Study on the interface transition zone of steel slag-based backfill materials stabilized by different alternative binders

Abstract Current research on the microstructural mechanisms governing the stabilization of steel slag aggregates with inorganic binders remains limited. To address this knowledge gap, this investigation comparatively analyzes the interfacial transition zone (ITZ) in steel slag composites stabilized by cement versus solid waste-based alternative binder. Through microhardness testing and micro-region XRD characterization, distinct interfacial characteristics were identified: the steel slag-cement and steel slag alternative binder ITZ exhibited widths of approximately 60 μm and 200 μm, respectively. Phase composition analysis revealed enhanced complexity in ITZ regions. The cementitious ITZ contained supplementary Ca(OH) 2 and tricalcium aluminate phases compared to the cement matrix, while the alternative binder-based ITZ demonstrated higher residual C 2 S content relative to its matrix. The comprehensive evaluation combining unconfined compressive strength (UCS) and leaching tests shows that this alternative binder has certain performance advantages, especially in the later stage of strength development, it has obvious progressive advantages. The alternative binder-treated specimens achieved 56%, 60%, and 84% of cement-stabilized UCS values at 7d, 28d, and 90d respectively, while exhibiting superior frost resistance. Notably, chromium leaching concentrations were reduced to 79.58% of cement-stabilized levels and 23.20% of untreated steel slag.