Hydration properties of the composite cementitious materials containing steel slag under steam curing condition

Steel slag (SS) is a by-product of steel industry, and its recycling is of great significance. In this study, the influence of SS fineness and curing regimes on the hydration properties of cement and the effects of SS content on the compressive strength of pastes were investigated. The hydration products and microstructure of pastes were further explored through X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The results show that the compressive strength decreases gradually with the increase of SS, and increases with the increase of the specific surface area of SS. The compressive strength of paste after steam curing is improved, and the compressive strength of the paste mixed with 30% SS can reach more than 50 MPa after 90 days of steam curing. The hydration products of paste mixed with SS is not significantly different from that of cement, which is mainly composed of Ca(OH)₂ and C-S-H gel, accompanied by a small amount of CaCO₃. SS has secondary hydration in long-term age and can fill and refine the pore structure, according to SEM. Using SS as supplementary material is beneficial to reducing cement cost and lowering CO₂ emission.