Utilization of coal gangue and fly ash for sustainable mine backfill: Rheology and stability optimization of slurry

By systematically optimizing particle size distribution and solid mass concentration, this study develops high-performance coal gangue-fly ash backfill slurry with enhanced rheological properties and stability. X-ray diffraction and performance analyses confirmed that the synergistic combination of crystalline aluminosilicates in coal gangue and amorphous aluminosilicate glass in fly ash significantly contributes to the formation of a cohesive C-(A)-S-H gel network under alkaline conditions, thereby improving the mechanical integrity and stability of the backfill matrix. Slurries with solid mass concentrations between 68% and 76% displayed typical Bingham plastic behavior, with increasing concentration significantly improving both plastic viscosity and yield stress, thus enhancing resistance to bleeding and segregation. Particle size analysis indicated that a distribution modulus of ik = 0.91 effectively minimized bleeding while maintaining high flowability, improving slurry homogeneity and pumpability. An optimal formulation was identified at a 72% solid mass concentration with optimized particle size distribution, providing a balance between workability and stability. These results confirm the potential of coal gangue-fly ash systems as sustainable and cost-effective backfill materials and offer practical guidance for mix design in large-scale underground mining applications. Furthermore, this approach promotes the green reuse of bulk industrial by-products, advancing the sustainable development of solid waste while supporting safe and environmentally responsible mine reclamation.