Kinetic modelling of dynamic vapour sorption for predicting equilibrium isotherms in alkali-activated binders

Abstract Moisture content in porous concrete, which depends on environmental relative humidity, is a key parameter in durability tests of construction materials. Relative humidity affects the amount of free water within the pore network, which serves as a medium for corrosive agents to diffuse through the concrete and reach the embedded steel reinforcement. The correlation between environmental relative humidity and the degree of saturation is described by water vapour sorption isotherms, which address the equilibrium between the sorbed and free liquid phases in the pores at a given temperature. However, limited data are available on water vapour sorption isotherms for alkali-activated materials, and such measurements require long durations to achieve equilibrium at each relative humidity condition. In this research, several kinetic models used in sorption analyses are tested on data from Dynamic Vapour Sorption measurements for alkali-activated binders, with varying microstructures, to predict water vapour sorption isotherms in a realistically shorter experimental timeframe. Among the models tested, the Weibull distribution model best predicts the final measurements at equilibrium, and with the model a new testing parameter termed as mass conversion can be used as an indicator to reduce the experimental duration for determining water vapour sorption isotherms.