAM press. This was to be used throughout the world. With the 1970s and 1980s there appeared a new generation of manual, mechanical and motor-driven presses, leading to the emergence today of a genuine market for the production and application of the compressed earth block (Rigassi 1985, Guillaud, Odul, & Joffroy 1985). One of the major limitations of the manual machines is that they are slow and one is limited in how much force can be applied to the blocks. Adding a hydraulic ram to compress the soil and automated conveyors to deliver the blocks from the machine to the work area provides high level of production capacity and quality to the process. As many as 320 blocks per hour can be produced from these machines. Compressed soil blocks may have compression strengths of up to 1,400 pounds per square inch, suitable for load-bearing construction under the right conditions. The blocks from these machines are consistent in strength and dimension, as long as standard procedures are followed for quality control. The Advanced Earthen Construction Technologies (AECT) machines are good examples of quality mechanically operated machines (Graham & Burt 2001). 

Earth or soil is available universally. There is large variability in the properties of soils and soil investigations are performed for sites on which major construction projects are to be located. Standard methods are used to determine the densities of various soils and methods are available to determine the compacted strengths of soils used in construction works such as highways, runways and building projects. Based on the type of soil and its moisture content it is possible to determine the compactive effort that will produce a maximum density at optimum moisture content.  The basic concept of this project is to explore the possibility of using local soils to make compressed earth blocks with a block press for the construction of low cost residential buildings.  

Building codes have been developed for the use of compressed earth blocks in buildings. The New Zealand Standards (NZS 4297: 1998, NZS 4298: 1998, NZS 4299: 1998, NZS/AS 1530: 1998) for compressed earth construction give the details and specifications for building of compressed earth structures. Manuals and Guides for the construction of earthen structures have also been developed (Rigassi 1985, Guillaud, Odul, & Joffroy 1985). The compaction tests in this project were done according to ASTM D-698. In this project no plasticity tests were done. The thickness of the blocks is 4 inches. These blocks when built to specifications can be used as a safe alternative construction material.  

Houbain (1994) and Graham and Burt (2001) give examples of houses built with unrammed, rammed and compressed earth. Compressed earth blocks are safe alternatives to masonry. They are low cost and can be designed to be earthquake resistant (NZS 4297: 1998, NZS 4298: 1998, NZS 4299: 1998).  Compressed earth blocks are non-toxic, are sound resistant, fire-resistant, and insect-resistant (Vermeer Construction Company, 2001). Compressed earth blocks have excellent insulating properties - reducing heating and cooling costs. For a given soil sample, the optimum moisture/density ratio can be obtained through a standard Proctor test. From this test a range of moisture content at which the soil will give desired densities can be obtained. The compression strengths of the blocks depend on their densities. The compression strength of a soil can be increased by chemical stabilization.  Addition of between 5% - 10% of ordinary Portland Cement can enhance the properties of the blocks greatly. No cement stabilization was done in this testing program. This project was designed to give an opportunity to two undergraduate students to prepare locally available soils, make the building blocks with a block press and test for the engineering properties of the compressed earth blocks. The objective was to test local soils to see if they could be used for housing construction. This paper gives the results of testing the soils and making compressed earth blocks from them. The compressed earth blocks were tested for compressive strength and modulus of rupture. 

Obtaining Representative Field Samples 

Four samples were collected from various locations around the campus of the University of Maryland Eastern Shore, namely: 1. North side of timber truss bridge, 2. Near basket ball court at student hostel, 3. Agricultural land near parking lot on Back Bone Road, and 4. South-west corner of UMES water tower. Soil samples were free of objects such as trash, debris and organic matter. The grain particles were examined with a magnifying glass. The porosity and plasticity were checked by pouring water on a soil sample to see the rate at which it drains through the soil particles and by making wet soil ½ inch diameter ball by rolling between palms as well as rolling the ball into 1/8” diameter thread. In order to determine tentative percentages of sand, silt and clay of soil particles, the soil was subjected to the sedimentation test in which each sample was placed in a glass jar and the jar filled with water and stirred properly. The jar was kept in static condition for the settling of the soil particles. Each of the settled soil layer was measured with a scale rule and approximate percentages were obtained. Soils obtained from location # 4 were used in making the compressed blocks in this project. 

