The substance, Na٢-EDTA, disodium salt of Ethylene Diamine Tetra Acetic
acid, has big influence on the setting time of both Portland cement, and clinker.
The time of initial, and final setting is remarkably changed in the presence of a
small perce
ntage of Na٢-EDTA (less than ١٪ of the cement weight).
The chemical analysis indicates that the total concentration of calcium in the
aqueous phase of cement increases in the presence of Na٢-EDTA. While, the
concentration of free calcium ions in the aqueous phase decreases as the
percentage of Na٢-EDTA increases. Na٢-EDTA forms chelating complexes with
calcium, and some other metals such as iron and magnesium at high PH values,
as in the case of a mixture of cement and water.
