## 3 Design of Reinforced Concrete Corrosion Testing
### Analysis of the Corrosion Rate of Steel Reinforcements in Concrete and UHPC Short Columns  
The relationship between the duration of electrical corrosion and the corrosion rate for concrete and UHPC short columns is shown in Figure 10. The theoretical corrosion rate and the actual corrosion rate in the figure have been calculated based on Equation (8) and Equation (9), respectively. The actual corrosion rate of the concrete specimens remains below the theoretical value throughout the corrosion process. Due to earlier cracking in the NC specimens, the rate of increase in steel reinforcement corrosion remains relatively stable, around 70% of the theoretical value. For the UHPC specimens, the corrosion rate  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample Number** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** \\ \hline Concrete Short Column & 50.0 & 49.3 & 50.0 & 50.0 & 49.8 & 49.6 & 48.4 & 49.4 & 48.0 \\ \hline UHPC Short Column & 50.0 & 48.7 & 48.8 & 48.4 & 48.0 & 49.5 & 46.2 & 49.3 & 43.0 \\ \hline Difference & 0.0 & 0.6 & 1.2 & 1.6 & 1.8 & \(-0.1\) & 2.2 & 0.1 & 5.0 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The remaining length of the reinforcement after corrosion (cm).  
Figure 8: Steel reinforcements’ actual corrosion situation.  
increases very slowly in the early stages; as cracks develop, the rate of corrosion acceleration gradually increases, and, after 30 days, the corrosion rate for the UHPC specimens stabilizes around 40% of the theoretical value. This indicates a significant difference in the corrosion rate trends between the UHPC and concrete specimens. Similar to the conclusions from the above studies, research by [PERSON] et al. [46, 47] found that the actual corrosion rate of ordinary concrete after accelerated rusting is approximately between 60% and 70% of the theoretical corrosion rate. Additionally, [PERSON]'s study showed that concrete with a higher strength exhibited a lower corrosion percentage and was less prone to crack development after accelerated rusting [48].  
The linear fitting of the actual corrosion rates for the concrete and UHPC short column specimens is shown in Figure 11. The fitting results indicate that the concrete specimens, which exhibit earlier cracking, can be represented with a single linear fit. In contrast, the  
Figure 10: The corrosion rate of the short column specimens over time: (**a**) the corrosion rate curve for the NC specimens and (**b**) the corrosion rate curve for the UHPC specimens.  
Figure 9: Changes in the cross-sectional corrosion of reinforcement in concrete and UHPC short columns.  
UHPC specimens require two linear segments for fitting. This is because cracks in the UHPC specimens appear around day 17 (U5). Prior to crack formation, chloride ions have difficulty reaching the steel surface to cause corrosion. However, once corrosion reaches a certain level, the expansion caused by rusting increases crack formation, significantly accelerating the corrosion rate. This observation aligns with the experimental results.  
From the analysis above, it can be observed that, regardless of the type of specimen, the change in the corrosion rate is related to the migration rate of chloride ions into the specimen, which is closely linked to the porosity of the concrete. This relationship is well-validated by the corrosion changes in UHPC specimens before and after crack formation, explaining why UHPC has significantly better corrosion resistance compared to ordinary concrete.