Gas and water permeability of concrete

Abstract

AbstractConcrete is used as a barrier on surface or near-surface facilities for the final disposal of low- and intermediate-level radioactive waste, where gas can be generated and affect the hydraulic properties and the processes taking place in concrete. In this framework, gas-transport properties of concrete samples were investigated using two different laboratory test set-ups: a non-steady-state equipment working under low injection pressures; and a newly fine-tuned steady-state set-up working under different pressures.Permeability decreased with water content increase but was also greatly affected by the hydraulic history of concrete (i.e. if it had been previously dried or wetted). The intrinsic permeability determined with gas flow was about two orders of magnitude higher than that determined with liquid water (10−16 v. 10−18 m2), probably due to the chemical reactions taking place during saturation (carbonation). The relative gas permeability of concrete increased sharply for water degrees of saturation smaller than 50%.The boundary conditions also affected the gas permeability, which seemed to be mostly conditioned by the back pressure and the confining pressure, on the whole decreasing as the effective pressure increased. It is considered that the Klinkenberg effect was not relevant in the range of pressures applied.