Engineering strength through microstructure: gradation and content effects in cemented high-sulfur tailings-crushed rock backfill

This study addresses the environmental hazards posed by the extensive buildup of crushed rock and sulfur-rich tailings produced during mining operations. A complete lab study was carried out to assess strength performance and internal microstructure of a cemented fill system made from high-sulfur tailings and crushed rock (CHSTCRB). UCS trials and SEM inspections were performed based on an orthogonal experimental design. Key parameters, including UCS, critical damage value ( D pk ), failure modes, energy dissipation behavior, and microstructural features, were examined. The findings show that UCS declines as the cement-to-tailing (c/t) ratio drops, with factor influence ranked as follows: c/t ratio having the greatest impact, followed by crushed rock gradation, and then content. Proper aggregate design notably boosts strength while easing degradation effects. The deterioration behavior is ruled by a dual effect of cement hydration and pyrite oxidation, exhibiting a distinct three-stage evolutionary process. Prolonged curing increases D pk , progressively weakening the internal microstructure, enhancing porosity, and resulting in a marked reduction in mechanical strength. As rock content increases and particle size distribution becomes optimized, the failure mechanism transitions from a brittle, tensile-dominated fracture to a hybrid tensile–shear mode, characterized by pronounced stratification and extensive, inter-connected crack propagation. Energy evolution analysis shows a continuous rise in total energy, while elastic strain energy follows a rise–fall trend, peaking before falling as structural damage develops. In the interim, dissipated energy escalates sharply in later steps, revealing intensified damage and fracture activity. An elevated c/t share facilitated cemented materials and basic compaction formations. Extended cure periods enhanced ITZ (interfacial transition zone) contact, and rock aggregate well mitigated worsening of high-sulfur tailings. Accordingly, these findings run a solid scientific basis for optimizing design and engineering application of CHSTCRB systems in contemporary mining operations.