Hydration heat evolution, non-evaporative water, setting time and SEM tests were peorormed to investigate the effect of fine steel slag powder on the hydration process of Portland cement and its mechanism. The results show that the effect of fine steel slag powder on the hydration process of Portland cement is closely related to its chemical composition, mineral phases, fineness, etc. Fine steel slag powder retards the hydration of portland cement at early age. The major reason for this phenomenon is the relative high content of MgO , MnO2, P2O5 in steel slag, and MgO solid solved in C3 S contained in steel slag.
