Impact of Utilizing Industrial Waste for Stabilizing Chemically Contaminated Clay Soils: A Sustainable Method to Improve Soil Durability

The stabilization of sulfate-contaminated clayey soils remains a significant challenge in geotechnical engineering due to the formation of expansive minerals such as ettringite and gypsum that cause strength loss and structural deterioration. This study evaluated the mechanical behavior and durability of sulfate-contaminated kaolinite clay stabilized with industrial by-products including lime, fly ash, and ground granulated blast-furnace slag (GGBS). Soil samples collected from south of Tehran were treated with 6% lime, 12% slag, and a combined 4% lime + 12% slag, cured for 28 days at 35 °C, and subjected to unconfined compressive strength (UCS), wet–dry (W/D), and freeze–thaw (F/T) tests under Na₂SO₄ and MgSO₄ contamination. Results showed that 20% fly ash increased UCS from 987.2 kPa to 1480.8 kPa (≈50% improvement), while 12% slag reduced free swelling from 8.2% to 3.3% (≈60% reduction). The lime–slag mixture achieved the highest UCS (1985.1 kPa) and maintained durability indices of 0.52 under W/D and 0.23 under F/T cycles, outperforming single stabilizers. Sodium and magnesium sulfates caused 69–77% UCS reduction after six F/T cycles, yet the blended system significantly mitigated deterioration. The enhanced performance is attributed to synergistic pozzolanic–hydraulic reactions forming C–S–H and C–A–H gels, which densify the soil and inhibit sulfate-induced expansion. Overall, the 4% lime + 12% slag blend provides a sustainable and chemically stable alternative for improving sulfate-affected clayey soils while reducing carbon emissions associated with conventional stabilizers.