Performance analysis and acoustic emission characteristics of multi-source coal-based solid waste backfill materials at different curing temperatures

With increasing mining depth and the widespread adoption of functional backfill mining, the ambient rock temperature rises progressively. Concurrently, the hydration heat released by backfill materials materials during hardening creates a highly complex internal temperature field, which exerts a significant influence on both the mechanical properties and microstructure of the backfill. In this study, multi-source coal-based solid waste (MCSW) backfill was cured under five different curing temperatures (20–60 °C) for durations ranging from 1 to 28 days. Rheological properties and uniaxial compressive strength were measured, while acoustic emission (AE) was employed to monitor energy release and crack propagation in real time. Microstructural evolution was further characterized by mercury intrusion porosimetry (MIP) and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS).The results show that as slurry temperature increases, yield stress and apparent viscosity first decrease and then increase. Increasing curing temperature and age exhibit dual effects on strength, elastic modulus, and AE peak energy: namely, strengthening at moderate levels but deterioration at excessive levels. Furthermore, the spatial distribution of AE source events first concentrates and then gradually disperses, while the proportion of micro and small pores first increases and then decreases. The optimal mechanical properties are achieved at a curing temperature of 50 °C and a curing age of 14 d. However, high-temperature curing accelerates the evaporation of free water, and an excessively prolonged curing age inevitably causes water shortage, thereby interrupting the continuous hydration reaction and inducing thermal damage. This, in turn, destroys the C‑S‑H gel and internal pore network, adversely affecting long‑term strength development. Therefore, appropriately increasing curing temperature and age accelerates internal hydration, reduces void structures, and thus improves the overall mechanical properties of the backfill materials.