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The hydration of Portland cement, C3S and C2S in the presence of a calcium complexing admixture (EDTA)

✍ Scribed by N.L. Thomas; D.D. Double

Publisher: Elsevier Science
Year: 1983
Tongue: English
Weight: 625 KB
Volume: 13
Category: Article
ISSN: 0008-8846
DOI: 10.1016/0008-8846(83)90039-x

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✦ Synopsis

The effect of EDTA, a calcium chelating agent, on the early hydration of Portland cement, C3Sand B-C2S has been studied by solution analysis and electron microscopy. EDTA is a retarder of cement hydration. Under normal conditions of hydration, the silica levels in solution are very low (<0.05 raM) but in the presence of EDTA an initial flush of silica appears in the bulk aqueous phase. On continued hydration, following the saturation of EDTA with calcium, the appearance of 'free' calcium causes precipitation of C-S-H gel from the bulk solution and changes in microstructure of the colloidal gel around clinker particles in C38 and B-C2S pastes are observed. The action of EDTA as a retarding admixture is explained in terms of the membrane model of cement hydration.

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