Evaluation of Rice Husk Ash Stabilized Lateritic Soil as Sub-base in Road Construction

Laboratory experiments were conducted and the results were analyzed for rice husk ash (RHA) stabilization of laterite soils for utilization as sub base materials in road construction. The index properties classified the soils as (A-7) under the AASHTO soil classification scheme. The soils were stabilized with 2.5% increment between 5 - 12.5% of rice husk ash (RHA) by dry weight of soil. Performance of the soil-RHA was investigated with respect to compaction characteristics, California bearing ratio (CBR) and unconfined compressive strength (UCS) tests. Addition of RHA decreased the maximum dry density while it increased the optimum moisture content at 5% RHA; the values of maximum dry density (MDD) and optimum moisture content (OMC) were 1962 kg/m³ and 24% respectively. California Bearing Ratio results showed that the peak CBR (soaked) value was 135.5% (for 7.5% RHA stabilization) which indicates 92.44% increase over the CBR value obtained for the laterite soils in their natural form. The lowest CBR (soaked) value occurred at 12.5% RHA stabilization. The unconfined compressive strength test results showed that the strength for natural soil was 107.32N/mm² and the highest UCS value for the stabilized soil was 68.82% (the value obtained for 5% stabilization using RHA). This gives 40.5% decrease in the UCS of the natural soil. This research shows little potentials of using RHA only for soil improvement, it is recommended that 5% of RHA be added to soil samples for field stabilization for the purpose of improving the soil engineering properties of the laterite soil for pavement sub-base construction. To achieve high pozzolanic behavior, it is recommended that RHA intended for use in stabilization are calcined burnt between 600ºC and 700ºC temperature [1].