In-situ reaction of the very early hydration of C3A-gypsum-sucrose system by Micro-Raman spectroscopy

This paper studied in situ, by Micro-Raman spectroscopy, the very early hydration of C3A in the presence and absence of sulphates and with sucrose as an additive. For C3A hydration in the absence of gypsum, when carbonation is not avoided, carbonate-AFm phases are formed, but in the presence of gypsum, hydroxi-AFm are the main phases. Ettringite is the AFm stable phase developed initially at 70 min of hydration with gypsum and no monosulphate is formed. In the presence of sucrose, this salt, instead of sulphate, is adsorbed over the surface of the C3A, avoiding its reaction with sulphates until sucrose desorption. Three hours are necessary to lead to ettringite formation. A nucleation poisoning/adsorption surface mechanism is proposed for added sucrose systems.