## 3 Results and Discussion
### Corrosion Current Density (\(i_{\text{corr}}\))
#### 3.2.2 \(i_{\mathrm{corr}}\)  
Galvanized Steel and AISI 1018 Carbon Steel in Concrete Exposed to 3.5 wt.% MgSO\({}_{4}\) Solution  
Figure 7 shows the \(i_{\mathrm{corr}}\) transient response of the CS and GS reinforcements embedded in CC, BSC1 and BSC2 exposed to 3.5 wt.% MgSO\({}_{4}\) solution. Specimens reinforced with CS, CC-MS-CS, BSC1-MS-CS and BSC2-MS-CS, present a behavior very similar to those reported in the reference specimens exposed to the control media during the curing stage, with \(i_{\mathrm{corr}}\) values between 0.38 and 0.34 uA/cm\({}^{2}\), reaching values of \(i_{\mathrm{corr}}\) between 0.32 and 0.25 uA/cm\({}^{2}\) on day 28. This is associated with the formation of the passive layer. When the specimen is exposed to the aggressive environment, the \(i_{\mathrm{corr}}\) values show a decreasing tendency, with values below 0.10 uA/cm\({}^{2}\) on day 84, indicating a negligible level of corrosion in this moment. This behavior agrees with the literature, where a favorable behavior against corrosion occurs in the first months of exposure to sulfated media [101]. However, after day 126 of exposure, there is an increasing trend in the \(i_{\mathrm{corr}}\) values for the three specimens, CC-MS-CS, BSC1-MS-CS and BSC2-MS-CS, which agrees with the \(E_{\mathrm{corr}}\) values reported for specimens, which can be associated with the activation of the system. This activation is achieved on day 168 when the three specimens presented values greater than 0.10 uA/cm\({}^{2}\), remaining between 0.13 and 0.09 uA/cm\({}^{2}\), until day 252, where there is a greater increase in corrosion rate, reaching values of \(i_{\mathrm{corr}}\) at the end of the monitoring of 0.24, 0.22 and 0.18 uA/cm\({}^{2}\), respectively. This indicates that in the exposure conditions of the present study, the CS reinforced BSC1 and BSC2 specimens impart a higher corrosion protection than CC, this favorable behavior coinciding with the use of SCBA and SF in sulfate media as reported in the literature [102]. Figure 7: \(i_{\mathrm{corr}}\) monitoring of GS and CS reinforced concrete exposed to 3.5 wt.% MgSO\({}_{4}\) solution. The specimens with GS, CC-MS-GS, BSC1-MS-GS and BSC2-MS-GS also presented a behavior very similar to that analyzed in the specimens exposed to the control medium (DI-water) in the curing stage. Showing \(i_{\mathrm{corr}}\) values between 0.28 and 0.22 \(\mu\)A/cm\({}^{2}\), at the beginning of the curing stage and reaching values of \(i_{\mathrm{corr}}\) between 0.16 and 0.11 \(\mu\)A/cm\({}^{2}\) on day 28. A decreasing tendency is observed in the corrosion kinetics, maintaining values of \(i_{\mathrm{corr}}\) between 0.07 and 0.04 \(\mu\)A/cm\({}^{2}\), from day 56 to day 168. Thus indicating a better performance than the specimens reinforced with AISI 1018 CS, whose passivity breakdown occurred after day 126. The activation of steel for the specimens with GS is observed on day 182 with a constant increase, although still with \(i_{\mathrm{corr}}\) values below 0.10 \(\mu\)A/cm\({}^{2}\), which indicates according to Table 9 that the level of corrosion is negligible. However, for the CC-MS-GS specimen, made with conventional concrete (100% CPC), an \(i_{\mathrm{corr}}\) value above the passivation threshold is observed, showing an \(i_{\mathrm{corr}}\) value of 0.12 \(\mu\)A/cm\({}^{2}\), associated with a moderate level of corrosion. An increasing trend in the \(i_{\mathrm{corr}}\) values is observed, with an \(i_{\mathrm{corr}}\) value of 0.16 \(\mu\)A/cm\({}^{2}\). In the case of specimens made with BSC1 and BSC2, there is a greater resistance to corrosion induced by sulfates, presenting the specimen BSC1-MS-GS made with SCBA values until day 294 below 0.10 \(\mu\)A/cm\({}^{2}\). However, in the last monitoring, it reached a value slightly higher than 0.10 \(\mu\)A/cm\({}^{2}\), indicating the activation of the system but higher resistance than the CC-MS-GS specimen.