Evolution of gas permeability for concrete materials under and after uni-axial loading

Under life-cycle service conditions, gas permeability which is usually employed to indicate the durability performance of concrete materials will be changed along with the evolution of microstructure under or after loading. This paper reports an extensive experimental research on the influence of loading condition on the evolution of gas permeability. A cyclic loading scheme under displacement control, which is employed to accelerate the evolution of its microstructure and model the loading condition under real service, is applied on cylinder specimens ϕ37u74mm dried to constant weight at 60°C. Both axial and lateral strains in the whole loading test are recorded by strain gauge to characterize the change of microstructure macroscopically. At the same time, gas permeability measurement is carried out by a well-designed tri-axial permeater at various loading levels in the planned loading history. The relationship between intrinsic gas permeability, Klinkenberg coefficient and residual strains discussed. It is found that intrinsic gas permeability will become great if the uniaxial loading level is beyond about 70% ultimate strength. Moreover, both the klinkenberg coefficient and intrinsic gas permeability are badly linked with elastic and plastic strains. However, the relationship between the Klinkenberg coefficient and intrinsic gas permeability can be approximated by a semi-empirical law, no matter under or after loading