In the repair of prestressed steel corrosion, understanding the hydrogen effect is vital, as it significantly influences the safety and effectiveness of various repair methods. The commonly employed techniques for addressing this issue are impacted by the hydrogen phenomenon when applied to prestressed steel repairs. The durability repair techniques for concrete structures primarily consist of electrochemical and physical repair methods. Physical repair methods aim to treat mild corrosion on steel bars by rust removal and preventative measures. In cases of extensive rust, deteriorated concrete layers are removed, and the steel bars may be reinforced or replaced. On the other hand, electrochemical repair techniques encompass various technologies, including sacrificial anode cathodic protection, impressed current-assisted anode methods, electrochemical dechlorination, electrochemical re-alkalization, electromigration rust inhibitor technology, and bidirectional electromigration technology. While these technologies are available for repairing steel corrosion, their application scope and engineering effectiveness still require enhancement. The repair processes for PC WIRE corrosion largely depend on traditional methods for ordinary steel corrosion, yet some lack practicality for prestressed steel repairs. Below are the prevalent repair methods.
This method involves connecting a metal with a more negative potential to the steel bars within the concrete. During the reaction, the anode material, typically zinc, helps protect the steel bars by self-consumption and dissolution. Given that zinc has a lower potential than steel, the anodic reaction occurs first. However, when the potential difference is significant, the hydrogen evolution reaction may occur on the surface. Additionally, if the current applied using the auxiliary anode method of impressed current is excessive, hydrogen evolution reactions may also take place at the cathode. A critical concern for prestressed steel bars is the risk of hydrogen embrittlement failure, which leads to brittle fractures. Consequently, it is generally not advisable to employ sacrificial anode methods or impressed current auxiliary anode methods for prestressed steel corrosion repairs without addressing the material's sensitivity to hydrogen embrittlement, the current flow in the prestressed steel, and the repair efficiency affected by current levels.
This method serves as an effective approach to eliminate chloride ions from reinforced concrete. In this process, the steel bar acts as the cathode, while an external metal sheet serves as the anode. Voltage is applied to restore the passivation of the PC steel bar by removing chloride ions. The dechlorination system closely resembles a cathodic protection system that utilizes an external power supply. A significant difference lies in the frequent use of temporary anodes and a higher current density compared to cathodic protection. While this method is simple and cost-effective, it poses challenges for prestressed steel repairs, such as the generation of hydroxide ions on the steel bar's surface and increased alkalinity that may lead to alkali aggregate reactions.
In this method, a direct current is applied between the external electrode placed on the concrete component and the steel bar, with the external electrode functioning as the anode and the steel bar acting as the cathode. This process leads to cathodic polarization of the steel bar and results in the generation of hydroxide ions, which enhance the alkalinity surrounding the concrete. This alkalinity is essential for maintaining the passive film on the steel surface and ensures the successful re-alkalization of the steel.
Applying a small current to the concrete creates an electric field that facilitates the migration of cations to the surface of the concrete, where precipitates form and effectively block microcracks. This technique is particularly useful for repairing concrete microcracks in submerged environments and is notably effective against corrosion caused by chloride salts. The key to successful application lies in selecting the right electrodeposition solution.
This method employs a stainless steel mesh placed on the concrete's outer surface, with the steel bar serving as the cathode and the metal mesh acting as the anode. When an electric field is applied, cations electrolyzed by the rust inhibitor migrate to the steel bar's surface, concurrently eliminating chloride ions and thereby protecting the steel bar.
In conclusion, the aforementioned methods represent five widely utilized technologies for addressing steel bar corrosion. Ongoing research and development are necessary to enhance these methods for more efficient repairs and greater applicability to prestressed steel scenarios.
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