Investigations on Water Vapor Adsorption–Desorption of Cementitious Materials and Its Induced Permeability under Isothermal Steady-State Flow

H2O(g) adsorption-desorption of cementitious materials and their permeability is a vital indicator for their durability designs, which significantly affects the occurrences of corrosion, carbonization and freeze–thawing, but its quantitative characterization has yet to be investigated in depth. In this study, H2O(g) adsorption-desorption of cementitious materials with various w/c ratios (0.35–0.55) and its induced permeability were investigated using a self-created cup apparatus under isothermal steady-state flow and compared with N2 gas permeability by the modified Cembureau method. The results showed that the cementitious materials with a low w/c ratio have stronger water-holding characteristics, and there is an obvious inflection point in the adsorption curve [i.e., relative humidity (RH)=70%]·H2O(g) permeability measurement of cementitious materials was successfully carried out using a self-created cup apparatus, which is fundamentally an exponential function relationship to its N2 gas permeability. The conversion relation is helpful to enhance the multimedium evaluations of durability for cementitious materials.