Permeability, along with diffusion and absorption, is used to quantify dura
bility characteristics of a concrete. The measured value of gas permeabilit
y 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 o
f molecules of the percolating gas, there is some molecular flow which viol
ates the assumptions of the Darcy's law As a result, the coefficient of per
meability varies with the applied pressure. In an attempt to take these eff
ects 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 thi
s purpose, we are characterizing concrete with an intrinsic permeability va
lue. The variation of this intrinsic permeability and that of the contribut
ion of non-viscous flow is studied, for a single concrete mix design in rel
ation to the degree of saturation using a constant head permeametre named a
s CEMBUREAU and oxygen as the percolating gas.