Gas permeability of concrete in relation to its degree of saturation

Permeability, along with diffusion and absorption, is used to quantify durability characteristics of a concrete. The measured value of gas permeability of concrete depends strongly on its degree of saturation. Moreover, when the size of pores is of the same order of magnitude as the mean free path of molecules of the percolating gas, there is some molecular flow which violates the assumptions of the Darcy's law As a result, the coefficient of permeability varies with the applied pressure. In an attempt to take these effects into account, we have tried to quantify different types of flow and we propose a method to calculate the apparent coefficient of permeability and hence the gas flow through concrete having any given degree of saturation and being under a given pressure difference across its extremities. For this purpose, we are characterizing concrete with an intrinsic permeability value. The variation of this intrinsic permeability and that of the contribution of non-viscous flow is studied, for a single concrete mix design in relation to the degree of saturation using a constant head permeametre named as CEMBUREAU and oxygen as the percolating gas.