Effect of the fineness of over-burnt magnesia on the hydration and expansion properties of blended cement

Previous research has indicated that the poor stability of steel slag is caused by the hydration of free calcium oxide and magnesia in the slag, and a great deal of research has been done on the hydration expansion properties of free calcium oxide. However, there is little reported research on the hydration expansion properties of magnesia in steel slag. In this work, the effects of the fineness of over-burnt magnesia on the expansion properties and hydration characteristics of blended cement paste (BCP) were investigated and their correlations were studied. The results indicated that the fineness of the over-burnt magnesia was the intrinsic factor controlling the expansion properties and hydration characteristics of the BCPs. At 20°C, the expansion rate of the BCPs gradually increased with an increase in magnesia fineness increase; however, at 60°C, the expansion rate of the BCPs gradually decreased with increased magnesia fineness. The incorporation of magnesia reduced the cement hydration heat, with a lesser reduction for a greater fineness of magnesia. Furthermore, no great difference in the hydration degree of cement was observed with the use of magnesia of different fineness.