| Against severe corrosion of reinforced rebars in marine environment, the utilization of corrosion resistant rebars is the last bulwark of protection. However, high prices of stainless rebars raise the construction cost. Therefore, in this paper, three kinds of corrosion resistant low alloy rebars were obtained through adding Cr to HRB400 carbon steel. Electrochemical measurements combined with XPS, AES, and XRD were employed to investigate chemical composition of passive film and corrosion products, and indoor accelerated tests were carried out in comparison of marine field tests. The conclusions are listed as below:（1） In saturated Ca（OH）2 solution, as immersion time elapses, open circuit potential of low alloy steel rebars shifts positively and gets stability at about-250mV （SCE）. With Cr content increasing, polarization resistance magnifies. It takes at least 72h to form a stable passive film. In general, corrosion resistance of low alloy steel rebars is higher than that of HRB400 carbon steel.（2） In simulated concrete pore solution, passive film of the corrosion resistant low alloy steel rebars are mainly composed of iron oxides. In 3Cr and 5Cr steel rebar, CrO3 and Cr（OH）3 appears. The thickness of passive film is 5-6～6nm approximately, and increases slightly as Cr content goes up. Fe oxides are dominant in the outside layer of passive film, while Cr participates in the formation of the iner layer.（3） Corrosion resistant low alloy steel rebars possess excellent corrosion resistance against carbonation of concrete. As pH declines, stability of passive film decreases. The involvement of Cl" brings down pitting potential of steel rebars and results in the increases of defects and decreases of corrosion resistance of passive film. The increases of Cl- plays a more significant role in the decreases of corrosion resistance at lower pH values. At an individual test condition, corrosion resistance of rebars in sequence from high to low is: 5Cr>3Cr>1.5Cr>HRB400.（4） Cr modified low alloy steel rebars exert higher critical chloride concentration. At 25℃, the critical chloride concentration of 5Cr steel is the highest ant 6.2 times of that of HRB400 carbon steel. The rise in temperature decreases the critical chloride concentration of rebars in simulated concrete pore solution. The utilization of corrosion resistant rebars is capable of postponing corrosion initiation time to some degree,5Cr steel has the longest durability.（5） Corrosion resistant rebars present low radial corrosion resistance and high circular corrosion resistance. Pitting factor increases as Cr content is elevated. The utilization of corrosion resistant rebars can prolong the corrosion crack of rebar in concrete.（6） Indoor alternating wet-dry experiments show that polarization resistance increases and corrosion current density decreases with Cr content rising.5Cr steel possesses the highest corrosion resistance. Fe oxides are predominant in corrosion products of rebars, in particular, α-FeOOH in 1.5Cr and 5Cr steel. In Cr containing rebars, Cr enrichment happens in the rust layer close to the metal base and thus lowers corrosion.（7） One-year marine field tests in Zhanjiang seawater corrosion station reveal that the surface of ordinary and high-performance epoxy coating is intact without obvious corroded area. Among bare rebars, localized corrosion appears on HRB400 steel and 1.5Cr steel while there is no apparent rust on the surface of 5Cr steel, which proves 5Cr steel higher critical chloride concentration and more corrosion resistance. Corrosion products of HRB400 steel and 1.5Cr steel are mainly made up of Fe oxides, which coincides well with results of indoor accelerated tests. |
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