Investigation on the Air Permeability and Pore Structure of Concrete Subjected to Carbonation under Compressive Stress

Concrete structures have to withstand the combined effects of external load and environmental factors. Therefore, it is meaningful to study the durability of concrete under compression and carbonation. The air permeability coefficient (k(Au)) and pore structure of concrete under uniaxial compression and carbonation were measured by the Autoclam method and mercury intrusion porosimetry (MIP). The Autoclam test results showed that the concrete k(Au) changed in a concave parabolic manner with the compressive stress level, and the inflection point of the stress level was 45%. The MIP results showed that the characteristic pore structural parameters (porosity, average pore diameter, median pore diameter by area, and median pore diameter by volume) first decreased and then increased with the stress level change. The change in concrete microstructure was a result of the combined effect of pore filling, decalcification, and densification, as well as the split effect. The key pore structural parameters affecting k(Au) were confirmed using gray relational analysis (GRA). The top three parameters with the highest correlation with the carbonated concrete k(Au) were porosity (gray relational grade γ(i) = 0.789), median pore diameter by volume (γ(i) = 0.763), and proportion of transition pore volume (γ(i) = 0.827). Furthermore, the regression analysis showed a good linear relation between k(Au) and the important pore structural parameters.