## 3 Result and Discussion
### Failure Process and Form of Columns  
Figure 9 shows physical diagrams of the uncorroded and stirrup-corroded axial compression columns when they reached the failure stage. During the loading process, it was found that the failure process and failure form of the uncorroded and corroded columns were not exactly the same. At the beginning of loading, the load displacement of the uncorroded column with stirrups increased in a certain proportion, and there was no obvious change in the external surface of the compressed column. When the ultimate load was nearly reached, the vertical loading cracks extended from the end of the column to the middle. After exceeding the ultimate load, the cracks on the surface of the column developed rapidly, part of the concrete cover of the concrete flaked off, and the core concrete was crushed while the whole test column was damaged. During the damage stage, the stirrups were deformed in tension and the longitudinal bars between the stirrups were locally flexed, with the flexion length being the length of the stirrup spacing without crossing more stirrups, indicating that the stirrups played an effective restraining role on the longitudinal bars and the strength of the longitudinal bars was fully utilized.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen Number** & \(\rho_{\text{ve,ce}}/\%\) & \(l_{c}/\text{mm}\) & \(W_{\text{max}}/\text{mm}\) & \(W_{\text{ave}}/\text{mm}\) \\ \hline GZ0 & 0.00 & 0 & 0.000 & 0.000 \\ GZ5 & 4.95 & 1050 & 0.649 & 0.228 \\ GZ10 & 9.26 & 2350 & 0.730 & 0.234 \\ GZ15 & 12.57 & 3150 & 0.851 & 0.258 \\ \hline \hline \end{tabular} Note: \(l_{c}\) is the total length of the corrosion-induced cracks; \(W_{\text{max}}\) and \(W_{\text{ave}}\) are the maximum and average width of the corrosion-induced cracks, respectively.  
\end{table}
Table 3: Total length, maximum, and average width of corrosion-induced cracks.  
Figure 9: The destruction patterns of concrete columns. (**a**) GZ0; (**b**) GZ5; (**c**) GZ10; (**d**) GZ15.  
For the stirrup-corroded columns, the width of the original corrosion-induced cracks on the surface of each corrosion column increased with the load. When the ultimate load was nearly reached, new vertical loading cracks appeared at the end of each corroded column one after another and penetrated with some of the corrosion-induced cracks. When the ultimate bearing capacity of each corroded column was reached, the width of the corrosion-induced cracks and the loading cracks on the surface of the column developed rapidly, and the concrete cover spalled off in pieces along the corrosion-induced cracks and the newly developed loading cracks. The higher the stirrup corrosion rate, the more serious the spalling of the concrete cover. Eventually, the concrete in the core area was crushed, resulting in obvious brittle damage to the test column. When the column reached the failure stage, the stirrups were severely deformed in tension and the longitudinal bars were deformed in flexure across several stirrups, which did not form an effective restraint on the longitudinal bars and the strength of the longitudinal bars could not be fully utilized. After the concrete cover of each corroded column was peeled off, red corrosion products (Fe\({}_{2}\)O\({}_{3}\)) and some black corrosion products (Fe\({}_{3}\)O\({}_{4}\)) were clearly observed attached between the core concrete and concrete cover. These corrosion products caused delamination of the concrete cover and core concrete. Under the action of axial pressure, due to the Poisson effect, the concrete cover withdrew from the work in advance. The effective bearing of the cross-sectional area of the test column was reduced, which decreased the load bearing capacity. In conclusion, the influence of stirrup corrosion on concrete section damage, longitudinal reinforcement buckling, and reduction of core concrete restraint should be considered when analyzing the bearing capacity of corroded reinforced concrete columns.