## 3 Results and Discussion
### Development of Corrosion-Induced Concrete Cracking  
Figure 7 shows the state of the specimen surfaces according to concrete compressive strength and cover thickness after approximately one month of accelerated corrosion testing. The same amount of voltage (10 V) was applied to all specimens, but the current was varied for each specimen and each rebar. As such, Table 5 shows the average corrosion amounts for the longitudinal and transverse bars that were calibrated using the integrated current amount. The amount of longitudinal and transverse bar corrosion tended to be lower when compressive strength was higher and when the cover was thicker. This likely reflects improved resistance to chloride ion permeation and, therefore, the hourly integrated current amount is reduced. Additionally, efflorescence, which is an indicator of concrete deterioration, was observed on the surfaces of specimens F60-D32-C40 and F40-D32-C60, both of which showed little corrosion and from which corrosion products did not flow out. However, for specimens F20-D32-C40 and F40-D32-C20, which experienced large amounts of (calibrated) corrosion, corrosion cracking occurred on their surfaces and a significant amount of rust flowed out through these cracks. Figure 5: Corrosion rate of steel rebar according to the compressive strength of concrete. Figure 6: Corrosion rate of steel rebar according to concrete cover depth. Figure 8 shows the surface cracks and the permeation of corrosion products after the accelerated corrosion tests were completed. Vertical cracks formed that were divided into concrete cover cracks and core cracks according to the position of the rebar (Figure 8a). Most corrosion products were observed in the vertically formed crack surfaces. After the concrete cover and rebar were separated, a diamond cutter was used on the core-side of the concrete to view the bottom of the section (Figure 8b). It was found that no cracks had formed due to rebar corrosion or corrosion by-product permeation in the core-side of the specimens. This indicates that the by-products from the corrosion of the longitudinal and transverse bars in the central portions of the specimens (where cracking did not occur) did not permeate toward the core but flowed out toward the surface through the cracks that formed in the upper and lower transverse bars. Figure 8: (**a**) Representative internal crack surfaces (**b**) corrosion product migration and (**c**) surface condition of the longitudinal bar after accelerated corrosion testing. Figure 7: Surface condition of RC specimens after 30 days of accelerated corrosion testing. Figure 8c shows a comparison of corrosion occurring on the inward- and outward-facing sides of the longitudinal bar (D38) of F40-D38-C40, with the other specimens showing similar patterns. Corrosion by-products can be seen on the outward-facing side (i.e., the side of the rebar facing the concrete cover) but not on the inward-facing side (i.e., the side of the rebar facing the specimen core). Therefore, in an environment where rebar corrosion progresses relatively rapidly, such as in the ocean, the effect of rebar corrosion on the core material of RC members may be relatively small. However, reductions in shear capacity may represent a risk due to increases in the transverse bar strain or member flexural strength associated with concrete cover peeling or a reduction in the rebar cross-section. Figure 9 shows the crack shape and maximum width for each specimen after the accelerated corrosion tests were completed. With the exception of specimen F20-D32-C60, in which corrosion cracking only occurred in association with the longitudinal bar, crack widths were greatest around the transverse bar placed at the top and bottom of the specimens. In comparison, there were few cracks around the longitudinal and transverse bar placed in the middle of the specimens.