Application of dilatometric analysis to the study of autoclaved calcium silicate materials
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The process of shrinkage of calcium silicate hydrate was investigated by dilatometry up to 350 °C. The properties of this material are based on the formation of C–S–H phases during the reaction at temperatures between 180 and 205 °C and water vapor pressure lower than 16 bars. The main C–S–H phases are 11.3 Å tobermorite and xonotlite. 11.3 Å tobermorite converts to 9.3 Å tobermorite on air at temperatures around 300 °C. The hydrosilicate materials were prepared from quicklime and finely ground sand with different CaO/SiO2 ratios under different hydrothermal conditions. The reaction time was 24 h. Materials based on xonotlite and tobermorite were produced, and the calcium silicate phases were characterized by XRD and TG/DTA methods. Dilatometry measurements were used to study the effect of heating conditions on sample shrinkage. Dehydration of hydrated calcium silicate minerals occurred during heating. The results show that sample shrinkage is dependent on the type and amount of C–S–H phases, the amount of bound water and formation of 9.3 Å tobermorite. All samples showed shrinkage after heating up to 350 °C, but this change was not irreversible for all samples after cooling to room temperature.
KeywordsCalcium silicate hydrates Dilatometry Shrinkage Tobermorite Xonotlite
This paper was elaborated with the institutional support for long-term development of research organizations by the Ministry of Industry and Trade of the Czech Republic.
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