Bureau of Standards Journal of Research · 1928 · 14 citations · 0 references
The four calcium aluminates (CaO.Al2O3, 3CaO.5Al2O3, 5CaO.3Al203,3CaO.-Al2O3) have been made, and the mechanism of their reaction with water has been studied. The tricalcium aluminate, 3CaO.Al2O3, reacted so rapidly with water that changes in the composition of the resulting solutions could not be followed. The other calcium aluminates, as well as a high alumina cement, reacted with water to form metastable and supersaturated monocalcium aluminate solutions in the early periods. The metastable solutions decomposed as the reaction proceeded with the precipitation of varying amounts of hydrated alumina and crystalline hydrated tricalcium aluminate, with attendant increases in both the pH and molar ratio, CaO/Al2O3, in the resultant solutions. The constitution of the aluminate solutions has been discussed. Calculations based upon electrometric measurements and chemical analyses indicate that the aluminate in solution is the calcium salt of monobasic aluminic acid. A study of the subsequent changes in the aluminate solutions, attended by increasing concentrations of calcium hydroxide, indicates that a hydrated tetracalcium aluminate may be formed in solutions where the pH value is greater than 12.0. An electrometric titration study of aluminum chloride and calcium hydroxide and an investigation of the calcium chlor-aluminates are described.