Synergistic utilization of co-located high-carbon ferrochrome slag and GGBFS for coastal saline soil stabilization: Performance and Chloride immobilization mechanism

Coastal saline soils present persistent salt-induced geotechnical instability that conventional cementitious stabilizers struggle to mitigate sustainably. This study proposes a novel "near-site threat to treat" strategy by valorizing geographically co-located high-carbon ferrochrome slag (HCFS) and ground granulated blast furnace slag (GGBFS) into an eco-friendly lime-gypsum-activated HCFS-GGBFS binder (LGA-HG stabilizer) for coastal soil solidification and chloride immobilization. Systematic assessments demonstrate that the LGA-HG stabilizer significantly outperforms slag cement, achieving a 28-day unconfined compressive strength (UCS) of 2.5 MPa while effectively transforming moderately saline soils into non-saline forms. Furthermore, the stabilizer exhibits superior long-term durability, characterized by remarkably lower strength and mass losses under severe freeze-thaw and wetting-drying cycles. Microstructural analyses suggest that HCFS, which possesses a potential for aluminum phase release, may continuously release alumina in the later stages. This process is expected to facilitate the transformation of Friedel's salt into the denser and chemically more stable Kuzel's salt, thereby potentially densifying the matrix microstructure. Crucially, environmental and economic assessments indicate that this binder reduces the unit strength cost by 60.7% and carbon emissions by 67.3% compared to traditional cement. Furthermore, under the experimental conditions of this study, no significant leaching toxicity of Cr(VI) was detected. These findings suggest that this stabilizer not only achieves the regional valorization of HCFS, but also provides a techno-economically viable and high-performance solution for sustainable infrastructure development in coastal regions.