Hydration of 3CaO·Al2O3 and 3CaO·Al2O3+] Gypsum With and Without CaCl2

• Published in: Journal of the American Ceramic Society 1975-05, Vol.58 (5-6), p.221-227
• Main Authors: TRAETTEBERG, AUD, GRATTAN-BELLEW, P. E.
• Format: Article
• Language: English
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1975.tb11450.x

Paste samples of tricalcium aluminate alone, with CaCl2, with gypsum, and with gypsum and CaCl2 were hydrated for up to 6 months and the hydration products characterized by SEM, XRD, and DTA. Tricalcium aluminate hydrated initially to a hexagonal hydroaluminate phase which then changed to the cubic form; the transformation rate depended on the size and shape of the sample and on temperature. The addition of CaCl2 to tricalcium aluminate resulted in the formation of 3CaO · Al2O3· CaCl2·10H2O and 4CaO · Al2O3· 13H2O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al2O3· 6H2O; the addition of gypsum resulted in the formation of monosulfoaluminate with a minor amount of ettringite. When chloride was added to tricalcium aluminate and gypsum, more ettringite was formed, although 3CaO · Al2O3· CaSO4· 12H2O and 3CaO · Al2O3· CaCl2· 10H2O were the main hydration products.