Abstract
• The composition and microstructure of RO phase in two steel slag powder were studied. • The cementitious properties of two steel slag powder and its cement mortars were compared. • RO phase is mainly distributed on the surface of C 2 S. • RO phase with a higher ratio of FeO/MnO wraps C 2 S, seriously inhibiting the hydration process 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 C 2 S. RO phase in G-SSP has a higher ratio of Fe/Mn and wraps a large area of C 2 S, 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 C S H, 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 C 2 S, 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 C S H is formed at later-age, which is connected to each other closely, representing similar later-age cementitious properties to that of P-CMs.
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