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Hot-dip galvanizing of steel bars will become one of the important emerging markets for hot-dip galvanizing in the future

Category: Industry News Publish Time：2018-09-27

Can steel bars for reinforced concrete be hot-dip galvanized? Reinforced concrete structures often suffer from steel bar rust and concrete spalling due to external factors such as vehicle impacts, insufficient cover, concrete carbonation, the misuse of sea sand, and environmental factors, leading to steel bar rust or water ingress through cracks in the concrete causing steel bar rust. Methods to prevent steel bar rust include improving concrete quality and protecting the steel bars to protect the concrete structure. Of course, if the concrete composition can be controlled, such as the penetration of water, chloride ions, oxygen, and carbon dioxide, even to the surface of the steel bars, or the construction of reinforced concrete structures is truly implemented

　　Is it possible to hot-dip galvanize steel bars used in reinforced concrete?

　　Reinforced concrete often suffers from steel rust and concrete spalling due to external factors; for example, vehicle impacts, insufficient protective layers, concrete carbonation, misuse of sea sand, and environmental factors, etc., causing steel rust or water ingress into concrete cracks, leading to steel rust.

　　Methods to prevent steel rust can be divided into enhancing concrete quality and protecting steel bars to protect concrete structures. Of course, if the composition of concrete can be controlled, such as the penetration of water, chloride ions, oxygen, carbon dioxide, etc., or the construction quality of reinforced concrete structures is truly implemented, then the steel bars may not need any further protection to achieve the required quality.

　　However, these influencing factors are often visible during construction, so steel bars should be protected as much as possible.

　　Steel bar protection generally includes hot-dip galvanizing and epoxy resin coating.

　　These two methods have their own advantages and disadvantages. A large number of experimental results show that hot-dip galvanized steel bars have better handling and processing performance on site, and can exert their superior characteristics in engineering, improving the reliability and corrosion resistance of the project, and making the project more economical.

　　Content of the reaction between the zinc layer of hot-dip galvanized steel bars and concrete

　　Alternatives to concrete protective layer thickness still need to be used correctly and appropriately, and the reaction between zinc and concrete includes:

　　(1) The reaction between zinc and Ca(OH) 2的反应。

　　(2) Purification of the zinc surface.

　　(3) Hydrogen generation.

　　Because concrete has a high alkaline environment (PH=12.5～13.2), a pure protective layer is formed on the surface of the steel bars, which is an effective barrier to protect against steel corrosion, just as it protects the steel bars. Zinc is an amphoteric element (it can react with acids and alkalis), and its lowest corrosion rate is at PH=12.5, which is equivalent to the PH value of cement hydration.

　　Zinc will dissolve at PH=8～12.5, and after the concrete hardens, the reaction between zinc and the alkaline environment will stop.

　　The net reaction of zinc and calcium hydroxide forms a zinc-passivated zinc hydroxide calcium barrier layer, but it is also accompanied by the generation of hydrogen, which may cause damage to the "bond" between the concrete and the steel bars and produce pores. In this case, a small amount of chromate (70～100ppm) can be added to the cement to overcome the generation of hydrogen, only preventing construction personnel from being harmed by chromic acid or chromates during work.

Keywords: Hot-dip galvanizing of steel bars will become one of the important emerging markets for hot-dip galvanizing in the future

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