Research On Influence Factors Of Gas Permeability Coefficient Of Concrete

Permeability is an important index for evaluating the durability of concrete. In this paper, electric flux and gas permeability coefficient of concrete were experimentally discussed. The effect of gas pressure, test time, specimen pretreatment, water binder ratio, Class I fly ash, carbonization, curing way, wet-dry cycles and compressive strength on gas permeability was studied using the self-made apparatus.The results show that test time has little influence on gas permeability coefficient and the reasonable test pressure interval is controlled in the range of 250~300KPa. Specimen pretreatment has a great effect on gas permeability coefficient. In this study, the specimens are dried for 2 hours in an oven at the temperature of 105℃, then are sealed after polished.Class I fly ash has a great effect on gas permeability coefficient. When the cement is replaced by Class I fly ash at the content of 40%, compared with the reference concrete, the gas permeability coefficient decreases by 9%, 14.7% and 13.4% at 28 days, 56days and 90days, respectively. The gas permeability coefficient decreases with the increasing of carbonization time. Concrete cured in standard condition and dry environment have different gas permeability coefficients, which in standard condition is 32.8% higher than that in dry environment. Different frequencies of wet-dry cycles have different gas permeability coefficients in concrete. The higher the frequency, the lower gas permeability coefficients become. For different water binder ratio, the relationship between compressive strength and gas permeability show linear correlation.Four different fitting methods are used to evaluate the quantitative relationship between electric flux and gas permeability coefficient under different water binder ratio in this study. It is found that piecewise linear fitting method can be used to exactly characterize the quantitative relationship.