Stabilization of Expansive Clay Soil Using Bagasse Ash and Lime

Abstract

Expansive clay soil is encountered in most parts of Bungoma County and the preliminary investigation shows that it belongs to A-7-5 class of soil in the AASHTO soil classification system and generally has poor engineering properties. Traditional stabilizers like cement, lime and others have been efficient and effective in soil stabilization but their rising cost and negative impact to the environment has led to research into bagasse ash waste to be used as an alternative in soil stabilization. The study investigated the properties of expansive clay soil when stabilized by lime, bagasse ash and combination of lime and ash. The research covered grading test, Plasticity Index (PI) and California Bearing Ratio (CBR). First, particles size distribution was determined from grading test, secondly varying percentages (4%, 5%, and 6%) of lime was used to stabilize clay soil and then PI and CBR were determined. The same procedure was repeated for bagasse ash and finally the varying mix ratios of lime and ash 1:4, 2:3, 3:2 and 4:1 on the sample. The PI results were as follows; lime (26%, 21% and 14%), ash (34%, 33% and 30%) and ratio of lime/ash (32%, 29%, 24% and 20%) respectively. The trend indicated that the PI of the stabilized clay soil decreased with increase in the quantity of lime, ash and ratio lime to ash in all the samples. The addition of lime or bagasse ash also reduced the shrinkage and swelling factor of soil. The CBR was carried out using Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) from graph of dry density against moisture content obtained from proctor test. The CBR results were as follows; lime (38%, 45%, and 50%), ash (6%, 4% and 2%), and ratio of lime/ash (19%, 27%, 30%, and 36%) respectively. The trend indicated that California Bearing Ratio increased with increase in lime quantity added but decreased when bagasse ash was used. The combination of lime and ash gave good results that meet the set standard by road design manual part III of minimum CBR of 20 for sub base road. The results of ash on PI and low CBR values it was concluded that sugarcane bagasse ash alone cannot be used to stabilize expansive clay soil. It was found that both lime and bagasse ash reduced the linear shrinkage, however, the addition of lime reduced the linear shrinkage to a greater degree than the same percentage of bagasse ash. When lime and bagasse ash are combined at the optimum ratio of 4:1, the stabilization results of California Bearing Ratio of 36, plasticity index 20, Linear shrinkage of 9.0, negligible swelling create a material that can used for construction works. Therefore, this study shows that lime in combination with bagasse ash can be effectively used to improve expansive soils with low soaked CBR value and high plasticity. It’s therefore recommended that since bagasse ash can partially replaces lime in clay stabilization to form material with cementitious properties, the use of lime should be minimized to reduce creation of carbon dioxide.