## 3 Results and Discussion  
### Characterization of Steel Reinforcement Passivation Based on Open-Circuit Potential  
The passivation process of steel reinforcements in concrete is a crucial aspect of corrosion protection as it aims to reduce the exposure of the steel to corrosive agents, such as water and oxygen, and enhance the longevity of the structure. This electrochemical process involves the movement of ions in the electrolyte surrounding the steel reinforcements in the same direction, effectively making the entire structure behave as an electrical conductor. Electrochemical testing is a commonly used method to quantitatively measure the corrosion status of steel reinforcements, primarily by assessing the current intensity on the surface  
Figure 2: The electrochemical testing system and methods.  
of these steels. The OCP test is one of the key electrochemical tests for a more qualitative assessment of the corrosion behavior and corrosion protection of steel in a given environment because the potential value is influenced not only by the anodic process (passivation) but also by the cathodic depolarization reaction. In this study, OCP measurements were taken on the working electrode, which was a HRB400 steel reinforcement, in a simulated concrete solution. The results of this test are presented in Figure 3.  
Figure 3 clearly shows that the OCP variation of the steel electrode in the concrete simulation solution is noteworthy. As the soaking test time increases, the OCP gradually increases and stabilizes after 5 days. This trend indicates that the steel electrode transitions from an active state to a passive state in the simulated liquid environment of concrete. At 0 days, the OCP of the steel electrode is \(-310\) mV. From the fifth day onwards, the amplitude of the OCP stabilizes at \(-140\) mV and tends to remain constant. The OCP observation with time suggests that the steel reinforcement develops a protective passive film that reduces its tendency to corrode. This passive film is believed to be primarily composed of corrosion products such as iron oxides and/or surface deposits (such as CaCO\({}_{3}\) or calcium oxide CaFe\({}_{2}\)O\({}_{4}\), etc.). The gradual stabilization of the OCP after 5 days indicates that a relatively stable and protective passive film was formed on the steel surface, reducing its exposure to corrosive agents. Furthermore, it can also be inferred from Figure 3 that there is a correlation between the soaking time and the potential increment of adjacent days. As time progresses, the potential increment of adjacent days gradually decreases, indicating that the steel electrode transitions from an active state to a passive state in the simulated liquid environment of concrete. This observation supports the notion that a protective passive film forms on the steel surface with increasing time. Taken together, these results provide valuable insights into the passivation process of steel reinforcements in concrete. Specifically, they suggest that after an initial passivation period (0-5 days), the steel reinforcement enters a passive state where a protective film forms on its surface, significantly reducing its tendency to corrode. These findings have important implications for optimizing corrosion protection strategies for steel reinforcements in concrete structures. For example, coating protection methods can be used, such as applying anticorrosion coatings, to enhance the protective effect of the oxide film to a certain extent.  
Figure 3: The variation law of the OCP during the passivation process of steel reinforcements in concrete.