Influencing mechanisms of RO??????? phase on the cementitious properties of steel slag powder

Steel slag powder (SSP) reveals the potential to act as a supplementary cementitious material (SCM) due to its similar composition to that of cement. However, the influencing mechanisms of RO phase (MgO-FeO-MnO solid solution) on the cementitious properties of SSP is still unclear, which inhibits the comprehensive utilization of SSP. In this paper, the cementitious properties of SSP and its cement mortars (CMs) was investigated, aiming to explore the action mechanisms of RO phase. The chemical composition, mineral phases, microstructure, elemental distribution, particle size distribution and specific surface area of two types of SSP (G-SSP and W-SSP) were identified. In addition, the difference in mechanical properties and hydration products between their CMs were also discussed. Results show that the two kinds of SSP exhibit similar chemical and mineral composition and their RO phase is mainly distributed on the surface of C2S. RO phase in G-SSP has a higher ratio of Fe/Mn and wraps a large area of C2S, thus leading to a higher average particle size and smaller specific surface area of G-SSP. And its CMs demonstrate far inferior early-age and later-age cementitious properties without obvious CSH, indicating a big gap with the cementitious properties of plain cement mortars (P-CMs). While RO phase with a lower ratio of Fe/Mn in W-SSP is only dispersed at the edge of C2S, causing a lower average particle size and larger specific area of W-SSP. Its CMs also display poor early-age cementitious properties with quite loose hydration products. However, a large amount of CSH is formed at later-age, which is connected to each other closely, representing similar later-age cementitious properties to that of P-CMs.