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

Abstract

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 CO32− groups are tilted by 21.8 (9)° from the planes formed by the layers.