Effects of Magnesium and Chloride Ions on the Early-Age Hydration of C3A in the Presence of Gypsum

Abstract

The chloride binding by tricalcium aluminate (C3A) is a chemical interaction between the hydration products and chloride ions, which has been proven to effectively reduce the deterioration risk of reinforced concrete triggered by seawater. This work aims to explore how aggressive ions, i.e., magnesium ions and chloride ions, affect the early hydration and chloride binding process of C3A in the presence of gypsum. Through a combination of multiscale analyses, this work investigates the roles of magnesium and chloride ions in affecting the hydration kinetics and product phase assemblage of C3A. The results show that magnesium ions could hinder C3A’s hydration through the formation of a dense brucite layer on the hydrated C3A surface, while chloride ions could adversely accelerate C3A’s hydration. Chloride ions are able to react with hydrated C3A to form Friedel’s salt before the depletion of gypsum, and magnesium ions benefit the binding process more than sodium ions.