A study of the performance of subgrade expansive soils modified with molasses and cement

Abstract

The performance of a road pavement predominantly depends on the quality of the subgrade because it’s the support system of the pavement, hence requires to be considered promptly in the design. In areas with poor and expansive subgrade soils, the pavements always experience structural and functional distresses due to the predominance of the montmorillonite clay mineral, which has an unstable lattice structure in the soil. This calls for methods to provide a suitable subgrade for enhanced pavement quality and durability. With the diversity of these methods, stabilization has proved more feasible because of its cost effectiveness and time efficiency. In this project research, an investigation was carried out to assess the impact of stabilizing subgrade expansive soils (black cotton soils) with mollasses and cement. Research was done on expansive clay soil sample from Lomori mor road, Nakapiripiriti district, with addition of cement alone and combination of cement and molasses in concentrations of 13% cement, 8% Cement + 4% Molasses, 6% Cement + 8% Molasses and 4% Cement + 4% Molasses each by dry weight of the soil. For the analysis of the effect of the stabilizer on soil, comparison was made on geotechnical properties of the native soil and stabilized soil which was done by carrying out Atterberg’s limit test, maximum dry density (MDD) test and California Bearing Ration (CBR) test on both the native soil and stabilized soil. The addition of cement on the sample soil gave significant improvement in strength and eliminated swelling properties of the native soil. Application of molasses on soil-cement mixture improved the soil-cement reaction with water causing larger size grains and increased soil strength. Addition of 4% molasses to 4% cement increased CBR value of 12.03% of the native soil to 21.80% and reduced 51.5% PI value of the native soil to 19.2%. Therefore; soil stabilized with 4% molasses and 4% cement combination satisfied all specification requirements for stabilized sub-grade soil and also gave the least cost estimation of 189,672,000 Ugshs per 1km chainage of the road and hence selected as the optimum stabilizer content for sub-grade soils.