## 3 Results and Discussion
### Crack Widths According to the Corrosion of Transverse Bar  
The longitudinal bar corroded less than the transverse bar, although some of the corrosion by-products flowed out towards the concrete surface through the transverse bar corrosion cracks that formed during the early stages of the test. Because of this, the influence of longitudinal bar corrosion on the growth of corrosion cracks was relatively small. Figure 10 shows the relationship between the amount of corrosion and crack width at the transverse bar, which is where the largest surface cracks were observed. Because the widths of transverse bar corrosion cracks were influenced by the products that occurred at the longitudinal bar, larger crack widths may be recorded than would be the case in tests employing unidirectional rebar. The crack width in all specimens showed a tendency to increase with 20-70 mg/cm\({}^{2}\) of corrosion, which is the range at which corrosion cracking occurs. However, at crack widths of \(>\)0.2 mm, the ratio of crack width increase tended to be lower because an increased amount of corrosion product could flow out through these cracks.  
Figure 9: Crack patterns at the final stages of corrosion testing.  
The effects of concrete compressive strength are shown by comparing specimens F20-D32-C40, F40-D32-C40, and F60-D32-C40. In specimen D32-Fc24-C40, which had the lowest compressive strength, the changes in crack width were limited up to 200 mg/cm\({}^{2}\) of corrosion. This was likely due to a higher density of pores in the cement paste due to the higher water:cement ratio, into which rebar corrosion by-products diffused and were accommodated. In contrast, as seen in specimens D32-Fc48-C40 and D32-Fc72-C40, the cement paste of higher-strength concrete will have fewer pores and, as such, rebar corrosion by-products become concentrated at the crack surfaces. As a result, crack width rapidly increased in the higher strength concrete, even when the amount of corrosion was relatively low.  
In the comparison between specimens with different concrete cover thicknesses (F40-D32-C20, F40-D32-C40, and F40-D32-C60), specimen D32-Fc48-C20, which had a thin cover, showed an increase in crack width at a smaller amount of corrosion. However, after cracking had occurred, corrosion by-products could easily flow out via the cracks in the concrete cover. Therefore, at 50 mg/cm\({}^{2}\) of corrosion, the increase in crack width was lower than in specimen D32-Fc48-C40, which has a thicker cover. In the specimen with the thickest cover (D32-Fc48-C60), the fracturing energy required to create surface cracks would have been higher, meaning that more corrosion was required to initiate cracking (100 mg/cm\({}^{2}\)), after which crack width increased rapidly (Figure 5). According to the previous study [22], it was investigated that the cover depth had a greater effect on the durability of RC than the crack width.  
For the specimens with different longitudinal bar diameters and numbers (F40-D25-C40, F40-D32-C40, and F40-D38-C40), the relationship between rebar corrosion and crack width was less distinct. This is unsurprising considering that these specimens had the same compressive strength (Fc48), cover thickness (40 mm), and transverse bar diameter (D16), and their longitudinal bar reinforcement ratios were similar. As such, the reinforcement ratio is considered to have a greater effect on the relationship between the amount of transverse bar corrosion and crack width than differences in the longitudinal bar diameter.