Investigation of the Mechanical and Microstructural Properties of Black cotton soil Stabilized with Industrial wastes

• BCS, a highly swelling soil rich in montmorillonite, is unsuitable for many engineering applications. Industrial pozzolanic wastes were used to stabilize it. • Optimum FA–lime mixes achieved 59–66 kg/cm² UCS, while GGBS–lime mixes reached 58–87 kg/cm². • All stabilized mixes fall within the 45–70 kg/cm² UCS range required for pavement base courses as per IRC:37-2018. Black Cotton Soils (BC soils) are highly prone to swelling and shrinkage due to their high montmorillonite content, often causing damage to pavements, dams, reservoirs, and multi-storey buildings. This study aims to reduce the stresses these soils exert on flexible pavement structures. Considering the environmental impact of cement, the research investigates the use of Ground Granulated Blast Furnace Slag (GGBS), lime, and fly ash (FA)—both individually and in combination—to improve soil properties sustainably. Various mix ratios were tested to identify the most effective combinations. Mechanical characterization included Atterberg limits, maximum dry density (MDD), optimum moisture content (OMC), and unconfined compressive strength (UCS). Microstructural characterization was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to examine mineralogical changes and the formation of cementitious phases. Chemical characterization assessed pozzolanic and cementitious reactions induced by lime, FA, and GGBS, resulting in the formation of calcium silicate hydrates (C–S–H) and calcium aluminate hydrates (C–A–H). Results showed that lime–GGBS mixtures provided the highest UCS (6.72–9.56 MPa) and durability, while lime–FA combinations also improved UCS (3.05–6.74 MPa). Cement additions (3–10 %) achieved UCS of 0.8–6 MPa after 7 days. Durability was maintained up to 30 % FA and 20 % lime, with higher proportions reducing performance. Overall, the study concludes that combining lime, FA, and GGBS effectively stabilizes Black Cotton Soils, enhancing strength and durability to meet IRC:37–2012 standards for pavement base layers, while minimizing environmental impacts compared to conventional cement stabilization.