## 3 Results
### External Cracks  
External cracks are the key point in an investigation to identify the degradation of an RC structure suffering from corrosion. In this study, external cracks were characterized by means of visual inspections and crack widths (Figure 10 and Table 8). Figure 10: Maximum width of external cracks in RC prisms using different impressed current densities. (**a**) 50 \(\mu\)A/cm\({}^{2}\), (**b**) 100 \(\mu\)A/cm\({}^{2}\) and (**c**) 200 \(\mu\)A/cm\({}^{2}\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**RC Specim** & **Top Face (T)** & **Front Face (F)** & **Corrosion Test** & **Impressed Current** \\
**Name** & **Top Face (T)** & **Front Face (F)** & **Duration (Days)** & **Density (\(\mu\)A/cm\({}^{2}\))** \\ \hline P21-5d-50 & & & & \\ P22-5d-50 & & & & \\ P23*-14d-50 & & & & \\ P24-14d-50 & & & & \\ P25*-28d-50 & & & & \\ P26-28d-50 & & & & \\ P27*-70d-50 & & & & \\ P28-70d-50 & & & & \\ P29-79d-50 & & & & \\ P30-79d-50 & & & & \\ P31*-7d-100 & & & & \\ P32-7d-100 & & & & \\ P05*-4d-100 & & & & \\ P06-14d-100 & & & & \\ P07-21d-100 & & & & \\ P08*-21d-100 & & & & \\ P09*-28d-100 & & & & \\ P10-28d-100 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Pictures of external crack patterns of RC prisms using different impressed current densities (50, 100 and 200 \(\mu\)A/cm\({}^{2}\)). (* asterisk indicates the prism used for physical characterizations; total charge values in bold print are those that can be found in all series). From the visual observations of the RC prisms after the accelerated corrosion test, concrete deteriorations were easily observed on T and F faces, which are those closest to the steel rebar. No deterioration was observed on the other faces. The following four types of external crack pattern induced by corrosion (Figure 10 and Table 8) were identified on the RC prisms:  
* Crack pattern 1: A single longitudinal crack formed on the front face with a maximum width range of between 0.1 and 0.7 mm. This crack pattern was observed for the three current densities. The width of the crack increased with the duration of the corrosion test;
* Crack pattern 2: A single longitudinal crack formed on the top face with a maximum width of between 0.2 and 0.3 mm. This crack pattern was observed exclusively for a current density of 100 \(\mu\)A/cm\({}^{2}\) and durations of 7, 14 and 35 days;
* In crack patterns 3 and 4, two longitudinal cracks formed on the front face as well as on the top face (with increasing duration of the accelerated corrosion test). The difference between these patterns was the appearance of the first crack, on the front face for crack pattern 3 and on the top face for crack pattern 4. The initiation of the crack took place in the middle section of the PVC tank, and the propagation of the crack followed the rebar until the cracks reached the two extremities of the RC prism. However, a more detailed observation reveals the opposite for RC prisms P12 and \begin{table}
\begin{tabular}{c c c c} \hline \hline
**RC Specim** & **Top Face (T)** & **Front Face (F)** & **Corrosion Test** & **Impressed Current** \\
**Name** & & & **Duration (Days)** & **Density (\(\mu\)A/cm\({}^{2}\))** \\ \hline P11*-35d-100 & & & 35 & 100 \\ P12-35d-100 & & & 35 & 200 \\ P13-3.5d-200 & & & 3.5 & 200 \\ P14*-3.5d-200 & & & 7 & 200 \\ P15-7d-200 & & & 17.5 & 200 \\ P16*-7d-200 & & & 19.5 & 200 \\ P17*-17.5d-200 & & & 17.5 & 200 \\ P18-17.5d-200 & & & 19.5 & 200 \\ P19-19.5d-200 & & & 19.5 & 200 \\ P20-19.5d-200 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: _Cont._P32, where the crack occurred at the extremities. It is important to mention that such crack occurrence is possible. * Regrettably, it was not possible to determine the precise timing at which the crack on the top face occurred (i.e., before or after the onset of the crack at the front face) due to the location of the PVC tank. Consequently, crack pattern 3 is assumed for a RC prism with two cracks when the front face crack was wider than the top face crack at the end of the corrosion test.