Study on the flow properties of modified magnesium-coal-based solid waste carbon sequestration backfill materials

To address greenhouse gas emissions and massive solid waste in coal industry activities, carbon sequestration backfill materials have been explored, with the fluidity of these materials being a critical factor in the backfill process. In this study, CO₂-modified magnesium-coal based solid waste backfill materials (CO₂−MCSB) were prepared. The flow and rheological properties of CO₂−MCSB under different mass concentrations and cementitious material ratios were examined through slump, rheological, bleeding tests, and microscopic analyses. The impact of secondary aeration on CO₂ uptake and fluidity was explored by modifying the rheological testing apparatus by using selected parameter combinations: FA50–74 from the mass concentration group and FA40 from the cementitious material ratios group. The results showed that increasing mass concentration reduced slump (142.5 to 132.0 mm), expansion (50.8 to 25.0 cm), and bleeding rate (6.03 % to 2.21 %), while increasing yield stress, plastic viscosity, and thixotropy. Conversely, increasing the proportion of fly ash in cementitious material raised slump (134.0 to 138.0 mm), expansion (29.9 to 36.0 cm), and bleeding rate (2.01 % to 2.78 %), while reducing yield stress, plastic viscosity, and thixotropy. The rheological behavior of CO₂−MCSB slurry conforms H-B model, with strong linear correlations between flow and rheological parameters. Furthermore, studies on FA50–74 and FA40 about secondary aeration demonstrated that secondary aeration not only improved the fluidity of CO₂−MCSB slurry but also increased CO₂ uptake by 21.86 % and 21.75 %, respectively. This study provides valuable insights for designing and optimizing the material ratios of carbon sequestration backfill slurries to achieve desirable flow properties in engineering applications.