Mechanical performance and damage mechanisms of steel slag-cement pasted backfill under high-temperature cured and cyclic static loading for deep-mining applications

Applying steel slag (SS) to mine backfilling not only alleviates environmental pressure caused by solid waste disposal but also provides a cost-effective and high-performance filling material for mining operations. Although SS-based backfill (SS-CPB) has been widely used in shallow surface mining, its mechanical properties under deep mining conditions still require further investigation. This study examines the mechanical properties and damage evolution patterns of SS-CPB under the combined effects of high-temperature curing and cyclic loading. The results indicate that as the curing temperature increases, the peak strength, elastic modulus, and stress yield level of SS-CPB exhibit an initial increase followed by a decrease. At a curing temperature of 60 °C, SS-CPB achieves its maximum peak strength (5.11 MPa), elastic modulus (0.61 GPa), and stress ratio (σc/σp) of 94.6%. High-temperature curing enhances the hydration reaction of SS-CPB and accelerates the crystallization of C–S–H gel, leading to increased material brittleness, The brittleness indices of SS-CPB under curing conditions of 20 °C, 40 °C, 60 °C, and 80 °C are 40.2%, 56.6%, 76.5%, and 95.5%, respectively. Consequently, the failure mode transitions from tensile failure to a combined “tensile + shear” failure mode. With increasing mining depth and geothermal temperature, the plasticity and ductility of the backfill material are enhanced after cyclic static loading. The coupled effect of fatigue loading and high-temperature conditions intensifies the propagation of initial pores and microcracks in the interfacial transition zone (ITZ), resulting in a more developed “tensile + shear” crack network in the specimens.