Carbonation of γ-Ca₂SiO₄ and the Mechanism of Vaterite Formation

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The carbonation of γ-Ca₂SiO₄ (γ-C₂S) and mechanism of vaterite formation have been investigated by evaluating the crystal structures of both γ-C₂S and vaterite. The samples used were autoclaved calcium silicate hydrate hardening bodies prepared from Ordinary Portland Cement (OPC), γ-C₂S and α-quartz and then subjected to accelerated carbonation. The ratio of OPC to γ-C₂S was varied. Ca²⁺ in both γ-C₂S and vaterite was found to be coordinated to six O^2-. In addition, both γ-C₂S and vaterite have similar atomic arrangements of O^2- and Ca²⁺ and Ca-O bond distances. Therefore, it is proposed that vaterite mainly forms from γ-C₂S via a topotactic reaction during accelerated carbonation.