Influence of Reconstruction Process Parameters on the Mineral Phase Evolution and Hydration Properties of High-Iron-Phase Steel Slag

This study developed a high-iron-phase steel slag-based silicate cement system through high-temperature reconstruction and multi-source solid waste synergistic modification. The effects of reconstruction temperature and Ca/Si ratio on burnability, mineral evolution, microstructure, and hydration performance were investigated. Results showed that carbide slag and bauxite significantly improved the sintering behavior of steel slag. At 1275 °C, the f-CaO content in reconstructed steel slag decreased sharply from 1.45% to 0.11%, while overburning and liquid-phase coating occurred at 1300 °C, hindering further reaction of residual f-CaO. Reconstruction promoted the conversion of low-reactivity γ-C2S to active α-C2S and the formation of well-crystallized C4AF. The decomposition of the RO phase enabled Mg2+ and Mn2+ to solid-solve into spinel phases, thus improving volume stability. The Ca/Si ratio regulated intermediate phases: higher ratios favored C4AF, whereas lower ratios promoted spinel or olivine phases. The optimal sample (1275 °C, 65% steel slag + 25% carbide slag + 10% bauxite) achieved a 28 d compressive strength of 107.56 MPa, 18.26% higher than the reference cement, owing to synergistic hydration of α-C2S and C4AF. The F4 sample showed the lowest residual CH content (11.31%) and the highest hydration efficiency.