Performance Research on Slag-Steel Slag Based Composite Portland Cement

Using slag, steel slag and Portland cement as the raw material with a small amount of activator, the composite Portland cement of magnitude 42.5R was prepared.The steel slag fineness, the composite ratio of slag-steel slag and the types of activator on the properties of composite Portland cement were studied in the research.The hydrated products of composite Portland cement and the micro-structure of harden cement paste were analyzed by SEM.The results show that the greater the specific surface area of steel slag is, the shorter the setting time, and the higher the mortar strength will be.The cement setting time is prolonged, the expansion rate is increased and the mortar strength is decreased with the increase of the percentage of steel slag in composite Portland cement.The activity of slag and steel-slag is increased, the setting time is shortened and the mortar strength of each age is significantly increased with the adding of alkaline activator to composite Portland cement.Besides, SEM photos show that adding sodium silicate makes the cement hydration accelerated, C-S-H gel and -crystal continuously formed, the bonding degree of cement and aggregate increased，the gap of cement paste decreased and filled with hydration products.