Tests on Soils 

The soils used for making the blocks were evaluated first by performing some tests for the purpose of classifying and identifying the types of soils. The tests performed were as follows: Sampling and Field Classification, Sedimentation Test , Soil Particle Size Test, Moisture Content Test, and Compaction Test. The students collected soil samples from the soil materials used for making the blocks and performed the above tests on them. Engineering properties of the soils were thus obtained. In the Particle Size (Sieving) Analysis, the soil was first passed through the #10 sieve. The material retained on this sieve was now passed through the stacks of sieves (3” - #10) in the sieve analysis. A portion of the material passing the #10 sieve was used for the hydrometer test. After the hydrometer test,  the material was thoroughly washed on a #200 sieve, oven dried and sieved through sieve numbers 10 through 200 ( fine sieve analysis). All the soil tests were done using a basic Laboratory Manual (McArthur, T. & Roberts, J., 1996).  

After classifying the soils, compressed earth blocks were made from the soils and the blocks were subjected to the following tests after the blocks have “cured” for several days.

Making The Compressed Earth Blocks 

HBP 520 Block Press 

The compressed earth blocks were made using the HBP 520 Block Press manufactured by Vermeer Manufacturing Company. The HBP 520 is shown in Figure 1. The HBP 520 Block Press according to documents produced by Vermeer Manufacturing Company has the following features:

 Figure 1 HBP 520 Block Press

The soil was obtained and mixed in preparation for making the blocks. Figure 2 shows the students preparing the soil. When the soil was ready it was fed into the hopper of the block press (see Figure 3) and the block making process started. Soil samples were also taken for the soil tests. The machine when started makes the blocks, and pushes them out in a continuous stream. Figure 4 shows the blocks being made. Some manufactured compressed earth blocks are shown in Figure 5. 

Figure 2 Students Preparing Soil For The Blocks       Figure 3 Soil Being Fed to the Hopper of the Block Press

Figure 4 The Compressed Earth Blocks             Figure 5 Some Compressed Earth Blocks 

The compressed blocks were weighed at regular intervals and the dimensions: length, width and height were also measured. At different days after manufacture, compression and modulus of rupture tests were performed on the blocks. 

Testing Compressed Earth Blocks 

Compression Test 

In this test, the blocks were tested for their compressive strength. The set up for the test is shown in Figure 6.

 Figure 6 Compression Test Set Up

Modulus Of Rupture Test 

The modulus of rupture test set up is shown in Figure 7.

 Figure 7 Modulus of Rupture Test Set Up

Compressed Earth Wall Construction

 The blocks after they have been properly cured for a minimum of 28 days, can be used to build walls as shown in Figures 8. 

 Figure 8 Compressed Earth Wall Construction in Progress 

Results

Some of the results of this project are shown in the following tables. 

Table 1 Quantities Of Soil Used In The Particle Grading Analysis

 Table 2 Results Of The Sieve Analysis

Table 3 Results Of The Fine Sieve Analysis

 Table 4 Compression Test for Compressed Earth Blocks

 Table 5 Moisture Content Test 

Table 6 Compaction Test

 Tables 1 to 3 give the results of the particle sieve analysis including the hydrometer and the fine sieve analysis. Table 2 shows that all the soil particles were finer than ¾” and soil Sample 4 had up to 58% of particles finer than sieve #10 (0.0787 inch). Table 4 shows the result of the compression tests on the 24 compressed earth blocks. The average compression strength is 50.43 pounds per square inch. Table 5 gives the results of the moisture content test performed on the first three samples. Sample 2 had the lowest moisture content of 9.95% and sample 3 had the highest moisture content of 17.93%. Table 6 shows the results of the compaction test for sample 4 and it indicates that the optimum dry density is about 118 pounds per cubic feet and the optimum moisture content is about 14%. Table 7 gives the results of the modulus of rupture (MOR) test and shows that the average value of the MOR for the blocks to be 43.54 pounds per square inch.

