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Macrocell corrosion of steel rebar in concrete induced by corrosive environments has attracted widespread attention in the engineering community due to its rapid corrosion rate, diverse forms, and multiple incentives. Potential differences between dissimilar coupled rebar or different parts of the same rebar mainly cause macrocell corrosion of steel rebar. The more significant the potential difference, the faster the corrosion rate of the macrocell. Based on the existing research reports on macrocell corrosion of reinforced concrete, this review paper comprehensively discusses the macro- and micro-corrosion behavior of various types of steel rebar, and a variety of induction factors, such as dissimilar metals and concentration differences of the service environment, development rules. and electrochemical mechanisms for corrosion of rebar macrocells are summarized. ZRA (zero-resistance ammeter), micro-area electrochemical testing technology and evaluation techniques commonly used in the laboratory, and electrochemical testing techniques used in engineering testing are listed. Common experimental models for corrosion of rebar macrocells are briefly introduced. Based on the internal characteristics of macrocell corrosion of reinforced concrete, this paper further proposes the control strategy of macrocell corrosion, starting from the improvement of the corrosion resistance of the rebar and regulating the service environment of the reinforced concrete structure (RCS). Meanwhile, the future direction of macrocell corrosion of steel rebar is also preliminarily prospected.

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Surface nanocrystallization (SNC) modification can be used to realize the high-efficiency derusting of rusted Cr-alloyed rebar and obtain nanostructured grains on the surface of the rebar. The corrosion resistance performance of SNC rebar in a simulated Cl--containing concrete pore solution was evaluated on the basis of electrochemical experiments. Potentiodynamic polarization testing showed that the passivation current density of the SNC rebar was about 18% of that of the rusted rebar. The structural composition of the passivation film of the SNC rebar in a concrete environment was studied using a novel characterization method, namely XPS deep sputtering, which confirmed that it had higher concentrations of Cr/Fe oxide and hydroxide, and therefore exhibited an enhanced degree of oxidation. Moreover, scanning electron microscopy and transmission electron microscopy were employed to investigate the microstructural characteristics of the SNC rebar, which was characterized by nanostructured grains with grain sizes ranging from 250 nm to 300 nm and which contained massive high-energy crystal defects, thereby promoting the film-forming reaction of Cr/Fe elements. The results of XPS depth analysis and microstructure characterization demonstrated that the SNC rebar exhibited excellent passivation performance in the concrete environment. These findings offer a new perspective on enhancing the passivation performance and chloride resistance of alloyed rebar, and provide guidance on the implementation of SNC rebar in actual engineering applications.