Flowability, Carbon Sequestration, and Strength Properties of Carbonation-Cured Solid Waste-Based Backfilling Materials

To address the critical challenges of low industrial solid waste utilization, excessive CO₂emissions, and land subsidence in coal mine goaf areas, this study developed an innovative solid waste-based backfill material (SFC) through CO₂-activated curing of steel slag, fly ash, and coal gangue (CG). The research systematically evaluated the SFC slurry’s flow characteristics, carbon sequestration capacity, and mechanical strength following CO₂curing. The results indicate that the slurry yield stress and thixotropy initially increase and subsequently decrease with the rising CG content. Among the tested formulations, SFC5 exhibits the highest yield stress (171 Pa) and thixotropic hysteresis area (11,198 Pa/s). Nevertheless, all SFC formulations meet the minimum flowability requirements for underground mine backfilling applications. Besides, both carbon sequestration efficiency and compressive strength increase with extended curing age, whereas at 21 days of CO₂-activated curing, these properties decrease with rising CG content. Significantly, all formulations except SFC20 exceed the 6 MPa threshold required for mine backfill applications. And when the utilization of CG is considered, SFC15 is the optimal material combination that achieves the best balance of flowability, carbon sequestration, and strength properties. This study develops an SFC backfill material that complies with mine backfill specifications, establishing a scientific basis for integrated management of coal-metallurgical solid wastes and CO₂sequestration.