# Time-Dependency in the Corrosion Process of Reinforced Concrete Subjected to a Chloride Solution
## 4 Results and Discussion
### Electrical Parameters in Galvanostatic Pulse Technique  
Steel bars in concrete subjected to chloride-induced corrosive environments were monitored using the GP technique. The fitting was performed using Equation (1) using the Levenberg-Marquardt algorithm coded in Matlab(r) (R2022a). Figure 4 shows the ohmic resistance with respect to time. The measured values are depicted as an average value with a one standard deviation error bar, which sometimes appears to be absent owing to the relatively large markers. The ohmic resistance for both samples continuously increased within the measurement duration; from 177.6 \(\Omega\) to 303.2 \(\Omega\) for 0.4 OPC and from 108.5 \(\Omega\) to 131.0 \(\Omega\) for 0.6 OPC. The results showed that hydration in the cement matrix had proceeded to a great extent for both concretes. The hydration process of concrete with a lower w/c was expected to be terminated owing to less free water for the process in the concrete; however, this was not observed. This appeared to be caused by the rapid loss of free water in the 0.6 OPC concrete during the drying phase and additional pore refinements by chloride binding in the 0.4 OPC concrete. Overall, the ohmic resistance of the 0.4 OPC concrete was 87.8% higher than that of the 0.6 OPC concrete, and no corrosion of steel in the 0.4 OPC concrete was detected. Therefore, a higher ohmic resistance indicated a higher corrosion resistance owing to less connectivity of the pore structure, resulting in the lower permeability of aggressive agents, such as chloride. Figure 4: Ohmic resistance with time using GP technique. Figures 5 and 6 show the capacitance and polarisation resistance of steel which account for its characteristics, and the plots are depicted for each steel rather than the average value. For the capacitance, the values in the low-w/c concrete, ranging from 10 mF to 15 mF, were generally lower than those in the high-w/c concrete, with values up to 130 mF. The expected causes are explained as below. (1) More uniform types of passive film are formed on steel embedded in the low-w/c concrete [27; 28], or a layer of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\), comprising the outer products in the passive film and having a lower dielectric constant, thickens through the transformation of magnetite, which is the main inner product in the passive film [29; 30]. Thus, a uniformly distributed passive film on the steel may provide a higher corrosion resistance, such as that in a well-coated steel. However, a higher capacitance indicates a higher roughness on the steel, such as that in a poorly coated steel. (2) Chlorides reached the steel depth during the measurement. Thus, higher values resulted in degpassivation caused by chloride, resulting from an increase in the steel roughness. The tendency for an increase in the capacitance of the corroded steel was consistent with that found in previous studies [31; 32]. Figure 6 shows that polarisation resistances were significantly high, with values up to 20 k\(\Omega\) for all samples, irrespective of exposure time for the passive state. After depassivation, the polarisation resistance of steel decreased significantly. In addition, corrosion propagation was maintained owing to the continuous decrease in the polarisation resistance. Before the aggressive agents reached the appropriate steel depth, electrochemical conditions in the steel were stable owing to the presence of a protective layer on the steel surface, such as a passive film comprising \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) with low conductivity. The corrosion rate with only oxygen and moisture under high-alkalinity conditions was extremely slow without a catalyst, such as chlorides; thus, it was negligible in this phase. Consequently, the values of both parameters changed significantly after the transition phase; that is, the depassivation process.