The Effects Of Non-uniform Corrosion On Mechanical Degradation Of Corroded Steel Bars In Concrete Structures

Steel corrosion in reinforced concrete structures results in degradation of its mechanical performance and bond deterioration between corroded bars and concrete, which greatly impair the structural safety and shorten service life of the corrode structures.In this research work, corroded reinforcing bar specimens were prepared using galvanostatic method, and solid models of the bar specimens were built using an advanced 3D laser scanning technique. Geometry parameters of the corroded bar were precisely measured on the models by Pro/E software, and a practical factor was proposed to quantitate the non-uniform corrosion distribution. Finally, the corroded bars were tested in tension to obtain the real load-deformation curves under 100 mm and 50 mm gauges. Based on the experimental results, the distribution model of residual cross-sectional area were carefully observed along the length of the tested bar sections, and a simplified linear distribution model of discrete cross-sectional areas was proposed reasonably. Numerical tensile test, through integration of load-deformation behaviors of subsections, was realized on the hypothesis of constant residual area inside an individual subsection and real mechanical properties remaining unchanged. This numerical test model was verified by experimental results before it was used to carry out detailed research on influence of non-uniform corrosion upon the mechanical properties of corroded bars including elastic modulus, yield strength, ultimate strength, ultimate strain, etc. The aim of the work was to explore the effect of non-uniform corrosion on nominal mechanical indices of corroded bars, to understand the degradation mechanisms induced by corrosion; and to set up degradation models of the nominal indices.Shown by the results, no evidence leads to the conclusion that real mechanical performance of steel bars would degrade as the corrosion develops, and the degradation concluded in the previous research work can be explained by the effects of non-uniform corrosion on the nominal parameters. Nominal elastic modulus suffer a slight decrease due to the non-uniform corrosion, however, it can be ignored considering the decrease would be less than 1% under the most severe circumstance. Non-uniform corrosion results in gradational yielding of the residual cross-sections, which consequently leads to gradual inclination of the yield plateau in load-deformation curve until it entirely merges into the strain hardening branch. Under severe pit corrosion, prior yield strength of corroded bars may be reduced by the stress concentration, while posterior yield point remains unchanged suggesting the ideal elastic-plastic property of corroded steel. Ultimate strength of corroded bars is mainly determined by the minimum residual cross-sectional area, thus the nominal ultimate strain will also drop greatly as the non-uniform corrosion distribution increases. Based on the understanding of influence mechanisms of non-uniform corrosion and correlation being built between corrosion non-uniform distribution coefficient and corrosion degree, computing models of the nominal parameters of corroded bar properties are finally built on average corrosion ratio, which are highly practical in field applications.