Mechanical properties and microscopic features of LBM-GGBS solidified saline soil in seasonally frozen areas

Light-Burned Magnesia (LBM) activated Ground Granulated Blast Furnace Slag (GGBS) is established as a promising and robust binder for soil stabilization. However, its durability in saline environments subjected to freeze-thaw (F-T) cycles lacks systematic investigation. To validate its potential for subgrade engineering in seasonally frozen regions, this study evaluates the mechanical and microscopic properties of LBM-GGBS solidified saline soil under F-T cycling. The effects of LBM and GGBS on the unconfined compressive strength (UCS), permeability coefficient, Cl^- leaching and microstructures of solidified saline soil after different F-T cycles (0, 2, 4, 6, 8, and 10) were examined. The results showed that increasing the LBM-GGBS content significantly enhanced the soil's resistance to F-T cycles. With a 12% LBM-GGBS content and a GGBS/LBM ratio of 7 (determined as the optimal mix proportion), the solidified soil reached a residual strength of 3 MPa after 10 F-T cycles, which was four times the strength required for the upper base layer of highway pavement subgrade. Microscopic analysis revealed that the LBM-GGBS solidified soil exhibited a dense structure with calcium silicate hydrate (C-S-H), magnesium silicate hydrate (M-S-H), hydrotalcite, and Kuzel salt as the primary reaction products. The formation of these hydration products significantly densified the structure, thereby increasing the strength and improving the F-T resistance of the solidified soil. Furthermore, ~ 75% of Cl^- in the original saline soil could be stabilized even after multiple F-T cycles. These findings elucidate the micro-mechanism of chloride stabilization under freezing conditions and provide a robust theoretical foundation for utilizing LBM-GGBS to mitigate saline soil hazards in seasonally frozen regions.