Effect of temperature on the initial properties of calcium sulfoaluminate binders synthesised at 1100°C

Abstract

In this investigation, it was studied the effect of curing temperature on the mechanical properties of pastes made with calcium sulfoaluminate cements synthesised from industrial wastes at a relatively low temperature of 1100°C. Fluorgypsum, fly ash, aluminium slag and calcium carbonate were used as raw materials. The main phases of synthesis were calcium sulfoaluminate and gehlenite. Pastes were prepared with different water/cement ratios, 15-25 wt-% hemihydrate and cured at 20 and 40°C. It was found that with higher total amounts of sulphates and increase in temperature, compressive strength is enhanced in the first days of curing and setting times decreased. Ettringite was found to be the main reaction product forming dense structures over time. Calcium sulphates hydration changed the ettringite formation causing fluctuations in the strength development, nevertheless, in some cases the strength surpassed 40 MPa at 28 days. Microstructures and hydration products were studied by SEM and XRD.