Investigation of coal-based solid waste grouting materials for environmental repair

Surface cracks and water-conducting fissures from coal mining have caused severe environmental issues. One solution to repair the environment is to backfill the coal mines with coal-based solid wastes (CBSW). In this study, the slurry properties, macro-mechanical strength, and microstructure characteristics of three CBSW-based grouting materials are studied with uniaxial compressive strength tests, X-ray diffraction analysis, and scanning electron microscopy-energy dispersive spectroscopy tests. The composite materials mix cement with fly ash, desulfurized gypsum, or coal gangue. The cement-fly-ash composite materials exhibit the best compressive strength among the three groups, with the highest strength value of 19.56 MPa after the 28-day curing. The influence of water-solid ratio, cement-CBSW ratio, additive content, and curing time on the mechanical properties is comprehensively investigated. The compressive strength of the grouting materials continuously increased through curing, accompanied by porosity reduction. The properties of the slurry reach a good balance when the water-solid and cement-CBSW ratios are 0.8:1 and 1:0.6, respectively. This study proposes a methodology for environmental grouting repair in mining areas and improves the CBSW utilization.