Study on the phase evolution of calcium oxide–silicon dioxide–water system incorporating sucrose under hydrothermal conditions

Abstract

The effect of sucrose on the reaction mechanism and product properties of the calcium oxide–silicon dioxide–water (CaO–SiO2–H2O) system under hydrothermal conditions was investigated. The reaction products with varying calcium oxide to silicon dioxide molar ratio (Ca/Si), concentration of sucrose, reaction temperature and time were characterised by X-ray diffraction, thermogravimetric/differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and acid-insoluble residue analysis. The concentration of Ca2+, pH value and viscosity of the reaction solutions were determined and the influence mechanism of sucrose was then clarified. The results reveal that the phase composition and morphology of the products changed due to the incorporation of sucrose. There was a critical concentration of sucrose (e.g. the sucrose/calcium oxide molar ratio was 0·05 at Ca/Si = 0·8) for the formation of tobermorite. Sucrose promoted the formation of tobermorite when its concentration was lower than the critical value, and retarded the formation once its concentration exceeded the critical value. The morphology of tobermorite changed from plate-like to lath-like or lance-like as the concentration of sucrose increased. In the presence of sucrose, the transformation of tobermorite into xonotlite was inhibited at Ca/Si = 1·0 and the tobermorite phase remained stable even at higher reaction temperatures or for longer reaction times.