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
xiv
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.