Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement

摘要

The availability of cements, including eco-cements, with tailored mechanical properties is very importantfor special applications in the building industry. Here we report a full study of the hydration of calciumsulfoaluminate eco-cements with different sulfate sources (gypsum, bassanite and anhydrite) and twowater/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known tostrongly modify the mechanical properties of the resulting mortars and concretes. The applied multitechniquecharacterization includes: phase assemblage by Rietveld method, evolved heat, conductivity,rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfatesources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initialsetting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydritedissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that ingypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars withslightly higher compressive strengths. Ettringite content is the chief parameter to explain the strengthdevelopment in these eco-cements.