<p>In the comprehensive laboratory study, the limestone slurry waste collected from stone industries during the cutting and processing of limestone is reused to stabilize the clay soil subgrade for road and highway construction. Rather than being disposed of in a landfill, which causes a harmful environmental impact, this waste has a good concentration of calcium ions, which is favorable for enhancing geotechnical properties in subgrade pavement materials. Limestone slurry waste was added at intervals of 5% (by weight of clay) starting from 0 to 25%, and the mixed composition of limestone slurry waste-clay was evaluated based on enhancement in engineering properties of clay soil. Test results show that the incorporation of 20% addition of limestone slurry waste in clayey soil shows the maximum dry unit weight (MDUW) is 17.81 kN/m³ at the optimum moisture content (OMC) of 17.54%. The free swelling index decreases from 51.7 to 21.7% on the maximum addition of 25% limestone slurry waste investigated, showing the reduction in clay soil’s expansive properties. The pozzolanic reaction, increased friction between interparticles, and a denser soil structure were attributed to the maximum California Bearing Ratio (CBR) value achieved at 20% limestone slurry waste addition in both soaked and unsoaked conditions. The results of laboratory investigations, including compaction, Atterberg’s limits test, Swelling index test, and CBR, also indicated that 20% limestone slurry waste addition in clay soil gives the best results to stabilize the clay soil subgrade, which makes the pavement construction sustainable.</p>