STABILIZATION OF EXPANSIVE SOIL USING WHEAT STRAW ASH AND CALCIUM CARBIDE RESIDUE COMPOSITE

Abstract

Expansive soil is a problematic soil. It has properties of expansion, shrinkage, plasticity and low bearing capacity, which makes them inadequate for use in construction. Two industrial wastes, Calcium carbide residue (CCR) obtained from acetylene gas plants and Wheat straw ash (WSA) obtained from Oil mill boiler, are used as composite binder for stabilization of expansive soil. The influential factors studied were binder ratio and curing time. At first, expansive soil was stabilized with WSA, to find the optimum WSA content based on UCS results. It was found out to be 12.5% and was fixed as total binder content in this study. The (CCR:WSA) binder was added to soil in ratios of 0:100, 10:90, 25:75, 50:50 and 75:25, by replacing WSA with CCR in binder. Experimental investigations were done to study the compaction, plasticity, strength and deformation behavior of soil stabilized with composite binder (CCR:WSA). Microstructural analysis was also performed to study the mineralogical and morphological modifications happened during stabilization process. XRD, SEM and EDX tests were done for this purpose. It was observed that plasticity index, swelling pressure and swelling percent decreased after addition of CCR:WSA binder in expansive soil. Shear strength and unconfined compressive strength (UCS) increased after stabilization with composite binder. UCS of CCR:WSA stabilized soil increased by 35 times the original soil. SEM, EDX and XRD validate the findings of UCS and direct shear test. These tests have shown that the strength increase is caused by development of cementitious hydrates which are produced as result of reaction between Calcium hydroxide from CCR and (SiO2 + Al2O3) from WSA and soil. CCR:WSA ratio of 75:25 was recommended for obtaining the best results for stabilization of expansive soil. This study has proved that (CCR:WSA) composite binder is an effective, economical and environment friendly solution for stabilization of expansive soil