Absorption and Hydration Behavior of Tricalcium Aluminate-Water and Tricalcium Aluminate-Gypsum-Water Systems in the Presence of Superplasticizers

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Title: Absorption and Hydration Behavior of Tricalcium Aluminate-Water and Tricalcium Aluminate-Gypsum-Water Systems in the Presence of Superplasticizers

Author(s): V. S. Ramachandran

Publication: Journal Proceedings

Volume: 80

Issue: 3

Appears on pages(s): 235-241

Keywords: adsorption; calcium aluminate hydrates; calorimeters; conductivity; C3A; ettringite;gypsum; hydration; melamine resins; napthalene compounds; plasticizers; sulfonation.

Date: 5/1/1983

Abstract:
Additions of I, 2, and 4 percent sulfonated melamine or naphthalene formaldehyde retard the hydration of C,A and the rate of conversion of hexagonaf to cubic aluminate hydrate. This effect is more pronounced at high dosages of the superplasticizer. Rate of adsorption of the superplasticizer is higher in the CA-H,0 system than in the hexagonal or cubic phase; adsorption is irreversible. In a non-aqueous medtum only the hexagonal phase adsorbs small amounts of superplasticizer. Reaction between tricalcium aluminate and gypsum to form ettringite is accelerated in the presence of superplasticizer. The exothermal reaction occurring in this system as a result of the reaction of excess tricalcium aluminate b delayed in the presence of the superplasticizer. Adsorption experiments on the tricalcium aluminate-gypsum mixture prehydrated for different periods show that the rate of adsorption is generally in the decreasing order 0, I hr. 2 days, I5 min, 30 min, and 5 min. In the non-aqueous medium only small amounts of superplasticizer are adsorbed. Adsorption was irreversible in all cases.