Case study on coal-based solid waste utilization in backfill paste: Hydration mechanism and performance analysis

This study investigates the hydration mechanism and performance of backfill paste in coal mine filling applications, aiming to address issues related to solid waste accumulation and surface damage in coal seam mining. Through a comprehensive analysis integrating micro observation, macro testing, and on-site monitoring, the study elucidates the three-stage hydration process, highlighting the interplay between fly ash and cement. SEM and XRD reveal early hydration products, primarily flocculent hydrated calcium silicate (C-S-H) and needle-like ettringite (AFt). Reactive substances in fly ash fully react, generating substantial C-S-H, enhancing later paste strength. Field application in an eastern coal mine demonstrates the paste’s evolving microstructure and increasing load-bearing capacity, effectively supporting overlying rock layers at 1 MPa and 3.5 MPa in the early and later stages, respectively. In the actual filling environment, the strength of the filling paste is strengthened. After 170 days, maximum density is attained, and the paste provides complete support with a stable deformation of up to 30.3 mm. Critical safety measures for preventing and managing blockages in the filling pipeline are outlined based on practical experience. The findings provide valuable insights into optimizing backfill paste formulations and operational protocols to enhance efficiency and safety in coal mine filling operations. This method serves as a valuable reference for promoting and utilizing paste filling mining in similar contexts.