Modern bridge anti-corrosion coating adopts heavy anti-corrosion coating system. The long-lasting anti-rust primers are zinc-rich primers (zinc powder content requirement 80%); high weather resistance topcoats are acrylic polyurethane topcoat, fluorocarbon topcoat, acrylic polysiloxane topcoat; and the inside of the box beam light-colored high-solid epoxy paint is used.
In the above system, if the corrosive environment reaches C5-I/C5-M, the thickness of the high-build epoxy mica iron oxide intermediate paint can be increased to 150-200μm, and the total dry film thickness can exceed 320μm.
Anti-rust treatment on the surface of steel structure: (thermal spray metal aluminium/zinc, epoxy zinc rich primer, inorganic zinc rich primer, glass flake coating)
Intermediate coating: (high solid epoxy mica iron oxide intermediate paint, epoxy glass flake paint)
High-performance topcoat: (acrylic polysiloxane, fluorocarbon resin coating, acrylic polyurethane)
The anti-rust treatment of the substrate surface of the bridge steel structure mainly uses the self-sacrificing effect of zinc and aluminum for cathodic protection, which greatly reduces the corrosion of the steel and makes future maintenance simple. There are three main methods: metal thermal spraying, zinc galvanizing, and applying inorganic zinc silicate primer.
1) Shop primer: also known as maintenance primer, it is mainly used in the primary surface treatment stage of steel and is used for temporary protection of steel in the cutting and welding assembly stage. The most used in the bridge steel structure is the inorganic zinc silicate shop primer. It has excellent mechanical properties, good heat resistance, and less damaged surface during hot working.
2) Zinc-rich primer is an important anti-rust primer in bridge steel structure, it is mainly epoxy zinc-rich primer and inorganic zinc silicate primer. In the steel structure multi-layer coating system, the performance of epoxy zinc-rich primer and inorganic zinc-rich primer are basically the same. From the perspective of construction and construction speed, epoxy zinc-rich primer is more suitable.
In the bridge anti-corrosion system, the high-build epoxy coating is mainly used as intermediate paint of the exposed steel structure and the anti-corrosion coating inside the steel box girder. Epoxy mica intermediate paint is with solid content of 80%, one coating layer can reach a dry film thickness of 150μm or more. Inside the box girder, epoxy zinc phosphate and high build epoxy coatings can be used.
Acrylic polyurethane topcoat has good outdoor weather resistance, excellent gloss and color retention, and no maximum recoating interval. It is currently the most widely used topcoat in the system for steel structure anticorrosion.
Fluorocarbon topcoat has super weather resistance and chemical resistance, and its stability is the best among all resin coatings.
Polysiloxane coating is a high-performance anti-corrosion topcoat without isocyanate. It provides stronger stability and better weather resistance and degradation resistance and is maturely used in heavy anti-corrosion fields such as offshore platforms, ships, bridges, and storage tanks.