Study on Feasibility and Performance Optimization of Cemented Paste Backfill Materials Prepared from Coal-Based Solid Waste

Aiming at the high costs and material shortages in coal mine cemented backfill mining, this study develops a promising coal-based solid waste backfill material considering massive output and the low utilization of solid waste from large coal–electric–chemical bases. Targeting the strike-along longwall subsequent grouting backfill, proportion optimization tests on coal-based solid waste cemented paste backfill (CSWCPB) are conducted. The effects of the material composition on the slurry workability and the mechanical properties and microstructure of the hardened backfill are analyzed, and a corresponding backfill system design is proposed. The results indicate that the uniaxial compressive strength rises first and then falls with increasing coal gangue content. Fly ash reduces the early strength yet enhances the later strength via the pozzolanic reaction. The optimal ratio of backfill materials is coal gangue content of 0.22 kg, fly ash content of 0.75 kg, gasification slag content of 0.14 kg, and a slurry mass fraction of 76%. A full system containing ground slurry preparation, gradient-based pipeline transportation, and backfill mining parallel working-face subsystems is established. This study supports green coal mining and large-scale coal-based solid waste disposal in ecologically fragile zones.