Investigating the Effects of Kaolin Mixed With Cement On Strength of Expansive Subgrade Soil

Abstract

Expansive soils have the tendency to behave volume change during wetting and drying scenario. This behavior of the soil cause large uplift pressure, differential settlement, and upheaval of structures built on them. Avoiding these types of unsuitable soils is mostly impractical, hence stabilization practices are considered to reduce the pre-specified behavior of the soils. The swell and shrinkage distinctiveness of expansive soil causes significant damage to structures such as buildings and pavements. The above problems are extensively occurring in Ethiopia. These clays are a consequence for expansive and unstable soil. As a result, they make pavement structure fail. The general objective of this research was to Investigate the effect of kaolin mixed with cement on strength of expansive subgrade soil. In this study Atterberg Limits Tests, Particle Size Distribution, soil Classification, Free Swell Index, linear Shrinkage, Specific Gravity, Compaction (Moisture density relationships) tests, CBR and CBR-swell was determined. The research design was followed the experimental type of study which begins by collecting samples. The sampling technique used for this research was a purposive sampling which is non– probability method. Two expansive soil samples were taken for the study by observation and free swell index tests at a depth of 1.50 m to remove organic matter. Kaolin was taken from Tabor ceramic factory, in which the factory uses the material from Bombowha kaolin deposit located in Southern Ethiopia, Borena Zone, Bore district, at the locality called Bombowha. Result of the chemical composition of kaolin shows that the total content of Silicon Dioxide (SiO2), Aluminum Oxide (Al2O3) and Iron Oxide (Fe2O3) was 83.58% and physical properties of kaolin was conducted on the fineness (residue on 45 microns), specific gravity, PI, OMC and MDD were 30,2.61,10.85%,27.25%, and 1.42g/cm 3 respectively. Both the chemical and physical properties were fulfilling the requirements according to ASTM C-618.Wuhafisash-Yetebaberut road soil sample has plastic index 68 %, free swell index 122 %, linear shrinkage 23.7%, and CBR value 0.98 %. Similarly, Bosa Addis Kebele soil sample has plastic index 56 %, free swell index 64 %, linear shrinkage 19.36%, and CBR value 2.02%. Since both the given soil samples were found with high degree of expansion, stabilization was made with mix-ratio of 10% kaolin and 10% cement alone, 2% kaolin + 8% cement, 4% kaolin + 6% cement,6 % kaolin + 4% cement, and 8% kaolin + 2% cement. The laboratory results obtained shows that 2% kaolin + 8% cement was an optimum ratio which achieved by most geotechnical parameters of the study. Moreover, Addition of 2%kaolin+8% cement yields almost the same result as addition of 10% cement content. Therefore, cement was partially replaced with 2% kaolin. All the laboratory result was compared with standard specifications. Since kaolin is not standalone stabilizer, it was recommended to study potential use of kaolin as admixture stabilizer. Additional curing time effect on all geotechnical laboratory tests should be performed. to have more accurate test results, additional test parameter like unconfined compressive strength, PH value test, volumetric shrinkage and mineralogical tests should also be performed