Effect of pore structure on gas diffusion in fly ash concrete

Abstract：The effect of using fly ash to replace cement on concrete pore size distribution was studied by mercury intrusion porosimetry. The gas diffusion mechanism in concrete and test re- sults was used to estimate the effect of fly ash replacement on 02 and CO2 diffusion in fly ash concrete. The test results provide the total porosity of the concrete, the porosity broken down into harmful and more harmful hole （~50 nm） sizes, the most probable pore size, and the av- erage pore diameter. These values are significantly increased when fly ash replacement of ce- ment in the concrete is 45%. The type of gas diffusion through most porosity （more than 80~） in ordinary concrete, and in fly ash concrete, is transition diffusion. The diffusion of CO2 in fly ash concrete is greater than 02 diffusion for the same conditions. A 45~ fly ash re- placement increases the effective gas diffusion coefficient by less than 10~ because the ratio of sub-porosity in the transition zone and total porosity is less influenced by fly ash replacement.