## 3 Results
### Internal Cracks at the Steel/Concrete Interface  
In order to obtain a realistic view of the degradation state of corroded structural elements, it is essential to conduct an accurate assessment of the internal crack patterns. Despite the absence of visible indications on the surface of the concrete, this degradation has a significant influence on the service life of RC structural elements. Different internal crack patterns were observed in slices T10 to T17. Three main directions of cracks were observed: vertical (V), horizontal (H and H') and oblique (O and O') (Table 4). The apostrophe \(\propto\) '\(\approx\) represents the occurrence of a second crack. Table 4 illustrates a selection of representative internal crack patterns observed. Tables 5-7 summarise the average and standard deviation (in italics) for the 16 samples per prism based on the three impressed current densities of 50, 100, and 200 \(\mu\)A/cm\({}^{2}\). Table 5 indicates that crack H was consistently present in all the slices of the studied RC prisms, followed by the occurrence of crack V. Crack O exclusively occurred at a total charge of 336 A.h/m\({}^{2}\) and current densities of 100 and 200 \(\mu\)A/cm\({}^{2}\). Crack O' only appeared at the highest current density (200 \(\mu\)A/cm\({}^{2}\)) and total charge (840 A.h/m\({}^{2}\)). Crack H' was only observed for a total charge of 840 A.h/m\({}^{2}\) (at the current densities of 50 and 200 \(\mu\)A/cm\({}^{2}\)). Cracks O, O' and H' only occurred when a significant total charge was achieved (336 or 840 A.h/m\({}^{2}\)). Regarding Table 6, the maximum duration of the accelerated corrosion tests conducted for all current densities, resulted in the formation of cracks H and V reaching the surface of the concrete. The propagation of cracks through the concrete cover was more easily observable when the cover was thinner (30 mm in comparison to the 50 and 75 mm concrete covers on the other faces). The remaining cracks (H', O and O') never run through the entire concrete cover. This observation is in accordance with the findings reported by [7, 18, 20, 22, 25, 26, 33, 38, 56, 60, 61, 62, 63, 64]. Table 7 illustrates that the crack width increased for all cracks and current densities, with the exception of crack H with current densities of 50 and 200 \(\mu\)A/cm\({}^{2}\). This can be attributed to the occurrence of crack H'. Indeed, the evolution of the width of the first cracks can be explained by the posterior development of new cracks that may be formed depending on the current density and the test duration. However, the sum of the crack widths at each total charge reveals an increase with the duration of the accelerated corrosion test for all current densities used. \begin{table}
\begin{tabular}{c c c} \hline  & **Total Charge (A.h/m\({}^{2}\))** \\ \hline Current density & 168 & 336 & 840 \\ (\(\mu\)A/cm\({}^{2}\)) & & \\ \hline P23-14d-T12R & P25-28d-T16R & P27-70d-T14R \\ \hline P31-7d-T11R & P05-14d-T10R & P11-35d-T11R \\ \hline P14-3.5d-T11R & P16-7d-T16R & P17-17.5d-T13R \\ \hline \end{tabular}
\end{table} 
Table 4: Examples of internal crack patterns (where Pn-Xd-TiR represents the right face of the slice Pn-Xd-Ti). Additionally, the results presented in Tables 4-7 also show (i) an increase in the orientation, length and width of internal crack patterns in conjunction with the increase of the total charge, and (ii) that for a chosen total charge, the internal crack pattern was more developed for higher values of current density. The differences in the observed crack patterns can be attributed to two factors: (i) the heterogeneity of the concrete (in terms of aggregate size and shape in proximity to the rebar, and the presence of voids) and (ii) the non-uniform distribution of the corrosion products, which exhibited varying ranges of thickness around and along the steel rebar. Few researchers have worked on the analysis of internal crack patterns due to corrosion induced by an impressed current mode.