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

Blends consisting of sulfoaluminate-belite (SAB) cements and Portland cement (PC) (CEM 1 42-5) were tested. The initial set of PC was 3h 10min, of SAB-1 cement lOmin and of SAB-2 cement 20min, whereas those of blends 85wt% SAB-1 and 85wt% SAB-2 were lh lOmin and 30mm, respectively. It is suggested that differences in the mineralogical composition of SAB cements influence markedly the setting characteristics of blended cements with very similar fineness. Properties of cement mortars (cement: sand = 1:3 by weight, water/ cement ratio = 0.5) containing PC/SAB cement in weight ratios of 100/0, 85/15, 70 /ʹ30, 55/45, 15/85 and 0/100 were tested in more detail. Flexural and compressive strength of mortars made from PC/SAB-1 cement blends are lower than in PC-mortar kept for 90 days at 20°C/100% relative humidity (wet cure) and 20°C/60% relative humidity (dry cure). SAB-I cement and the 85 wt% SAB-I/15 wt% PC blend have shrinkagecompensating properties opposite to PC in tested mortars. PC-mortar shows excellent protective properties against corrosion of steel reinforcement. Steel in the SAB 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 85wt% SAB-I/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 SAB-I cement by PC is still sufficient for steel passivation.