Experimental Investigations of Diffusive and Convective Transport of Inert Gas through Cement Pastes

In the context of the temporary near-surface storage of intermediate-level radioactive wastes, different concepts of waste packages are considered Most of them are composed of an external container made of fiber reinforced concrete, receiving several primary waste packages. Self-radiation of encapsulating matrices can lead to the continuous production of hydrogen, which, for obvious safety reasons, must be drained out of the container Concrete, seen as an heterogeneous porous medium, can offer a path for gas transfer through its porosity. Then, the transport mechanism depends mainly on the production rate: the diffusion process takes place for a low production rate of hydrogen whereas permeation corresponds to a high production rate. This paper focuses on transport properties of the cement paste, which is the main porous component in concrete. The experimental investigation of gas diffusion and permeation through the cement paste porosity shows that the gas transfer ability of the material depends on two interdependent factors: the water saturation state and the microstructural properties of the material. In the context of cement-based materials, these two dimensioning parameters are mainly controlled by the formulation of the cement paste as well as the curing and operating conditions. The influence of these parameters on the diffusion and permeation properties of the cement pastes is experimentally evaluated.