Pre-reaction temperature effect on C–S–H colloidal properties and xonotlite formation via steam assisted crystallization

Abstract

The pre-reaction temperature effects on the crystallization and micro-structure of xonotlite for C–S–H gels with Ca/Si ratio = 1 using a steam assisted crystallization process was investigated. The pre-reaction temperature affected the crystallinity, pore structure and silicate chain structure of C–S–H gels, thereby influencing the xonotlite micro-structure and formation kinetics. A higher Q2/Q1 Si peak intensity ratio were observed in C–S–H gels pre-reacted at 80 °C, indicating that a higher pre-reaction temperature can promote condensation reactions between the Si–OH units, and hence transforming of silicate chain structure from a single chain structure to a double chain structure. The XRD background intensities around 2Θ = 20°–35° resulting from the occurrence of amorphous C–S–H phase decreased as the pre-reaction temperature increased, suggesting that the pre-reaction temperature can increase the degree of structural order and crystallinity. More xonotlite were formed for C–S–H gels pre-reacted at 40 °C and 60 °C after reacting at 180 °C for 32 h and 190 °C for 16 h compared to the sample pre-reacted at 80 °C, due to the decrease of the solubility resulting from the increase of the average silicate chain length and the decrease of Ca/Si ratio after pre-reaction at 80 °C.