Divergent durability mechanisms of sulfoaluminate cement and cement-sodium silicate grouts in aggressive coal mine groundwater

The long-term safety of coal mine underground reservoirs (CMURs) relies critically on the durability of dam reinforcement materials. While cement-sodium silicate (CS) grout is widely employed for emergency plugging, its reliability under prolonged exposure to aggressive mine water is compromised compared to emerging alternatives like sulfoaluminate cement (SAC). This study investigates the strength evolution and deterioration mechanisms of SAC grout, utilizing CS grout as a comparative benchmark. Through 140-day immersion tests, wet-dry (WD) cycling, quantitative microstructural analysis, and numerical modeling, the divergent evolutionary paths of these materials were elucidated. Experimental results demonstrate that SAC exhibits a high stability characteristic, maintaining constant compressive strength as porosity decreases to 3.05 %. Conversely, CS grout suffers significant strength retrogression driven by intrinsic interface-induced syneresis and microcracking. Numerical simulations based on Fick’s second law quantify a critical regime shift in mass transport: while erosion in the dense SAC matrix is restricted to slow Fickian diffusion, the micro-cracked CS matrix succumbs to a rapid, coupled convection-diffusion mechanism. Consequently, chemical accumulation in CS structures reached approximately three times that of SAC after one year. Furthermore, a deterioration model based on Grey System Theory GM(1,1) was established to forecast SAC strength deterioration under extreme WD cycling. From an engineering perspective, the results provide a practical basis for selecting grout types in CMURs: SAC is better suited for long-term/permanent dam reinforcement and seepage control, whereas CS is more appropriate for emergency plugging where rapid setting is prioritized. These findings confirm that SAC possesses superior microstructural integrity that prevents the transition from diffusive to advective erosion, validating its suitability for permanent reinforcement in aggressive subsurface environments.