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Strength of Natural Soil Bricks


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Strength of Natural Soil Bricks

  1. 1. STRENGTHS OF NATURAL SOIL BRICKS By Dr-Ing. John K. Makunza University of Dar es Salaam Department of Structural Engineering 12th December 2006 1
  2. 2. 1.0 IntroductionAn adequate shelter is a basic human need, yet about 80%of the rural population in developing countries still live inspontaneous low quality settlements, as they cannot affordthe high cost of building materials which could producebetter shelters. One alternative for the expensive materialsis to use natural soil stabilized bricks because they havebeen identified as low cost material with the potential ofreducing the problem of living in poor or sub-standardhouses. The technology uses the available soil on site, whichis stabilized with a small amount of cement or/and limedepending on the characteristics of the soil so as to improvethe engineering properties of the produced bricks. 2
  3. 3. Problem StatementResidents of most areas of Southern Highlands in Tanzaniahave been using mud bricks and interwoven timber,saplings or bamboo daubed with mud to build their housesand sometimes they apply cement plaster on the walls.Problems of the houses:- vulnerable to weather especially during rain season- soil material can expand and loose cohesiveness, particularly with cement plaster- they are not sufficiently strong, although they somehow last long even for more than ten years.- it has been learnt that thieves can easily chop-out some bricks or part of the mud wall and break-in then steal properties.Therefore the houses are not safe and are less reliable.Examples of the houses are shown in Figures 1, 2 and 3. 3
  4. 4. Figure 1: Traditional house constructed of mud-walls and roofed with grass 4
  5. 5. Figure 2:House built of pure soil bricks (from non-stabilized soil) 5
  6. 6. Figure 3: Pure soil brick-wall in which part of the cement plaster has fallen away 6
  7. 7. 2.0 ObjectivesThe main objective of this study was to assess thesuitability of bricks made of stabilized soil, as towhether they can be used for the construction ofstrong, safe and reliable low cost houses, or otherwise. 7
  8. 8. 3.0 Adopted MethodologyThe methodology adopted in carrying out the studyincluded the following:• literature review: Through reading different books, journals, some publications, and information obtained about properties of soils and soil stabilization,• site visits and sample collection in which samples S1 and S2 were collected• laboratory tests and data analysis in which the samples were tested and the data obtained analyzed to check the characteristics and adequacy of the soils as well as the bricks. 8
  9. 9. 4.0 Soil StabilizationIn many developing countries especially in rural areas, soil is usedfor the construction of houses. Natural compacted soil has goodinsulation and fire resistant properties[1]. It is, however,vulnerable to moisture and the erosive effects of weather. Wallsconstructed out of well compacted soil, have adequatecompressive strength under dry conditions; however they willloose their strength under adverse moisture content. Soil durabilityand strength can also be improved by:(i) Changing the distribution of grain size; gradation control(ii) Compacting the soil;(iii) Adding stabilizers or chemicals;(iv) Mixing all of the above.Soil can be improved and used as a building material for varioustypes of structures by adding substances known as stabilizers,and the product is called stabilized soil. A properly stabilized,consolidated, well-graded soil that is adequately moisturized,mixed, and cured will provide a strong, stable, waterproof andlong-lasting building bricks. 9
  10. 10. Functions Stabilizers in SoilsStabilizer material in the soil will do the following;(i) cementing/binding the soil particles together making the product stronger(ii) water proofing - reducing the amount of voids and water which can be absorbed by the soil(iii) reducing the shrinkage and swelling properties of soil(iv) increase the tensile strength of soil.Some Commonly Used Stabilizers are;(i) cement(ii) lime(iii) combination of lime and cement(iv) combination of lime and Pozzolana(v) asphalt(vi) burning clay bricks*** 10
  11. 11. 5.0 Soil Tests and Results5.1 Bottle testThe aim of this test was to determine the approximate amount ofclay, silt, sand and gravel presence in the soils.Table 5.1 Summary of bottle test results Soil description S1 S2 Height of clay/silt content (mm) 250 220 Total height of the content (mm) 480 480 Percentage of clay/silt (%) 52.1 48.55.2 Atterberg limitsSoils can have various states of consistency, liquid, plastic or solid.The boundaries separating the limits and indices, are expressed aspercentages by weight of the moisture content.Table 5.2: Summary of Atterberg limit test Soil sample S1 S2 Liquid limit (wL) % 43 37.6 Plastic limit (wP)% 21 20 Plasticity index (IP)% 22 17.6 11
