Hot-dip galvanizing is the core surface treatment process for hot-dip galvanized bridges. However, other auxiliary treatments may be combined or derived during production to further enhance performance or meet specific requirements. These include:
Passivation: After hot-dip galvanizing, a passivation treatment using a chromate solution or other methods forms a passive film on the zinc surface. This enhances the zinc's corrosion resistance and prevents the formation of "white rust" (a corrosion product of zinc) during storage or use.
Phosphating: In some cases, the steel surface is phosphated before galvanizing to form a phosphate film. This improves the bond between the zinc layer and the base steel and enhances the adhesion of subsequent coatings (such as paint) if additional coatings are required.
Painting or plastic spraying (composite treatment): In particularly corrosive environments, a layer of paint or powder coating (such as epoxy resin) may be applied over the hot-dip galvanized layer to create a "zinc + coating" composite protective system, further enhancing corrosion resistance and improving the appearance.
These processes are mostly auxiliary or enhancement means of hot-dip galvanizing, and the core is still based on hot-dip galvanizing, which improves the durability of the bridge through multi-layer protection.
