Rheological, Carbon Sequestration, and Mechanical Properties of Solid Waste-Based Carbon-Negative Backfill Materials: Effect of Reaction Temperature

Utilizing coal-based solid waste (CSW) for carbon-negative backfill mining offers a promising pathway for CSW disposal and CO 2 sequestration. However, the influence of reaction temperature on the rheological, carbon sequestration, and mechanical properties of the CSW backfill material remains unclear. In this study, coal gangue, fly ash, slag, and cement were used, and a temperature-adjustable carbonation testing system was employed to prepare and carbonate the CSW backfill material. Experimental groups were tested at reaction temperatures from 25 to 130 °C. Through thermogravimetric analysis, rheological tests, unconfined compressive strength (UCS) tests, and microscopic characterization, the effects of reaction temperature on carbonation rate, rheological, and mechanical properties were studied. The results show that the rheological behavior conforms to the Herschel–Bulkley model, and the yield stress increases with reaction temperature due to accelerated hydration and moisture evaporation. Once the reaction temperature reaches 85 °C, the yield stress exceeds the industrial pumping limit. The maximum carbonation rate of 5.23% and UCS 7.08 MPa were attained at 55 °C. This is due to increased reactivity of alkaline minerals and accelerated hydration at higher reaction temperatures. These findings provide theoretical support and key technical parameters for the optimization and engineering application of the CO 2 sequestration process of CSW backfill material.