  12. 12. 5.3 Box (linear shrinkage) testThis test is used to determine the amount of cement or lime tobe used for stabilizing a particular soil. The test results for soilsamples S1 and S2 were as follows;Table 5.3: Summary of linear shrinkage test results Sample soil S1 S1 Shrinkage (mm) 12 185.4 Grain size distributionTable 5.4: Summary of particle size distribution Soil description S1 S2 Clay (%) 34 25 Silt (%) 23 23 Sand (%) 40 51.3 Gravel (%) 3 0.7 Solid density (kg/dm³) 2.65 2.65 Soil description Gravelly silty Gravelly silty clayey SAND clayey Sand 12
  13. 13. 6.0 Production of Bricks (a) (b) brick size: 300 x 114 x 145 mmFigure 4: (a) Hand steel mould, (b) Stabilized soil bricksMix Ratio: Cement: lime: soil 1:1:15 batch by volume cement: water 1:4 (water cement ratio) 13
  14. 14. 7.0 Testing of BricksCompressive Strength TestThis test was done in order to determine thecompressive strength of the bricks againstvertical loading. The procedure for testingeach brick was done as follows:à Externaldimensions of each sampled brick weretaken and the brick was marked foridentification• The brick was weighed and recorded ingrams• The brick was placed into the machineand all set-up procedures were properly Fig. 5: A Brick under testdone• The brick was gradually loaded until itfailed• The ultimate load was recorded. 14
  15. 15. Results – Sample S1 Densities of soil Bricks - S1 1.8 1.7 Desnity [g/cm³] 1.6 1.5 1.4 1.3 1.2 1.1 1 1 2 3 4 5 6 7 Sample No [] Figure 6: Densities of bricks – sample S1 15
  16. 16. Co m pre ssive stre n gth o f S oil Brick s - S 1 T e st Re sults BS 562 8 Va lue 6 5Stress [N/m m ²] 4 3 2 1 1 2 3 4 5 6 Sa m ple No Figure 7: Compressive strength for bricks from sample S1 16
  17. 17. Results - Sample S2 Densities of Soil Bricks - S2 2 1.8Density [g/cm³] 1.6 1.4 1.2 1 1 2 3 4 5 6 Sample No [] Figure 8: Densities of soil bricks from soil sample S1 17
  18. 18. Compressive strength of Soil Bricks - S2 Test results BS 5628 Value 6.00 5.00Stress [N/mm²] 4.00 3.00 2.00 1.00 0.00 1 2 3 4 5 6 Sample No [] Figure 9: Compressive strength for bricks from sample S2 18
  19. 19. Water absorption test resultsThe test was carried out in order to assess the waterabsorption of the bricks. Results: Average water absorption for bricks from sample S1 = 12.3% Average water absorption for bricks from sample S2 = 9.86% Specification control values : not greater than 20% 19
  20. 20. 8.0 Compressive Strength Test of Sample WallsLoad bearing wallsmay be designed tocarry in planehorizontal loadsinduced by wind,bracing effects orearthquake; theloads are transferredto the wallsprimarily viadiaphragms such asfloors or roofs. Figure 10: Wall specimen under test 20
  21. 21. Results:Average maximum load: 137.00 kNAverage compressive strength: 1.22 N/mm2From practical point of view, the strength ofwalls for normal residential buildings is less than0.60 N/mm2 21
  22. 22. Application of stabilized soil bricksFigure 11: Guard’s hut built from stabilized soil bricks 22
  23. 23. 9.0 Concluding Remarks• Basing on the results obtained in this study, it has been found that bricks made from stabilized soil with a mix ratio of 1:1:15 for cement: lime: soil have compressive strengths greater than that specified in the British Standard (BS 5628 Part 1) of 2.80 N/mm2.• It has also been learnt that this technology uses less amount of cement in the production of bricks when compared with cement sand blocks• Building with stabilized soil bricks is a technology which offers a good possibility for enabling low income groups to build their own houses at low cost• stabilized soil bricks have more advantage when compared to burnt bricks because they are environmentally friendly since there is no felling of trees for burning the bricks. 23
  24. 24. Burnt BricksFigure 12: Burnt brick site near Ifunda – Iringa region 24
  25. 25. Recommendations To achieve a successful dissemination of this technology, the following recommendations should be implemented.• Promoting stabilized soil bricks through advertising and pilot housing, so that many people could have much knowledge about this technology.• To prepare operation manual for the soil preparation, use of the bricks press and building process.• Training people about the production of these bricks.• Further research on use of stabilized soil bricks for low- rise buildings is required. In this case a study on the strength of walls against lateral loading and earthquake effects is deemed necessary. 25
  26. 26. Steel Mould for Bricks ProductionFigure 13: Steel mould for bricks production 26
  27. 27. Fig. 14:Map ofTanzania 27