## 4 Discussion
### Tentative Explanations of the Evolution of Corrosion-Induced Cracking  
The preceding experimental results from both the published literature and our study show a notable dispersion and contrast in the data. This could be due to the large variety of parameters involved, such as the geometry of the prism, the geometry of the accelerated corrosion test setup, the test duration and the impressed current density. Figure 13 provides a preliminary illustration of the potential stages of the corrosion process from internal to external. The experimental observations indicate that the stresses generated by the corrosion products in the concrete surrounding the corner steel rebar lead mainly to the appearance of top and front face cracks. This corrosion-induced behaviour of RC prisms can be attributed  
Figure 12: Evolution of external crack widths from this work and from the literature [17; 19; 20]. Figure 13: Evolution of internal cracking leading to external crack patterns 1 and 3; (**a**) current phenomenon during the corrosion process; (**b**) occurrence of the first crack H; (**c**) occurrence of the second crack V.  
to two factors: (i) the location of the steel rebar near these two faces and (ii) the location of the PVC tank, which generates a vertical water and chloride ion content gradient in the concrete cover. Indeed, it can be stated that the most significant generating current lines are located between a part of the circumference of the steel rebar (specifically the upper-front section) and the top face of the prism. Since the rebar was located in the RC prism corner, the current lines generated around the rebar are unequally distributed. In addition, the concrete heterogeneity and the numerous phenomena occurring during the accelerated corrosion test (such as the dissolution/diffusion/precipitation of iron in the concrete pores and cracks, the oxygen content and gradients of humidity and of chloride ions), result in the generation of sloping pressures due to the corrosion products that are formed mainly in the upper-front section (between C8 and C3). These pressures therefore promote the formation of a shear crack in the concrete cover, which mainly manifests as an H crack and a V crack, as presented in Figure 13. But due to the non-uniform accumulation of the corrosion products, a delay in occurrence between these two cracks is observed. One may note that the H crack is the most common (64.3%), occurring first to due to the superior supply of oxygen to the steel surface facing to the front face [57]. This facilitates the formation process of corrosion products, which in turn leads to cracking of the concrete cover [57]. This crack evolution can then be schematically presented in Figure 13.  
In light of the aforementioned findings, it can be concluded that the order of appearance of cracks is complex to predict. The unequal development and distribution of the corrosion products exert an influence on the formation of the cracks. In the course of this present study, a total of sixty-five papers were reviewed. Of these, only four have investigated the internal degradation of RC elements, particularly in direct relation to the morphology and distribution of corrosion products [16; 30; 37; 65]. However, it is essential to correctly determine the distribution of corrosion products in order to provide an adequate assessment of the internal and external crack patterns. As previously stated in the literature, the thickness of the corrosion layer around the steel rebar is generally determined by the depth of the corrosion damage to the steel rebar, either from the rebar section loss or from the rebar mass loss. However, the results obtained by researchers such as [34; 66; 67; 68] indicate that the direct determination of the corrosion layer thickness through SEM/EDS analysis is a more realistic approach to reach this goal. This is why our investigation has focused on the experimental determination of the distribution of corrosion products around the steel rebar through direct observations. In their work, refs.