Effects of Doping Glass Fibers on the Early Strength of Sand-Based Cemented Paste Backfill for Solid Wastes Disposal in a Coal Mine

The mechanical strength of cemented paste backfill (CPB), especially the early compressive strength, is crucial for controlling the overlying rock movement. Therefore, improving the early compressive strength of CPB is a critical issue. In this study, the doped glass fibers’ effect on the macroscopic mechanical strength and microstructural features of the sand-based CPB (SCPB) with different curing ages was analyzed. The macroscopic properties and the microstructure of SCPB were characterized experimentally and analyzed via scanning electron microscopy. The results showed that slump sizes of SCPB specimens without and with doped glass fibers were 269 and 209 mm. Thus, doped glass fibers inhibited the SCPB transportability and significantly improved its early compressive strength. At curing ages of 1 d and 3 d, the compressive strength of SCPB specimens doped with glass fibers was improved by 679 and 278%, respectively, compared to the blank control group. As the curing age increased, the compressive strength improvement of the SCPB doped with glass fibers was gradually saturated. Finally, the correlation between macroscopic and microscopic properties of SCPB specimens was analyzed comparatively. Thus, the mechanism of doped glass fibers’ influencing the early compressive strength of the SCPB was revealed. The research findings provide theoretical guidance for improving the SCPB early compressive strength at the mining site with the CPB mining technique.