In order to study the diffusion and sealing mechanism of an innovative grouted material tentatively called “expandable particulate grout material”, the diffusion process was simulated by the numerical method of CFD-DEM coupling. A numerical model was established for a grouting process in an individual fracture based on the basic physical parameters of expandable particles. The numerical model of the expandable particulate slurry flow was established. The interaction between particles and water in different conditions, such as different grouting times, different volume fractions of the particle, and different velocities, was investigated. The differences in the diffusion process and in the running-water sealing mechanism of expandable particles, cement slurry, and cement-sodium silicate slurry in the crack (in a, in b, and in c) were analyzed. The influence of expandable particles on the streamline of the grout and the drag force in the interaction process under the fracture were analyzed. This is summarized The influence of the velocity ratio of grout to water on different physical quantities, such as diffusion opening degree, diffusion velocity, and diffusion distance, was summarized. It is of significant theoretical and practical value to further develop and improve the grouting technology.

The disposal of industrial solid waste poses significant challenges in the context of sustainable global development. This issue is particularly critical for low-calcium solid waste, which is generated in large quantities and accumulates in extensive stockpiles. Owing to its low reactivity, the high-value utilisation of such waste remains challenging. In this study, three representative and readily available industrial solid wastes—coal gangue (CG), fly ash, and blast furnace slag—were selected for investigation. CG was activated using a combination of chemical, thermal, and mechanical treatments. Experiments were conducted to improve the working performance of CG-based alkali-activated cementitious materials. The microstructural characteristics of the materials were characterised using isothermal calorimetry, nuclear magnetic resonance spectroscopy, and X-ray diffraction. The results indicated that the biomass ash-composite-modified sodium silicate solution provided the best working performance among the activators evaluated, outperforming conventional NaOH and sodium silicate solutions. The thermal activation parameters had a greater influence on the cementitious system than the grinding time. Under the investigated conditions, CG exhibited the highest cementitious reactivity after 2 h of grinding followed by calcination at 800 °C for 4 h. These findings provide a reference for the efficient activation of large quantities of low-reactivity solid waste and support its large-scale, high-value utilisation.