ABSTRACT
Abstract Permeability of concrete may depend on the aggregate content because : • the permeability of the two components, cement paste and aggregate, are different, • the tortuosity of the porous paths, the volume fraction of ITZ and their connectivity
increase with the aggregate content. Gas permeability of cement based materials depends on the microstructure and also
on the degree of saturation. The influence of ITZ on gas permeability has been studied on mortars specimens with different sand volume fractions. By conditioning the specimens prior to the gas permeability measurements, the water distribution into the material is modified. Following the Kelvin Laplace equation and assuming an equilibrium, the conditioning treatment implies a maximum pore size dm to be full of water. If the tested cement based material contains an interconnected pore system which dimension is greater than dm, the gas permeability should be affected. In that sense, gas permeability is a test which allows us to detect the evidence of an interconnected pore system greater than dm. If the pore size is greater than dm in ITZ, gas permeability data should indicate the connectivity of ITZ pores. An experimental program has been conducted with two W/C ratios (W/C = 0.5 and 0.35). With the lowest W/C ratio, two types of specimens have been tested : a first series with an OPC as binder and a second series with OPC and silica fume.
