Hydration of β-dicalcium silicate at high temperatures under hydrothermal conditions

Hydration of β-dicalcium silicate was carried out under hydrothermal conditions at different temperatures from 50 °C to 400 °C up to 5 days by using two methods to start the reactions at room temperature or at a desired reaction temperature. 9 C-S-H phases with the same Ca/Si ratio as precursor (γ-dicalcium silicate hydrate and α-dicalcium silicate hydrate and dellaite), Ca-rich compositions (jaffeite and reinhardbraunsite), Si-rich compositions (Ca₈Si₅O₁₈, kilchoanite and foshagite), and C-S-H gel were obtained at the initial stage of the hydration of β-dicalcium silicate. The reaction products were different in dependence in the hydrothermal processes. It was found that α-dicalcium silicate hydrate was directly formed from β-dicalcium silicate at low temperatures below 220 °C. The products obtained at above 240 °C were different in dependence in the hydrothermal processes, due to the different decomposition route of γ-dicalcium silicate hydrate, the initial product from β-dicalcium silicate. The room temperature mixing method gave reinhardbraunsite and kilchoanite through Ca₈Si₅O₁₈. In the case of the high temperature mixing method, γ-dicalcium silicate hydrate decomposed to from Ca₈Si₅O₁₈ and reinhardbraunsite with jaffeite, then Ca₈Si₅O₁₈ decomposed to from jaffeite and kilchoanite, and final products at 400 °C were reinhardbraunsite and foshagite which was formed from kilchoanite.