 Average Moisture Content and Densities of Earth Blocks 

Soil taken from NW side Water Reservoir UMES Princess Anne, MD

Average Moisture Content (mc) = 9.57%; Average Density = 108.85 pcf

Soil taken from NW side Water Reservoir UMES Princess Anne, MD

Average Density =119.03 pounds per cubic feet. 

Table 7 Modulus of Rupture   

Discussion of Test Results 

The field classification of the soils taken from depths of 10 inches to 24 inches shows that soils tested contained  a range of soil particles from 15% - 90% clay, 10% - 45% sand, 70% silt, 5% gravel and 10%  peat. The porosity and the plasticity ranged from medium to high. The sieve analysis shows that over 90% of the soil particles were finer than 3/8 inch sieve size. In the compaction test the optimum dry density is about 118 pounds per cubic feet and optimum moisture content was 14%. 24 blocks of three different sizes were made and cured in natural air duly covered with plastic sheeting to prevent rapid reduction of moisture content. Every block was labeled and measured, to calculate the volume. The tests performed on the soil samples showed the main soil constituents to be:  

The proportions of various kinds of material in the types of soils which are recommended for the manufacture of compressed earth blocks (Houben, Rigassi, & Garnier 1994) are:

Comparing the results to these guidelines, it can be seen that the local soil is deficient in the clay and silt proportions. Although it is understood that these guidelines are rarely enough for soil selection purposes, knowing these proportions is an important indicator of the suitability of soils for compressed earth blocks manufacture (Houben, Rigassi, & Garnier 1994).  

The compressed earth blocks made with such soil gave an average dry density of 108 pounds per cubic feet (pcf), and an average compressive strength of 50 psi. The average modulus of rupture of the blocks was 43 psi. These values are low. Building codes like the Uniform Building Code, and the New Mexico Adobe Rammed Earth Building Code, require average block compressive strengths of 300 pounds per square inch and an average modulus of rupture of 50 pounds per square inch for compressed earth block one story buildings. These local soils fail to meet such code requirements. 

One of the claims made by compressed earth equipment manufacturers is that the use of on-site soils (local soils on a given site) to make the compressed earth blocks eliminates material transport and reduces material handling and labor costs. This may not be possible in many instances as this project shows. If on-site soils are to be used under these circumstances extensive blending of different soil sizes some of which may be imported from other places and some form of chemical stabilization (addition of cement or lime) will have to be done. While these activities may be possible, they will introduce additional cost to the total cost of construction where introduced. 

Durability 

The partial wall shown in Figure 8 was built in the summer and left in a place where it was not completely protected from wind driven rain and snow. In the winter after the wall has been exposed to moderate rain and snow, it was observed that the blocks at the bottom were crushed due to the wetting and thawing of the blocks, see Figures 9 & 10. This sensitivity to water and lack of durability in its untreated form highlights the main reservation on the wide use of compressed earth as building material. The wall surface must be protected by the application of rain resisting “plaster” to prevent this type of deterioration. 

Figure 9 Crushing of Bottom Blocks After Exposure      Figure 10 Crushing of Bottom Blocks After Exposure

to Snow and Rain                                                                 to Snow and Rain (after 3 months) 

Possible Extensions of The Project 

It is proposed that in order to simplify the initial evaluation of  the types of soils available, series of tests as carried out in this project be performed on different types of soils with a view of seeking a correlation between different types of soils and the compression strengths of the compressed earth blocks made from them. This will help in the initial evaluation of the suitability of the soils for the type of houses to be built. The results of such tests may also be evaluated to see if there are other parameters that may assist in assessing the quality and strength of the compressed blocks made from available soils. The aim here is to come up with a simple method for determining the qualities of compressed earth made from different soils. It is also proposed to add different percentages of agricultural fibers and other elements like Portland cement to the soils and to see what extent the strength of the blocks will be enhanced. To keep costs down, additives should be easily acquired at low cost. 

