A Strength–Permeability Study of Steel Slag–Cement–Bentonite Barrier Walls Effect of Slag Substitution Rate and Bentonite Dosage

A barrier wall is a vertical engineered layer designed to block contaminated soil, thereby controlling pollution sources, preventing pollutant migration to groundwater, and limiting pollution spread. Cement–bentonite barrier walls, widely adopted for their seepage control capability, structural strength, and cost-effectiveness, face sustainability challenges due to high cement consumption. This study systematically investigates the coupled effects of steel slag substitution rate and bentonite dosage on the mechanical–permeability of barrier materials for the first time and proposes steel slag (containing dicalcium silicate (C2S) and tricalcium silicate (C3S) phases similar to cement clinker) as a partial cement substitute in steel slag–cement–bentonite barrier materials, aiming to reduce cement usage and utilize industrial waste. Through unconfined compressive strength tests, direct shear tests, and variable head permeability tests, the effects of steel slag substitution rates (0~50%) and bentonite dosages (46~54%) on material performance were systematically investigated. Key findings include (1) unconfined compressive strength decreases linearly with increasing steel slag substitution but grows exponentially with bentonite dosage; (2) cohesion exhibits a negative exponential relationship with steel slag substitution and a linear positive correlation with bentonite content—the unconfined compressive strength of the materials with bentonite dosage of 50% and 54% were 1.51 and 2.84 times higher than those with bentonite dosage of 46%, respectively; (3) cohesion and unconfined compressive strength conform to c = (0.23~0.39)qu; (4) permeability decreases with higher steel slag substitution and bentonite dosage, achieving controlled low permeability (<1 × 10−7 cm/s). This research provides a sustainable solution for barrier wall construction by integrating waste recycling and performance optimization.