## 3 Results and Discussion
### Corrosion Current Density of Reinforcement Steel  
The \(\mathrm{i_{corr}}\) results are presented in Figures 11 and 12, allowing comparison of the corrosion resistance of the steel-concrete systems under study. It can be seen from Figure 11 that the system with 20% RFA (RFA-20) and the reference system (NAT) exhibit a similar electrochemical behavior keeping at a moderate corrosion level (\(\mathrm{i_{corr}}\) values between 0.5 and 1.0 \(\mathrm{\SIUnitSymbolMicro A}/\mathrm{cm^{2}}\)) until the end of the exposure time and a low corrosion level (\(\mathrm{i_{corr}}\) values between 0.5 and 1.0 \(\mathrm{\SIUnitSymbolMicro A}/\mathrm{cm^{2}}\)) in the first weeks of exposure. In the systems with 30%, 60%, and 100% of RFA there is a significant increase of \(\mathrm{i_{corr}}\) from week 7, 11, and 12, respectively, (they changed from a low corrosion level to moderate).  
The corrosion risk limits shown in Figures 11 and 12 were established in a previous report [33].  
Figure 12 shows that systems with 20%, 30%, and 60% of RCA have an electrochemical behavior very similar to the reference system (NAT), maintaining at all times a level of corrosion between low and moderate (\(\mathrm{i_{corr}}\) lower than 1.0 \(\mathrm{\SIUnitSymbolMicro A}/\mathrm{cm^{2}}\)). Since the beginning of exposure time, the system RCA-100 shows higher values of the other systems, including in week 21 and 25 where it reached the high corrosion level, maintaining its \(\mathrm{i_{corr}}\) above the other RCA systems until the end of the evaluation period. In the system with 100% RA (RA-100), \(\mathrm{i_{corr}}\) increased significantly in week 13, reaching high values of corrosion (greater than 1.0 \(\mathrm{\SIUnitSymbolMicro A}/\mathrm{cm^{2}}\)); as of week 17, \(\mathrm{i_{corr}}\) maintained a very steep upward trend.  
In general, it can be noted in Figures 9-12 that \(\mathrm{\SIUnitSymbolMicro p}\) elucidates in a more clear way the effect of the RA in ionic conductivity of species in concrete because it is not susceptible to dissolved oxygen concentration, nor the surface state, type, and shape of the reinforcement steel oxides; which does not happen with \(\mathrm{i_{corr}}\) and therefore the variability of results in the first weeks and between the passive state systems.  
The results show that the more RA a concrete mixture contains, the higher the steel corrosion rate is. The presence of RA increases the porosity of concrete and increases the number of types of interfaces in the concrete, both of which make it easier for harmful materials such as chloride to penetrate the concrete. Thus, the higher the RA replacement percentage in RAC is, the higher the steel corrosion rate is. Also, the introduction of a low amount of RA (around 30% RCA or 20% RFA) does not increase the rate of steel corrosion significantly. In other publications [36; 37] similar results were found.  
In [36]\(\mathrm{i_{corr}}\) was measured under similar conditions (under humectation-drying cycles) and values and trends similar to those obtained in the present work were found. It can also be seen in this study that due to the resistive nature of the concrete, the sensitivity of the LPR technique and other variables, the standard deviation of the measurements is large (around 0.1 \(\mathrm{\SIUnitSymbolMicro A}/\mathrm{cm^{2}}\)). In the present work, slightly higher \(\mathrm{i_{corr}}\) values were obtained because during the drying period the specimens were exposed to 40 \({}^{\circ}\)C in an oven generating more extreme conditions (in [36], during the drying periods, the specimens were exposed to the air in the laboratory).