Mixture-proportioning design of cement soil containing Pisha sandstone for mine filling

The Ordos area, known for its abundant coal reserves, faces significant environmental challenges annually due to coal mining. This mining activity not only leads to extensive mining subsidence and environmental pollution but also exacerbates soil erosion, exacerbated by the region's weakly cemented pisha sandstone. Addressing these issues, filling mining offers a viable solution by substituting underground mineral resources with filling materials, thereby mitigating environmental harm and facilitating sustainable resource utilization. In coal-rich cities such as Ordos, a pressing concern is developing effective methods to prepare mine-filling materials using locally abundant resources. This work delves into the effect of varying mix proportions on the strength of cement-solidified Pisha sandstone and its underlying microscopic mechanisms. Using the simplex centroid design method, we predicted the 28-d compressive strength of cement-solidified Pisha sandstone with a compound binder. Building on previous research, we formulated a strength formula for cement soil with a compound binder. By correlating the measured 28-d compressive strength with the known mix proportions of Pisha cement soil, we estimated the 28-d compressive strength of the mixture Our findings confirm that both the simplex centroid design method and strength formula can accurately predict the 28-d compressive strength of stabilized Pisha sandstone with the compound binder. Our experimental design, encompassing the simplex centroid design method, regression formula, and specific strength formula, was obtained from a limited set of tests. Incorporating the required compressive strength of cement soil into both the strength and regression formulas allows for more accurate proportion determined through mutual verification of these methods. We discovered that blending Pisha sandstone with cement significantly effects the mixed material's strength, and that substituting cement with ground granulated blast-furnace slag (GGBS) can enhance economic efficiency. Microstructural analysis of cement soil revealed that the strength enhancement by cement and GGBS is due to their hydration products filling the pores in Pisha sandstone, creating a unique structure. The results of this study have far-reaching implications, particularly in promoting the use of modified Pisha sandstone as mine-filling material. This approach not only addresses the management of problematic regional soils but also contributes to the ecological restoration of mining areas.