Effect of Lime on Hydration of Pastes Containing Gypsum and Calcium Aluminates or Calcium Sulfoaluminate |
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| Authors: | P. K. MEHTA |
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| Affiliation: | Department of Civil Engineering, University of California, Berkeley, California 94720 |
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| Abstract: | Chemical reactions responsible for ettringite formation in the commercial expansive cements are reviewed. X-ray diffraction analyses of the hydrated expansive compounds showed that in the presence of Ca(OH)2 and CaSO4 the tricalcium aluminate hydrated very slowly and the monocalcium aluminate quickly, whereas the calcium sulfoaluminate hydrated at a uniform rate during the early hydration period. Scanning micrographs are presented which show that ettringite formed in the presence of Ca(OH)2 is colloidal. It is proposed that colloidal ettringite can adsorb large quantities of water, thereby causing slump loss in fresh concrete and expansion in hardened concrete. |
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