Influence of temperature on water vapour sorption isotherms and kinetics of hardened cement paste and concrete

Water vapour sorption isotherms (WVSIs) have contributed significantly towards current knowledge of the porous nanostructure of cementitious materials and are an important component in modern durability calculations. In this paper, two newly developed multi-chamber testing apparatus for determining WVSIs of hardened cementitious materials are described. The adsorption, desorption and scanning behaviour of hardened cement paste and concrete are studied in detail over temperatures of 23°C to 80°C. Experiments provide confirmation of a monotonic reduction in sorption hysteresis with increasing temperature and show a disappearance of low humidity hysteresis by 60°C. Time and history dependence of apparent isosteric enthalpy of adsorption is demonstrated. Typically overlooked anomalous (non-Fickian) sorption kinetics are observed to significantly influence the equilibrium process. The magnitude and effect of temperature and humidity on kinetics is examined. Evidence supporting the role of microstructural change in observed size-independent kinetics and WVSI changes with temperature are discussed.