# Monitoring of Reinforced Concrete Corrosion: Active and Passive Bars Exposed to Climate
## 4 Discussion
Corrosion rate monitoring enables the real-time estimation of reinforcement section loss by calculating the corrosion depth, \(P_{corr}\)[23], which is related to the loss of radius through [PERSON]'s law (see Equation (1)). This allows for the calculation of section loss of reinforcement in a structure in real-time by integrating the corrosion rate curve. The acquisition of this parameter can be integrated into the mechanical behaviour model either on a punctual or continuous basis (digital twin), thereby enabling the automatic evaluation of the structure's safety. \[P_{corr}(t)=\int_{t=0}^{t}\left(\alpha\ i_{corr}(\tau)\ M_{Fe}\left/(n\ d\ F)\right)\ d\tau\right. \tag{1}\]  
Here, \(\alpha\) is the pitting factor, \(M_{Fe}\) is the atomic mass of iron, \(n\) is the number of electrons for anodic reactions, \(d\) is the mass density of steel, and \(F\) is the Faraday's constant. Reinforced concrete structures may be affected by various corrosion mechanisms, including general corrosion, pitting, and stress corrosion cracking. Each mechanism induces a different mechanical behaviour, which can lead to macroscopic embrittlement [7; 14; 16; 48]. While microscopic behaviour may be ductile in general and pitting corrosion, it may become brittle or quasi-brittle under stress corrosion cracking due to environment-mediated microstructural embrittlement. Hydrogen embrittlement (HE) is a phenomenon that can occur in conjunction with corrosion or stress corrosion and is considered a leading cause of structural steel cracking under stress. Studies on interstitial hydrogen in the iron network have shown that its primary effect is not due to the establishment of chemical bonds with iron atoms but rather the introduction of internal stresses that weaken the interactions between iron atoms, ultimately reducing fracture toughness [15; 49; 50; 51; 52; 53]. Several studies have shown that fracture toughness (KIC) decreases when cracks form and propagate in aggressive, particularly corrosive environments. This decrease in fracture toughness means that the material fails at much smaller crack sizes under any given level of tensile stress. Brittle failure occurs with the onset of cleavage facets on a microscopic scale. The primary cause of this type of failure is hydrogen embrittlement. Based on experimental findings, it has been observed that hydrogen can reduce fracture toughness to approximately 60% of its value in an inert environment. There are two types of embrittlement: macroscopic brittleness induced by the notch effect, in which the steel remains ductile, and microscopic embrittlement due to hydrogen uptake in the iron lattice, resulting in the appearance of quasi-cleavage facets and a decrease in plastic deformation. Figure 12: Corrosion rate monitoring (green-red shaded curve) together with relative humidity (black dotted curve) and rainfall (blue shaded curve). Figure 13 shows an example of a calculation for the depth of reinforcement corrosion and its corresponding linear fit. A linear fit has been used to estimate the corrosion evolution, which may vary depending on the environment and years of exposure. Fitting corrosion occurs in the presence of chlorides, and the pitting factor, \(\alpha\), must be considered. The pitting factor is the ratio between the maximum pitting size and the generalised corrosion. It allows for the calculation of the critical section loss in the reinforcement and takes values between 3 and 20 [10; 39; 54; 55]. Assuming a pitting factor of 10 and that the recorded period is representative, the corrosion evolution can be estimated, and intervention on the beam can be planned. The estimated annual corrosion loss in the chloride-free zone of the beam is 0.20 \(\upmu\)m, while in the chloride-contaminated zone, it is 7.6 \(\upmu\)m. Therefore, if the durability limit state is set at 50 \(\upmu\)m [56], the chloride-contaminated zone would reach this limit state in approximately 6.6 years, whereas the chloride-free part has a life of over 200 years.