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
