Paste samples of tricalcium aluminate alone, with CaCl 2 , with gypsum, and with gypsum and CaCl 2 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 CaCl 2 to tricalcium aluminate resulted in the formation of 3CaO · Al 2 O 3 · CaCl 2 ·10H 2 O and 4CaO · Al 2 O 3 · 13H 2 O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al 2 O 3 · 6H 2 O; 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 · Al 2 O 3 · CaSO 4 · 12H 2 O and 3CaO · Al 2 O 3 · CaCl 2 · 10H 2 O were the main hydration products.
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Traetteberg et al. (1975) studied this question.
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