| Steel corrosion is one of the most important factors to influence the durability of concrete. In fact, the corrosion problem has been the main reason for the early failures of major projects and the whole world has paid much attention to this problem. There are several measures to avoid this problem, including stainless steel, protective coat and fiber reinforced polymer (FRP) rebar. However, high cost and poor mechanical property are the disadvantages of these measures, which constrains the application of these measures. On the contrast, alloyed corrosion-resistant steel rebar performs well in aspects of both cost and mechanical property. As the fundamental measure to guarantee the durability of concrete structure, the research on the durability of corrosion-resistant steel rebar has great value for the optimization and application of corrosion-resistant steel rebar.Corrosion resistance and corrosion sensitivity to chloride containing environment of corrosion-resistant steel rebar (CR), low carbon steel rebar (LC) and stainless steel rebar (SS) were comparatively investigated by electrochemical behavior. The integrated formation and chloride-induced process of passive film of CR rebar was characterized by XPS, TEM, AFM and M-S curve and corresponding information of chemical composition, structure and morphology of passive film of CR rebar. Combined with diffusion dynamics, surface science and thin film formation theory, the passivity and chloride-induced corrosion mechanism has been revealed.The main conclusions of this paper are listed as follow:The change range of the impedance capacity reactance arc and passive film resistance of corrosion-resistant steel rebar during first 3-hour immersion is greater than low carbon steel rebar and stainless steel. The passive films of all the three kinds of rebar react dramatically during first day and slow down afterwards.The integrated impedance, resistance and homogeneity of passive film of CR rebar are all better than LC rebar, and similar to SS rebar. The chloride critical value of CR rebar is approximately 50 times that of LC rebar and equal to SS rebar in the simulated concrete pore solution.The passive film of CR rebar behaves as n-type semi-conductor after 1 hour immersion and switches to p-n type semi-conductor after 3-hour immersion; On the contrast, the passive film of SS rebar performs as p-n semi-conductor the minute immersing in solution; LC rebar performs as n-type semi-conductor. Smaller passive film particles are precipitated on the surface of CR rebar after 1 hour immersion. This may result from the granular bainite of CR rebar substrate which provides more nucleation sites. The Cr content ofpassive film of stainless steel rebar is higher than corrosion-resistant steel rebar after 1 day immersion.The thickness of passive film of CR and SS rebar are both 5nm after 10-day immersion according to XPS and TEM results. The stable passive film structure of CR rebar consists of outer layer (FeOm(OH)n and CrOp(OH)q,0< m; p< 1 and 1< n; q< 3) and inner layer(Fe-Cr) anhydrous oxide. The proportion of Cr-oxide of CR rebar increases after 10-day immersion while that of SS rebar is still the same. This can be explained by the impediment of relatively compact Cr-oxide of SS rebar generated in the first 1 day immersion.The structure and composition distribution of CR and SS rebar are both homogeneous while that of LC rebar is relatively inhomogeneous. The crystallinity of CR rebar is higher than LC rebar and lower than SS rebar.The thickness of passive film of CR rebar decreases even disappears in 5 M chloride. However, the majority of passive film of CR rebar still remains stable. The influence of chloride on the passive film is related to immersion time. In general, the conductibility of CR and SS rebar go up slightly in chloride. |
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