Crystal transformation of calcium silicate minerals synthesized by calcium silicate slag and silica fume with increase of C/S molar ratio

Abstract

In order to accurately control the crystal of calcium silicate minerals synthesized by hydrothermal using calcium silicate slag and silica fume, the dynamic hydrothermal synthesis experiments of calcium silicate minerals were carried out using calcium silicate slag and silica fume under different C/S molar ratios. And the phase species, micromorphology, micropore parameters of the hydrothermal synthesis were analyzed by XRD, SEM, EDS and micropore analysis. The results show that the main mechanism of hydrothermal synthesis reaction is that β-calcium silicate, the main mineral in calcium silicate slag, rapidly hydrates to form Ca(OH)2 at high temperature and high pressure hydrothermal synthesis conditions, and then Ca(OH)2 reacts with Si and Al groups in amorphous silica fume to form different crystal of calcium silicate minerals which C/S molar ratio is similar to total C/S molar ratio of raw materials. With the increase of C/S molar ratio, the crystal of the main hydrothermal synthesis changes in the order of petal-like C–S–H, silk-like Gyrolite, long flake-like Tobermorite, fiber-like Xonotlite and short flake-like Scawtite. And when the main phase is petal-like C–S–H, the average pore volume, average pore diameter and specific surface area of hydrothermal synthesis are the largest. However, when the main phase is fiber-like Xonotlite, the average pore diameter of hydrothermal synthesis is larger, but the average pore volume and specific surface area are the smallest.

Keywords

• Calcium silicate slag
• Silica fume
• Hydrothermal synthesis
• Calcium silicate minerals
• Crystal transformation