Steel Slag and Iron Ore Tailings in Cementitious Mine Backfill: Material Functions, Gel Evolution, and Engineering Selection

Steel slag (SS) and iron ore tailings (IOTs) can reduce cement demand in mine backfill, but strength gains may come with greater flow resistance and processing burdens. This review examines how material functions, gel evolution and interfaces connect treatment to engineering performance, and synthesizes criteria for selecting SS–IOT formulations. SS supplies calcium-bearing hydraulic phases and alkalinity, whereas IOT contributes packing, hydrate-bearing surfaces and mineralogy-dependent chemical participation. Silicate gels develop with ettringite and carbonate-bearing hydrates, influencing interfacial bonding and stiffness. Comparison across studies shows that activator response depends on the complete binder formulation and that strength can increase despite bulk pore coarsening. A gentler post-peak decline can accompany lower peak load capacity. Increasing yield stress and decreasing plastic viscosity exert competing effects on pipeline pressure loss. In the reviewed pre-carbonation series, most estimated carbon savings came from composite-binder substitution, with a smaller increment from treating the slag. These findings support treatment selection based on required strength, deformation capacity, transportability and stability, with process burdens and costs assessed for formulations that meet those requirements. Laboratory, pipeline-loop and field evidence inform the successive measurements needed for scale-up.