Water sorption isotherms and hysteresis of cement paste at moderately high temperature, up to 80 °C. (March 2023)

• Record Type: Journal Article
• Authors: Wang, Jiayi; Yio, Marcus H.N.; Zhou, Tingtao; Wong, Hong S.; Davie, Colin T.; Masoero, Enrico
• Is Part Of: Cement and concrete research. Volume 165(2023)
• Publication Date: 2023-03
• Subjects: Water sorption isotherm -- Hysteresis -- High temperature -- Modeling -- DFT simulations -- Cavitation -- Dynamic vapor sorption; Cement -- Periodicals; Cement -- Research -- Periodicals; Concrete -- Periodicals; Concrete -- Research -- Periodicals; Ciment -- Périodiques; Béton -- Périodiques; Cement; Concrete; Periodicals; 620.135
• DOI: 10.1016/j.cemconres.2022.107076
• Languages: English
• ISSNs: 0008-8846

Abstract

Abstract: 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. Highlights: Cement paste samples are analyzed using dynamic vapor sorption between 20 and 80 °C. Experiments and simulations indicate that adsorption is near-equilibrium, desorption is not. Higher temperatures shift capillary cavitation towards a higher relative humidity. Higher temperatures also reduce hysteresis at low humidity, associated to interlayer water. A conceptual model is presented to explain the result and refine future engineering models.