In practical engineering, there are three main protection methods for steel corrosion.
1. Protective film method
The protective film is used to isolate the steel from the surrounding medium, to avoid or slow down the destructive effect of the external corrosive medium on the steel. For example, spray paint, enamel, plastic, etc. on the surface of steel; or use metal coating as a protective film, such as zinc, tin, chromium, etc.
2. Electrochemical protection method
The specific cause of the corrosion can be divided into the no-current protection method and the impressed current protection method.
The no-current protection method is also called the sacrificial anode method. It is to connect a metal that is more active than steel, such as zinc and magnesium, to the steel structure. Because zinc and magnesium have a lower potential than steel, zinc, and magnesium becomes the anode of the corrosion battery. damaged (sacrificial anode), while the steel structure is protected. This method is often used for places where it is not easy or impossible to cover the protective layer, such as steam boilers, underground pipelines of ship shells, port engineering structures, road and bridge buildings, etc.
The applied current protection method is to place some scrap steel or other refractory metals near the steel structure, such as high-silicon iron and lead-silver, and connect the negative pole of the external DC power supply to the protected steel structure, and the positive pole is connected to the refractory metal structure. On the metal, after electrification, the refractory metal becomes the anode and is corroded, and the steel structure becomes the cathode and is protected.
3. Taijin Chemical
Carbon steel is added with elements that can improve corrosion resistance, such as nickel, chromium, titanium, copper, etc., to make different steels.
The above methods can be used to prevent the corrosion of steel bars in reinforced concrete, but the most economical and effective method is to improve the density and alkalinity of concrete and to ensure that the steel bars have sufficient protective layer thickness.
In the cement hydration product, due to the calcium hydroxide of about 1/5, the pH value of the medium is about 13, and the presence of calcium hydroxide causes a passivation film on the surface of the steel bar to form a protective layer. At the same time, calcium hydroxide can also act with atmospheric clock CQ to reduce the alkalinity of concrete, the passivation film may be destroyed, and the steel surface is in an activated state. In a humid environment, electrochemical corrosion begins to occur on the surface of the steel bar, resulting in the cracking of the concrete along the bar. Therefore, the carbonization resistance of concrete should be improved by improving the compactness of concrete.
In addition, chloride ions have the effect of destroying the passivation film. Therefore, when preparing reinforced concrete, the amount of chloride salt should be limited.
Post time: Oct-10-2022