An experimental study on the upgrade of sulfoaluminate-belite cement systems by blending with Portland cement

Blends consisting of sulfoaluminate-belite ((S) over bar AB) cements and Portland cement (PC) (CEM I 42.5) were tested The initial set of PC was 3 h 10 min, of (S) over bar AB-1 cement Ia min and of (S) over bar AB-2 cement 20 min, whereas those of blends 85 wt% (S) over bar AB-1 and 85 wt% (S) over bar AB-2 were Ih 10 min and 30 min, respectively. If is suggested that differences in the mineralogical composition of (S) over bar AB cements influence markedly the setting characteristics qi. blended cements with very similar fineness. Properties of cement mortars (cement:sand = 1:3 by weight, water/cement ratio = 0.5) containing PC/(S) over bar AB cement in weight ratios of 100/0, 85/15, 70/30, 55/45, 15/85 and 0/100 were tested in more detail Flexural and compressive strength of mortars made from PC/(S) over bar AB-1 cement blends are lower than in PC-mortar kept for 90 days at 20 degrees C/100% relative humidity (wet cure) and 20 degrees C/60% relative humidity, (dry cure). (S) over bar AB-1 cement and the 85 wt% (S) over bar AB-1/15 wt% PC blend have shrinkage-compensating properties opposite to PC in tested mortars. PC-mortar shows excellent protective properties against corrosion of steel reinforcement. Steel in the (S) over bar AB cement mortar is not passivated but occurs in the nonstable state. The related pH values of the mortar extracts were 12.41 and 11.32, respectively. In the 85 wt% (S) over bar AB-1/15 wt% PC-mortar the steel is protected against corrosion. This statement is confirmed by the pH value of the mortar extract of 11.88. A 15 wt% replacement of (S) over bar AB-1 cement by PC is still sufficient for steel passivation.