Hydration of a calcium sulfoaluminate cement blended with zincite
A calcium sulfoaluminate (CSA) cement has been characterised by X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. Selective extraction methods have been used to improve detection limits for identification and quantitative measurements. Perovskites are present in the cement in the form of brownmillerite and a phase with the following average chemical composition Ca1·95Mg0·05Al0·29Ti0·39Fe1·03Si0·22O5·18. The zincite is known as a strong retarder for ordinary Portland cement (OPC), and its effect on the hydration of CSA cement was investigated using isothermal calorimetry, thermal analysis and X-ray diffraction. The low pH of the pore solution in the CSA cement compared to the OPC considerably reduces the solubility of zincite and, at an early age of hydration, zincite behaves as a filler in the CSA cement.