Modélisation du séchage des bétons

ABSTRACT A modelling of drying of concrete is presented. « Intrinsic » liquid water (Kl) and gas (Kg) permeabilities are distinguished, since the concept of intrinsic permeability, which is independent of the fluid nature, is not relevant for a cementitious material. New laws for gas transfers are introduced. Thus, a law gives the effective diffusion coefficient of water vapour as a function of porosity and degree of liquid water saturation. In the same way, a new function, expressing the relative permeability to gas according to this degree of saturation, is calibrated thanks to experimental results. In order to describe the global movement of gas, viscous and slip flows are taken into account according to the Klinkenberg's concept. A numerical study shows, on the one hand, that a gas depression (below the atmospheric gas pressure) can be observed and, on the other hand, that transfers of water in the gas phase can significantly contribute to the drying of cementitious materials in addition to liquid water transport by capillarity. Simplified approaches are presented. Finally, a calibration of Kl is carried out thanks to drying experiments.