The main hydration reaction product in the ternary system fly ash, calcium sulphate and calcium aluminate cement (40/20/40) at 20°C is a hydrated calcium sulfoaluminate compound, an AFt phase slightly different from “traditional ettringite”. The carbonation of ettringite develops gypsum but in this case rapidcreekite is formed. For the first time it has been observed that carbonation of the mentioned calcium sulfoaluminate compound (AFt), an hydrated calcium sulphate carbonated phase (Ca2(SO4)(CO3)·4H2O) is formed with the replacement of an SO4 row in a (0 4 0) layer of the gypsum by CO3 groups. The developed carbonated phase has been studied and analyzed through XRD, FTIR, Raman spectroscopy, and scanning electron microscopy.

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