Innovative processing for cement materials

Hillebrandite can be synthesized by hydrothermal treatment at around 200°C. By heating at 500°C or above, it is possible to obtain β-C₂S without altering the original specific surface area. In other words, ultrafine β-C₂S can be obtained by low-temperature synthesis, without resorting to the process of pulverizing. The β-C₂S from hillebrandite has high hydration reactivity that is dependent on curing temperature. Hydration is completed in 28 d at 25°C and in 1 d at 80°C. The Ca/Si ratio of the C-S-H formed was between 1.95 and 2.0, and almost no Ca(OH)₂ is formed. This type of hydration behavior is quite different from what has been reported in the past. The authors believe that the water film at the time of reaction is very thin, and therefore the reaction progresses in situ, with almost no movement of Ca ions and silicate anions. Such highly reactive β-C₂S has large potential for industrial applications such as belite-based cements. By taking a different approach from the conventional ones for investigating the synthesis of β-C₂S via hydrothermal or mechanochemical treatment, and its attendant behavior, we have been able to show novel characteristics of and new possibilities for β-C₂S.