Modelling of isothermal coupled moisture–ion transport in cementitious materials

A numerical model has been developed to predict isothermal coupled moisture–ion transport in cementitious materials. Ionic transport is described by the extended Nernst–Planck equation, which accounts for advection of the liquid phase. Moisture transport includes Fickian water-vapour relative diffusion and Darcian liquid-phase movement. The ion effect on liquid/vapour water equilibrium is taken into account. The variations of the transport properties vs the degree of saturation are described by integral functions or analytical formulas. A Freundlich's type description along with instantaneous Friedel's salt formation is considered for chloride binding at equilibrium. A kinetic equation is added in the cases of non-instantaneous binding processes. The governing equations, as well as the methods of assessment of the material properties required as input data, are described in the paper. Moreover, examples of application of the model in lab conditions are provided, which highlight its capability of predicting moisture/ionic concentration profiles even in complex configurations.