Corrosion Behavior of Coupled Steel Bars under Different Stress Levels in Simulated Concrete Pore Solutions

To study the corrosion behavior of coupled steel bars under applied stresses, experiments on the influence of applied tensile and compressive stresses on the corrosion of coupled steel bars in simulated concrete pore solutions were conducted. The corrosion processes of the individual steel bars and coupled steel bars with different stress levels, including three tensile stress levels ($1/3f_{\mathrm{y}}$, $2/3f_{\mathrm{y}}$, and $3/3f_{\mathrm{y}}$) and three compressive stress levels ($-1/3f_{\mathrm{y}}$, $-2/3f_{\mathrm{y}}$, and $-3/3f_{\mathrm{y}}$), were monitored regularly, by several electrochemical measurements, in chloride contained simulated concrete pore solution for 45 days. The experimental results showed that applied stresses had significant effects on the corrosion of steel bars. In a chloride-free environment, the applied tensile stress was found to protect the passive film. However, once corrosion initiated, the applied tensile stress would aggravate the corrosion, while the applied compressive stress might inhibit the corrosion. Microcell corrosion and macrocell corrosion were significantly influenced by the applied stresses. The applied stresses might alter the corrosion mode. Tensile-stressed steel bars and compressive-stressed steel bars showed the susceptibility to the pitting corrosion. By comparison, steel bars with applied tensile stresses tended to corrode more uniformly; however, those with applied compressive stresses were more likely to undergo localized corrosion.

Reinforced concrete structures usually endure various loads such as traffic and wind loads. The external loads have been proven to influence the corrosion process of steels in concrete. However, the specific principles and results of the effect of external loads on the corrosion of steels have yet to be thoroughly studied. This study aims to investigate the corrosion process of steel under different stress levels in a simulated concrete environment. Compared with an experiment in practical concrete structures, an experiment in simulated concrete pore solutions has a shorter test cycle and the experimental phenomena are more obvious. The results show that the applied tensile stress will aggravate the corrosion of steel, while the applied compressive stress will restrain the corrosion process. Based on the research results, engineers should pay attention to the effect of external loads on the durability of structures in the design stage. Moreover, this study provides a reference for further experimental studies in practical reinforced concrete structures.