Conclusion 

This research project was based on evaluating local soils to determine their suitability for making compressed earth blocks for use in residential buildings. The local soil constituent proportions were compared to recommended guideline proportions and found to be deficient in the silt and clay fractions 

The compressed earth blocks made gave an average dry density of 108 pounds per cubic feet (pcf), and an average compressive strength of 50 psi. and a modulus of rupture (MOR) of 43 psi. These are low compared to recommended values of 300 psi for compressive strength and 50 psi for modulus of rupture.  

The project has demonstrated that compressed earth blocks made from on-site soils may not be suitable for code-complaint structures. It may require some major intervention in the form of importation of soils from other places and chemical stabilization with Portland cement or lime to upgrade them to the point were blocks made from them will meet desired objectives. When this becomes necessary, additional costs of bringing the soil to desired specification will push up the total cost of construction of buildings made of compressed earth blocks. The importance of this is that inexpensive and sound houses will become less affordable.

Acknowledgements 

The authors are grateful to Vermeer Manufacturing Company which provided the HBP 520 Block Press that was used for making the compressed earth blocks and the University of Maryland Eastern Shore Minority Science and Engineering Improvement Program that provided funds for this project. 

References 

Schroeder W.L.  & Dickinson S.E., (1996) Soils in Construction, Prentice Hall, Inc., fourth edition. 

McArthur T. & Roberts J., (1996). Understanding Soil Mechanics Lab Manual, Delmar Publishers. 

Vermeer Manufacturing Company (2001), Case Studies, Vermeer Manufacturing Company, Pella, Iowa USA. 

Vermeer Manufacturing Company (2001), Earth Construction, Vermeer Manufacturing Company, Pella, Iowa USA. 

NZS 4297:1998 Engineering Design of Earth Buildings (1998) New Zealand Standards 

NZS 4298:1998 Materials and Workmanship for Earth Buildings, (1998) New Zealand Standards 

NZS 4299:1998 Earth Buildings Not Requiring Specific Design (1998), New Zealand Standards 

Rigassi, V., (1985) Compressed Earth Blocks: Manual of Production, Volume 1. Manual of Production, Deutsches Zentrum fur Entwicklungstechnologien – GATE in: Deutsche Gesellschaft fur Tecchnische Zusammenarbeit (GTZ) GmbH in coordination with BASIN.[WWW document]. URL www.gtz.de/basin/publications/books/cebvol1.pdf 

Guillard, H., Joffroy, T., Odul, P., (1985) Compressed Earth Blocks: Manual of Production, Volume 2. Manual of Design and Construction, Deutsches Zentrum fur Entwicklungstechnologien – GATE in: Deutsche Gesellschaft fur Tecchnische Zusammenarbeit (GTZ) GmbH in coordination with BASIN[WWW document]. URL www.gtz.de/basin/publications/books/cebvol2.pdf 

Nelson, W., (1976), Compressed Earth Blocks [WWW document]. URL www.networkearth.org/naturalbuilding/ceb.html 

Uniform Building Code (1997) Structural Engineering Design Provisions 

ASTM D698 Standard Compaction Test 

New Mexico Adobe and Rammed Earth Building Code [WWW document]. URL www.earthbuilding.com/nm-adobe-code.html 

Boulder, Colorado’s Alternative Building Materials Code [WWW document]. URLhttp://www.azstarnet.com/~dcat/Boulder.html Chapter 97, Earth Masonry Units 

Minke, Gernot, (2000) Earth Construction Handbook, Southampton, U.K.: WIT Press. 

Graham, Charles W. & Burt, Richard (2001), Soil Block Home Construction, BTEC Sustainable Buildings III Conference, Santa Fe, New Mexico. 

Houben, H., Rigassi, V., & Garnier, P. (1994), Compressed Earth Blocks Production Equipment, CDI and CRATerre-EAG, Brussels.