Feasibility study and performance optimization of sand-based cemented paste backfill materials

Cemented paste backfill (CPB) mining is widely applied in coal mines throughout China, where gangue rock is commonly used as an aggregate. However, some mining areas do not have an abundant supply of gangue. This paper proposes a sand-based cemented paste backfill material (SCPB) with widely distributed and low-cost Yellow River sand as the filling aggregate with cement and fly ash as the binders based on the mining conditions of the Zhaoguan Coal Mine located in the Shandong province of China. The conveying and mechanical properties of the material were tested and optimized. This study found that (i) the initial SCPB have a large bleeding rate, while the early and late strengths are generally low; (ii) simultaneously adding polycarboxylate and quicklime can significantly improve the engineering performance of the filling material, where the bleeding rate is 3.2%–3.9%, the early strength is 0.2–0.39 MPa, and the late strength is 7.53–8.86 MPa; and (iii) the optimal mixing ratio of the SCPB concentration is 78%, the F/S ratio is 0.6, the C/S ratio is 0.2, the P/S ratio is 0.004, and the L/S ratio is 0.15. Furthermore, the X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that the optimized SCPB was denser than the initial SCPB and exhibited a greater degree of fly ash hydration. [Display omitted] •Engineering performance metrics of cemented paste backfill materials were given.•Weaknesses of sand-based cemented paste backfill materials and their causes were analyzed.•Best ratio of sand-based cemented paste backfill material was obtained.•Microstructural features of sand-based cemented paste backfill materials were analyzed.