Investigation on the effects of combining lime and sodium silicate for expansive subgrade stabilization

Abstract

Expansive clay is unsuitable subgrade material covering about 40% of the area of Ethiopia. Engineering  properties of such problematic soils can be improved by chemical stabilization. This study investigated the effects of combining slightly alkaline liquid sodium silicate with hydrated lime for stabilization of expansive clay. The experimental study involved Particle-Size Analysis, Atterberg Limits, Standard Compaction and California Bearing Ratio tests. Expansive clay was combined with 2, 4and 6% of lime; 1, 2.5and 6% of liquid sodium silicate and the respective combinations of the two additives by dry weight of the soil. Test samples were typically soaked for 30minutesto account for strength loss due to compaction delay. Samples were cured for 3 and 7 days before testing for Atterberg Limits and  California Bearing Ratio values. Additional 28 days of curing were considered for Atterberg Limits test samples. Test results manifested that sodium silicate  reduced plasticity indexes by least12% compared to untreated soil. Expansive soil treated with sodium silicate or combination of lime and sodium silicate resulted in unusual compaction curves from which maximum dry densities and optimum moisture contents could not be determined. Sodium silicate and its combination  with lime decreased shear strength and increased  swelling properties of expansive clay compared to the respective lime series. Curing enhanced strength  development and reduced swelling properties of treated soils. The study revealed that sodium silicate or its combination with lime is not a suitable means of expansive clay stabilization.

Keywords: California Bearing Ratio, Dry Density, Expansive Clay, Lime, Plasticity Index, Sodium Silicate, Soil Stabilization