Experimental Study on the Solidification of Cold-Region Loess Using EICP with a Waste Steel Slag-Derived Calcium Source Under Freeze–Thaw and Wetting–Drying Cycles in Northwestern China

To address the deterioration of cold-region loess on the northeastern margin of the Qinghai–Tibet Plateau under freeze–thaw and wetting–drying cycles, as well as the reliance of enzyme-induced carbonate precipitation (EICP) on reagent-grade calcium sources, this study developed an EICP system using a calcium source derived from waste steel slag (SS-EICP). A combination of macro- and micro-scale experiments, including unconfined compressive strength (UCS), P-wave velocity, and scanning electron microscopy (SEM) analyses, was conducted to compare the strength characteristics, internal damage, and microstructure of SS-EICP-treated loess with those of CaCl2-EICP-treated loess. The results showed that SS-EICP achieved a UCS of 202.40 kPa at a reaction-solution dosage of 9%, equivalent to 95.9% of the peak UCS of CaCl2-EICP, with an optimum reaction-solution dosage 30.8% lower than that of CaCl2-EICP. After 10 freeze–thaw cycles, the UCS and P-wave velocity loss ratios were 52.22% and 24.54%, respectively; after 10 wetting–drying cycles, the mass loss ratio was 4.59%. Microstructural analysis indicated that cyclic damage mainly resulted from the disruption of CaCO3 cementation and the weakening of interparticle bonding. Overall, SS-EICP combines efficient stabilization at a low dosage with the resource-recovery benefits of waste steel slag, providing a promising pathway toward more sustainable stabilization of cold-region loess.