Prediction of the relative permeability to gas flow of cement-based materials

Abstract

The macroscopic physical modeling of coupled air and water transport in unsaturated porous material requires transport coefficients for the two phases along with the diffusion coefficient of vapor in air. As their experimental determination is often difficult and time consuming, relations have been proposed for a long time to allow the calculation of all the needed parameters, starting from experimental properties that are easier to obtain, such as water pressure head as a function of the degree of saturation or isothermal sorption curves. These relations, validated for soils, are also used for cement, mortars or concrete, although they have not been really justified in these cases. The aim of this study is to determine if soil physics principles can be applied to unsaturated moisture movement in concrete. We measured the air permeability of concrete specimens from which we obtained the relative permeability. Evidently, the parameters introduced in the relations given by Van Genuchten [Ann. Geophys. 3 (1985) 615] have to be revised. New values are proposed for the parameters for the concrete studied. These values are justified by the good reproduction of the experimental air permeability and airflow evolution observed during experiments.