Mechanistic Insights into a Sustainable Mechanochemical Synthesis of Ettringite.

Mechanochemistry offers an environmentally benign and facile synthesis method for a variety of cement paste constituents. In addition, these methods can be used to selectively tune the properties of cement components. The mineral ettringite is an important component of cementitious materials and has additional technological potential due to its ion exchange properties. Synthesis of ettringite via mechanochemistry is an environmentally friendly alternative to conventional wet-chemical synthesis established in industry. This contribution explores the mechanism of a two-step mechanochemical synthesis of ettringite, which was previously found to greatly improve the reaction conversion as compared with one-pot synthesis. The crystallinity of Al(OH) was found to decrease during the first stage of this mechanochemical synthesis. This was correlated to a significant decrease in the particle size of Al(OH) in this stage. No other significant changes were found for the other components, suggesting that mechanochemical activation of Al(OH) is responsible for the enhanced formation of ettringite by the two-step approach. The environmentally friendly approach developed for ettringite synthesis offers a versatile synthetic strategy, which can be applied to synthesise further cementitious materials.