Mechanical behavior of waste rock-based geopolymer as a sustainable backfill material: Strength evolution and fracture mechanisms

Green backfill materials enhance slope stability and support sustainable mining in open-pit mines. However, current research mainly focuses on traditional loose fills, neglecting eco-friendly cementitious alternatives. In this study, the potential of waste rock-based geopolymers as mine backfilling materials were proved. Specifically, the compressive strength test was conducted to evaluate the effect of materials interaction, aggregate gradation index, alkali activator dosage, water-to-binder ratio and waste rock utilization rate on the strength. And acoustic emission (AE) technology was used to clarify fracture mechanisms of materials. Results demonstrated high-temperature treatment improves the compressive and flexural strength of waste rock-based paste, with calcined waste rock powder effectively enhancing fly ash reactivity. Increasing slag replacement reduces compressive strength linearly, with 5 MPa decline per 10 % increase in slag content. In addition, specimens with on-site gradation aggregate or higher alkali activator dosage exhibit superior strength. The water-binder ratio around 0.4 and 1:5 waste rock utilization ratio enhances reaction dynamic, maximizing compressive strength. Furthermore, the stress-strain process includes four distinct stages: the compaction and elastic stage, stable crack growth stage, unstable crack growth stage and the post-peak stage. Failure patterns predominantly feature single-slope shear fractures, with cracks concentrated in middle and upper areas of specimen. This study contributes to sustainable resource utilization and green mine construction.