Time dependency and similarity of gas permeability of concrete in simulated environment

Abstract

It is of great significance to establish the similarity for time-dependent permeability between simulated environment and natural environment for predicting the time-dependent permeability in practical engineering. Based on the exposure test of ordinary concrete in natural tidal environment and simulated environment, the time-dependent intrinsic gas permeability coefficients (Kg) of concrete were analyzed, and the influence of w/c ratio on Kg and age reduction factor of gas permeability coefficient (mg) was studied. According to the relaxation time tracked by the nuclear magnetic resonance (NMR) method, the time-dependent microstructure parameters of concrete in the natural and simulated environments, such as porosity, pore size distribution, capillary pores porosity, critical pore diameter (Dcd) and mean pore diameter (Dmd) were analyzed. Then, the relationship between the time-dependent gas permeability and microstructure parameters was discussed. Results show that Kg decreased with the increasing exposure time and decreasing w/c ratio. The value of mg decreases with the increasing w/c ratio, and for concrete with the same w/c ratio, mg in the simulated environment is larger than that in the natural tidal environment. Porosity, capillary pores porosity and Dcd of concrete all decrease with exposure time, and have good correlations with gas permeability coefficient (KA) of concrete. Meanwhile, ambient environment has little influence on the correlation between gas permeability and Dcd. At last, based on the similarity between Kg and microstructure parameters in the natural and simulated environments, the rationality of calculating the long-term Kg in natural environment from the short-term results in the simulated environment is verified.