Effect of chloride salts on sulfoaluminate cement hydration

The effect of including 5 % chloride salts (NaCl and CaCl2) on calcium sulfoaluminate cement hydration was studied. The rate of heat release, setting times and mechanical strength were determined in 2 d, 28 d and 90 d cement pastes. The hydration products formed at those ages were identified with XRD and SEM. Hydration reactions were hastened and early age strength heightened with 5 % NaCl. In contrast, 5 % CaCl2 retarded setting times, although it also increased later age compressive strength. The predominant reaction products found in both cases were ettringite and AH3. Chloraluminates such as Friedel’s salt were not observed to form at any of the ages studied. Gypsum precipitation, absent in the reference sample (CSA cement+water), was detected in the presence of chloride salts, however.