Physically and chemically bound H2O in the α-C2S hydrate structure

Abstract

In this work, a study of water vapour sorption by α-C2S hydrate in a different humidity was done, and the stability of mentioned calcium silicate hydrate structure dependence on the partial pressure of water vapour was examined. Also, the theoretical calculations of hypothetical reactions parameters between water and α-C2S hydrate are presented. It was determined that at 25 °C temperature, the water vapour pressure (p/p 0) over α-C2S hydrate influences the quantity of adsorbed water in the samples. According to simultaneous thermal analysis results, in a 30–230 °C temperature range, when p/p 0 varies from 0.355 to 0.87, the values of process heat (Δq r = −17.4 J g−1) and mass loss (Δm r = 2.8 %) slowly increased and showed the possibility of physical adsorption. Meanwhile, at higher water vapour pressures (>0.87), the values of mentioned parameters (Δq r = −426 J g−1; Δm r = 25.5 %) significantly increased, suggesting that the condensation of water vapour occurred in the pores. Also, it was examined that at higher temperatures (390–510 °C), the decomposition reactions of α-C2S hydrate and intermediate compounds proceeded, during which Δm r decreased to 2.45 %, while Δq r to −39.13 J g−1. In addition, the probable mechanism of α-C2S hydrate thermal decomposition is confirmed by thermodynamic calculations and also by the instrumental analysis data.