OPTIMIZATION OF THE STRENGTH PROPERTIES OF EXPANSIVE SOIL STABILIZED WITH AGRICULTURAL WASTES
Keywords:Expansive soils, Agricultural wastes, Unconfined compressive strength, Expansion index, Response surface methodology
Expansive soils are problematic soils that exhibit shrink-swell behavior. Previous research has shown that 20% rice husk ash (RHA) effectively reduces the swelling potential of expansive soils, but it does not increase the strength of the soil. An improved admixture composed of RHA and a binder was used to treat the expansive soil. Different types of binders were used; three of which are agricultural wastes namely coconut shell ash (CSA), rice straw ash (RSA), and sugarcane bagasse ash (SCBA). Ordinary Portland cement (OPC) was used as a comparison for the other binders. The untreated and treated soil mixtures were evaluated through the unconfined compressive strength (UCS) and expansion index (EI). The effectivity of the admixture is evaluated through ASTM D4609. The treated specimens exhibited an increased in the strength as the curing days increases. A response surface methodology was performed for the UCS of the soil mixtures with the binder types of CSA, RSA, and SCBA. The binder content and curing period are the numerical factors and the response is the UCS. Contour plots and response surface plots showed that the optimum strength for the mixtures with CSA, RSA, and SCBA is at the highest curing period of 35 days and lowest binder content (5% content). The binder type that has the highest maximum value for the predicted response is the RSA, therefore, the optimum mixture is the soil with 5% RSA combined with 20% RHA.