An enhanced air permeability model based on stable moisture conditions for nondestructive durability assessment

Abstract Concrete carbonation resistance is essential for ensuring durability and extending the service life of concrete structures, as carbonation can lead to the degradation of reinforcing steel and compromised structural integrity. Accurately assessing carbonation resistance through in situ measurements is crucial for evaluating and mitigating potential durability risks over time. Therefore, this study proposes a simple and accurate model for the nondestructive evaluation of concrete carbonation rates under natural conditions. The Torrent air permeability method was applied to measure the changes in the air permeability coefficient, kT , of concrete specimens produced using various cement types, water-to-binder ratios, and initial curing times. The permeability of the concrete, when equilibrated with external environmental conditions, kT e , was predicted based on early-age measurements of kT to determine the concrete carbonation rate, kC . The results indicated that the kT e index achieved a mean ratio between predicted and measured kC values of 1.032, with a low standard deviation of 0.264 and a CoV of 25.5%, indicating high consistency and accuracy compared to conventional air permeability indices. Thus, the proposed method can be applied to effectively predict the carbonation rate under natural exposure conditions, using only early age air permeability measurements.