Performance optimization of black cotton soil stabilized with FGD gypsum and cement via response surface methodology.

The growing demand for sustainable infrastructure solutions has driven the exploration of alternative materials for soil stabilization, especially for problematic soils such as black cotton (BC) soil. Owing to its high shrink-swell behavior, BC soil poses significant challenges in construction and pavement applications. This study evaluated the potential use of cement (up to 9.24%), flue gas desulfurization (FGD) gypsum (up to 3.41%), and industrial byproducts from thermal power plants as stabilizing agents to enhance the geotechnical properties of BC soil. A central composite design under the framework of response surface methodology (RSM) was employed to optimize the mix proportions and assess the effects on the unconfined compressive strength (UCS), California bearing ratio (CBR), and plasticity index (PI). The findings demonstrated substantial improvements in soil strength and a significant reduction in plasticity. The optimum mixture of 9.24% cement and 3.41% FGD gypsum yielded a desirability score of 71%, indicating an effective balance between strength gain and workability. This study underscores the viability of using FGD gypsum as a sustainable and eco-friendly soil stabilizer, offering an economical and efficient method for improving subgrade performance in flexible pavement systems. The results contribute to advancing green construction practices by utilizing industrial waste in geotechnical applications.