Assessment of cement dust with anhydrite as an activator for granulated slag

Supersulphated cement is based on granulated slag activated by anhydrite and portland cement clinker or lime. In the present work, the washed and calcined cement dust is used instead of cement clinker with anhydrite for activation of slag. A highly alkaline medium from calcined cement dust may be used to provide this alkalinity. The sulphate activation of slag by anhydrite leads to the formation of ettringite al the early ages of hydration. At later ages of hydration, CSH (tobermorite-like phase) is formed. The rate of reaction was studied with chemical; DTA and XRD techniques. The results revealed that the calcination of washed cement dust at 1100, 1200 and 1300 degrees C for 2 hrs decreases the amounts of Na2O, K2O and Cl- whereas the SO3 increases up to 1200 degrees C then decreases. On the other side, the phases of beta-C2S, C(4)AF, C3S and C(6)A(4)MS were also formed then increased with firing temperature. The activation of slag increases with the calcination temperature of cement dust as well as the anhydrite content. Also, the present investigation indicates the possibility for utilization of washed and calcined cement dust in the production of supersulphated cement.