Study on diffusion and mechanical behaviour of calcium-based solid waste mineralization grouting materials in the goaf

Grouting serves as a critical technique for mitigating goaf subsidence and preventing hazards such as residual coal spontaneous combustion, with its effectiveness fundamentally governed by the diffusion and mechanical properties of the grouting materials. Through integrated experimental analyses, this study systematically investigates the diffusion behavior and reinforcement mechanism of calcium‑based solid waste grouting materials within the void spaces of collapsed gangue in a goaf. The results indicate that the developed carbide slag-fly ash-based mineralized slurry exhibits good flow performance, with an average slump of 27.7 cm and an average flow spread of 48.9 cm. Compared to gravity‑driven upper grouting, pump‑pressure‑driven lower grouting demonstrates superior performance in terms of grouting volume, injection efficiency, and diffusion range. The vertical expansion of gravity-driven upper grouting is better than the horizontal expansion, and the horizontal expansion of pump‑pressure‑driven lower grouting is better than the vertical expansion. Mechanical tests confirm that grouting effectively restrains gangue deformation, substantially reducing the axial strain of grouted specimens compared to ungrouted ones. Field application shows that the maximum surface settlement reduced 20%, while the grouted conglomerate, after 30 days of curing, achieved an average uniaxial compressive strength of 11.72 MPa and an elastic modulus of 0.82 GPa. This study provides a theoretical foundation for the design of efficient goaf grouting.