Gas permeability of concrete under compressive creep during drying–wetting cycles

Abstract

Gas permeability is used as an indicator of concrete durability due to its strong correlation with material porosity. However, permeability is typically measured on unloaded specimens or under loading conditions that are not representative of actual structural applications. This experimental investigation aims to enhance the understanding of the impact of mechanical stress on the gas permeability and, by extension, concrete durability, under conditions approaching those of structural applications. For this purpose, a novel experimental setup was designed to measure radial gas flow through hollow concrete specimens under compressive creep loading. The setup was validated by comparing the measured gas permeabilities to those obtained using a Cembureau constant-head permeameter. The impact of two levels of compressive creep on the gas permeability of initially saturated concrete specimens was investigated over a 150-day drying period at 20 °C and 50 % relative humidity. Subsequently, the specimens were immersed in water until constant mass was reached and then dried a second time under identical hygro-mechanical conditions, in order to distinguish the effect of water saturation from that of hygro-mechanical cracking. The results show that sustained loading to 30 % of the concrete compressive strength has no significant impact on gas flow. However, loading concrete to 60 % of its compressive strength leads to a tenfold increase in measured gas permeability, compared to unloaded specimens. Monitoring the mass of the specimens revealed that the studied stress levels do not significantly impact drying kinetics. Therefore, the observed increase in gas permeability is attributed to hygro-mechanical damage.