A Study on improvement of unsuitable soils for road construction using lime and fly ash

In Sri Lanka, residual soils are abundantly encountered in constructions where residual soils with poor engineering properties have been left unused in many situations. However, it is uneconomical and non-ecological to leave these soils unused. As a solution, stabilizing the soils with chemical techniques such as lime and fly ash stabilization to the required properties has become popular and sustainable. In this study, an unsuitable residual soil was stabilized with 3%, 5% and 8% of lime, 6%, 12% and 18% of fly ash and with 3% lime increasing the fly ash percentage at 6%, 12% and 18% by dry soil mass to investigate the variation in soil properties to be used in road constructions. First, the basic soil properties were investigated. Then the variation in plasticity characteristics, maximum dry density (MDD), optimum moisture content (OMC), unconfined compressive strength (UCS) and California bearing ratio (CBR) was studied. A decrease in plasticity index (PI) was observed with 3% lime, but with further addition no variation observed. For soil stabilized with fly ash and lime-fly ash admixture no such variation in PI observed. There was a decrease in MDD with the increase in lime and lime-fly ash admixture percentages, but there was a slightly increasing trend with fly ash. No significant variation in optimum moisture content observed with any of the additives. An increase in the UCS of the soil with the curing time and additive percentage was observed. A significant improvement in CBR was observed with lime and lime-fly ash admixtures, but not with fly ash alone. It can be concluded that with 6% lime or 3% lime with 18% fly ash, the required CBR value for the soil to be used as a capping layer material can be achieved