Time Dependency and Similarity of Water Permeability of Fly Ash Concrete Between Laboratory Environment and Site Environment

Effects of fly ash (FA) content and environmental factors on the water permeability were studied, and the similarity relationship of time-dependent water permeability coefficient in site and laboratory environment was discussed. Meanwhile, the main microstructure parameters and their time-dependent characteristics were analyzed by the NMR method. Finally, the correlation between water permeability and porosity in two environments was analyzed. Results show that water permeability coefficient of FA concrete both decreased with exposure time in two environments. FA can effectively improve the water impermeability, and the improvement effect increased with FA content in the later exposure period. Laboratory environment accelerated the decrease of water permeability and porosity. However, in the later stage, the decrease degree was not as good as that in the site environment. Pores with size of 10 to 100 nm occupy the main part of pores in FA concrete and the proportion of harmful pores of diameter 100 nm or larger decreased with exposure time. The water permeability coefficient and porosity of concrete exposed for 520 days in laboratory are close to that exposed for 800 to 1000 days in site, showing a good time dependent correlation in both environments, and the correlation with exposure time is stronger than that considering FA content.