The constitutive models of concrete often consider water desorption isotherms to be near-equilibrium and significantly affected by moderately high temperature, 40–80°C, typically through microstructural changes. However literature data suggest that adsorption, not desorption, is near-equilibrium and moderate temperatures do not cause microstructural changes. This work supports the latter theory, through dynamic vapor sorption experiments on cement paste at 20–80°C. Samples were pre-conditioned at 60% relative humidity and 20°C, and isotherms were measured for several humidity ranges and testing rates. The results, corroborated by classical DFT simulations, indicate that adsorption is near-equilibrium and mostly unaffected by temperature, whereas desorption is out-of-equilibrium due to the ink-bottle effect at high humidity, and interlayer water at low humidity. Starting from the second cycle, desorption at higher temperatures features a shift of the cavitation pressure and overall a smaller hysteresis. A conceptual model of pore-specific temperature-dependent hysteresis is proposed to qualitatively explain the results.
CITATION STYLE
Wang, J., Yio, M. H. N., Zhou, T., Wong, H. S., Davie, C. T., & Masoero, E. (2023). Water sorption isotherms and hysteresis of cement paste at moderately high temperature, up to 80 °C. Cement and Concrete Research, 165. https://doi.org/10.1016/j.cemconres.2022.107076
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