Unveiling the Steel–Concrete Interfacial Characteristics Influencing Chloride-Induced Corrosion Initiation Using X-ray Computed Tomography

Chloride-induced corrosion is one of the most critical forms of degradation in reinforced concrete (RC). In Western European countries, where many buildings and infrastructures are approaching (or even exceeding) the end of their designed service life, the demand for maintenance, repair, and eventual demolition or reconstruction continues to grow. There is an urgent need for reliable service life models that can accurately predict when maintenance or the end of a structure's serviceability and safety will occur. Such models would enable targeting the needed maintenance interventions, optimizing the use of resources, and help reducing the environmental footprint associated with cement production. To develop these models, a deep understanding of the fundamental processes driving chloride-induced corrosion in RC is essential. Among others, recent studies suggest that heterogeneities at the steel-concrete interface (SCI), particularly macro voids, play a crucial role in initiating corrosion. The moisture content at the SCI, along with the moisture conditions and air-liquid configuration within the interfacial air voids, appears to drive the onset of corrosion. Furthermore, the presence of a thin (few micrometers) cement paste layer between the steel and air voids at the SCI may also influence how moisture ingress occurs in void volumes and, also, the favorable air-liquid configuration therein. To assess the impact of this air-liquid configuration on chloride-induced corrosion initiation, X-ray computed tomography (XCT) has been employed in this study. XCT is an ideal tool for this investigation due to its non-destructive nature, allowing for the study of corrosion mechanisms in an undisturbed state over time. Additionally, XCT can resolve moisture within concrete air voids, providing valuable insight into the corrosion process. The goal of this study is to elucidate the influence of SCI characteristics, specifically macro voids and their internal air-liquid distribution, on the complex, coupled processes leading to the initiation of chloride-induced corrosion in steel embedded in concrete thanks to XCT.