2006 Volume 13 Issue 320 Pages 32-39
Effects of two hydrothermal processes, the room temperature and high temperature mixing method, on formation of calcium silicate hydrates were investigated at 250°C from three precursors with Ca/Si ratio of 2.0, β-Ca2SiO4, a mixture of CaO and fine quartz, and a mixture of CaO and amorphous silica. Nine kinds of calcium silicate hydrates were formed, depending on the hydrothermal processes and precursors. γ-C2S hydrate was formed as an initial phase from all starting materials by the high temperature mixing method and from β-C2S by the room temperature mixing method. Low-crystalline C-S-H gel was the initial product from lime and silica by the room temperature mixing method. After the reactions for 1 d, γ-C2S hydrate decomposed to form C8S5 (Ca/Si=1.6) and reinhardbraunsite (Ca/ Si=2.5) by room temperature mixing method. On the other hand, it was first confirmed that jaffeite (Ca/Si=3.0) and kilchoanite (Ca/Si=1.5) were formed through C8S5 from γ-C2S hydrate by high temperature mixing method. The reaction of a mixture of lime and silica by the room temperature mixing method gave hillebrandite (Ca/Si=2.0), but disproportionation reactions proceeded by the high temperature mixing method to form Ca-rich and Si-rich phases.
