Response Surface Methodology-Based Optimization of Rice Husk Ash and Ground Granulated Blast Furnace Slag Dosage for Alluvial Silty Soil Stabilization

The low strength and large void ratio of alluvial soil (silty) represent a poor quality of subgrade that shows early distress, causing the premature failure of pavement. To enhance the performance of the soil in this context, a mixture of additives such as ground granulated blast furnace slag (GGBS) and rice husk ash (RHA) was applied. Researchers are now very interested in the optimal dosage of stabilizers for increased strength and cost-effectiveness in construction. The dosages analyzed were 5%–12.5% GGBS and 0%–7.5% RHA by weight of dry soil. The following response values were considered: optimum moisture content (OMC), elastic modulus (EM), California bearing ratio (CBR), and unconfined compressive strength (UCS). EM was derived using a novel method of light weight deflectometer testing on the CBR mold. To find the optimal dosage of RHA and GGBS to be added simultaneously for soil stabilization and to examine how these substances affect the soil, response surface methodology models were generated, giving the optimal RHA and GGBS dosages as 2.05% and 7.18%, respectively, to meet desired soil performance. According to the findings, adding GGBS and RHA increased the soil’s strength because of the production of cementitious compounds by pozzolanic reactions, as demonstrated by the mineralogical and morphological examinations of soil specimens. The stabilization resulting from optimal dosages improved the soil UCS by 177%, EM by 47%, and CBR by 242%, and reduced OMC by 4%. This study can provide a strong foundation for effective soil use in road building.