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The Role of Sodium Hydroxide in the System C3A-CaSO4-H2O at 30°C

Published online by Cambridge University Press:  25 February 2011

Hanaa Youssef Ghorab  and
Safaa Hussein Abou El Fetouh
Hanaa Youssef Ghorab
Affiliation:
Cement Chemistry Laboratory, University College for Girls, Ain Shams University, Heliopolis, Cairo, Egypt
Safaa Hussein Abou El Fetouh
Affiliation:
Cement Chemistry Laboratory, University College for Girls, Ain Shams University, Heliopolis, Cairo, Egypt
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Abstract

The hydration reaction of C3A with gypsum (molar ratio = 1:1.5) has been studied in water and in sodium hydroxide solutions at 30°C. The hydration product were analyzed microscopically and by means of X-ray diffraction. The concentration of sulfate and aluminum in solution was determined spectrophotometrically. In the absence of alkali, the amount of ettringite formed passes through a maximum and is accompanied by almost complete consumption of sulphate ion in solution. Alkali depresses the formation of ettringite and accelerates that of calcium hydroxide. The monosulfate hydrate appears immediately in alkaline solutions and water then reappears after a day as a solid solution with the tetracalcium aluminate hydrate. The formation of the monophase solid solution is accompanied by the consumption of C3A, ettringite, and calcium hydroxide and by an increase in the amount of the dissolved aluminum. The presence of alkali markedly increases the initial sulfate ion concentration from solution.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 85: Symposium M – Microstructural Development During Hydration of Cement , 1986 , 255
Copyright
Copyright © Materials Research Society 1987

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References

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