Effects of various inlet-gas mediums on apparent permeability of concrete under steady-state flow: Comparison between carbon-dioxide and oxygen

Apparent gas-permeability (k(a)) of concrete highly depends on pore-structure and medium. However, the effects of gas-medium on permeability have yet been investigated in depth. In this work, concrete with various water-to cement ratios and fly-ash/slag dosages is prepared for k(a) testing. Various gas-mediums (CO2 and O-2) are applied for analyzing their effects on the k(a). Meanwhile, pore-structure characteristic, inner gas-pressure, and gas absorption in concrete are observed for exploring permeation mechanism. The results illustrate that the narrowing pore-scale effect and surface-diffusion contribution derived from gas-absorption of CO2 and O-2 both have minor impacts on the k(a). The k(a) of O-2 (k(O2)) is higher than that of CO2 (k(CO2)) and their relative permeability (k(O2)/k(CO2)) ranges from 1.18 to 2.29. These deviations are mainly caused by significantly different Knudson diffusion occurring in the area near the concrete outlet-gas side (approximately 5%).