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