## 3 Results and Discussion
### Corrosion-Induced Concrete Cracking  
Table 4 shows the amount of transverse and longitudinal bar corrosion when the first corrosion cracking was observed at the surface of the specimens. Three transverse bars were embedded within the specimens, although all cracks occurred in the bars that were placed at the top or bottom of the  
Figure 4: Comparison of calculated and experimentally determined rebar weight loss.  
Figure 3: Comparison of weight losses between corner and intermediate bars.  
specimens. In the case of the longitudinal bars, cracking was observed only around the corner bars. As such, the cracking in association with the transverse bars is divided into 'top' and 'bottom' in Table 4.  
Corrosion cracking at the surface of the D32-Fc24-C40 and D32-Fc48-C20 specimens was first observed three days after the tests began. These specimens had the lowest compressive strength and thinnest concrete cover, respectively. In all specimens except D32-Fc48-C60, which had the thickest concrete cover, cracks occurred in the transverse bar before they occurred in the longitudinal bar. Corrosion cracking occurred first in the transverse bar (top) of D32-Fc24-C40, which was likely due to the bleeding that occurred in association with a large number of pores that formed in the hardened cement due to its high W/C ratio. According to [PERSON] [19], the pores expand due to bleeding during the mixing of concrete with a high water/cement ratio, and this causes the concrete density to vary according to the specimen's height. Indeed, it was found that taller specimens tend to show evidence of accelerated rebar corrosion. On the other hand, when the compressive strength of concrete is high, the effect of bleeding is reduced. Therefore, corrosion cracking occurred in the lower transverse bars of specimen D32-Fc48-C40 and D32-Fc72-C40.  
Figure 5 shows the amount of rebar corrosion at the point at which corrosion cracks reached the surface of RC specimens. This was lowest in D32-Fc24-C40 and highest in D32-Fc48-C40, and also tended to be higher in specimens with higher compressive strengths, although corrosion was less in D32-Fc72-C40 than D32-Fc48-C40 (Figure 5). Concrete with a high compressive strength has a correspondingly high tensile strength and, as such, its resistance to tensile cracking is enhanced. However, the density and volume of cement paste pores also tend to be lower in high-strength concrete [15] and, as such, the amount of corrosion product that is absorbed by pores is reduced and the corresponding expansion pressure in the surrounding concrete increases. Therefore, there is an increased possibility that corrosion cracks will form in high-strength concrete in response to a relatively low amount of corrosion. [4; 10; 20] Because of this, the amount of rebar corrosion at the point at which surface cracking occurred was lower in specimen D32-Fc72-C40 than in D32-Fc48-C40, despite the former having the highest compressive strength.  
The amount of rebar corrosion at the point at which cracks reached the surfaces of specimens notably increased as the cover thickness increased. In Figure 6, the amount of rebar corrosion at the time of surface cracking increases by a factor of two when the cover thickness is increased by 20 mm. [PERSON] et al. [21] also found a linear relationship between concrete cover thickness and rebar corrosion expansion pressure, which is attributed to more strain energy being required to create cracks in concrete with a thicker cover.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Specimen ID**} & \multicolumn{2}{c}{**Corrosion Rate (mg/cm\({}^{2}\))**} \\  & **Longitudinal Bar** & **Transverse Bar (Crack Location)** \\ \hline F20-D32-C40 & 17 & 14 (top) \\ F40-D32-C40 & 46 & 38 (bottom) \\ F60-D32-C40 & 23 & 28 (bottom) \\ F40-D38-C40 & 17 & 61(top) \\ F40-D25-C40 & 33 & 49 (bottom) \\ F40-D32-C20 & 18 & 18 (top) \\ F40-D32-C60 & 23 & 75 (top) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Corrosion rate and crack width at the time of the first cracking.