A Cementitious Compound with Composition 3CaO.Al₂O₃.CaCO₃.11H₂O

The tetracalcium dialuminum hydroxide carbonate pentahydrate Ca₄Al₂(OH)₁₂CO₃.5H₂O is a layered compound constituted by positively charged [Ca₄Al₂(OH)₁₂]²⁺ main layers and negatively charged [CO₃, 5H₂O]^2- interlayers. The Al³⁺ and Ca²⁺ ions are six- and sevenfold coordinated by O atoms, respectively. Water molecules occupy the seventh coordination site of three Ca ions among the four contained in the main layer. Thus, among the five water molecules contained in the interlayer, two of them can be considered as slightly bonded. One O atom of the carbonate group occupies the seventh coordination site of the remaining Ca ion. Moreover, every O atom of the carbonate groups contributes to the formation of relatively strong hydrogen bonds with water molecules, providing cohesion of the interlayer. The planar CO₃^2- groups are tilted by 21.8 (9)° from the planes formed by the layers.

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