Hydration Properties and Technical Behavior of Calcium Sulfoaluminate Cements

Calcium sulfoaluminate (CSA) cements, composed by binary (CSA clinker-anhydrite) and ternary (CSA clinker-Portland cement-anhydrite) mixtures with / molar ratios ranging from 1.9 to 5.0 and Portland cement concentrations comprised between 40% and 70% by mass, were investigated. They were paste-hydrated (w/c mass ratio, 0.5), cured from 4 hours to 28 days and submitted to differential thermal-thermogravimetric (DTA-TG) and X-ray diffraction (XRD) analyses as well as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Expansion of paste specimens cured under water and compressive strength on cement mortars were also determined. Relatively high values of (i) / ratio and solution alkalinity, and (ii) ettringite concentration in the cementitious matrix promoted expansion and compressive strength development, respectively. The formation of expansive ettringite was associated with peculiar SEM and MIP features such as thin [from less than 0.1 µm (0.000004 in) to about 0.3 µm (0.000012 in)] ettringite crystals and pore size distributions shifted toward higher radii, when compared to those related to non-expansive cements.