Vacuum Modular Concept, a new technique to measure air permeability: application to anisotropy in reinforced concrete

The permeability of concrete is a key parameter to evaluate the durability of reinforced concrete structures. In the nuclear field, the tightness of containment buildings largely depends on the low permeability of prestressed concrete. These structures are heavily reinforced raising the question of how reinforcement bars and prestressing cables affect the apparent permeability compared to plain concrete. Usual standardized permeability tests have limitations. The small sample size makes it challenging to study the effects of reinforcement. Additionally, confinement within test cells can alter interface quality, potentially closing cracks in damaged concrete. This can modify the flow characteristics and impact the representativeness of the measured permeability. To address these issues, a new apparatus has been developed to measure permeability under vacuum for reinforced concrete elements. The measurement is performed on prismatic specimens in two directions. This paper presents the system and its validation on plain concrete, as a preliminary step before applications on reinforced concrete. The results indicate a significant anisotropy in permeability depending on the orientation of reinforcement bars. The experiments reveal the minimal resistance of steel-concrete interfaces to pressure gradients, irrespective of the saturation degree.