A. Specify method of protection and locations on structure: uncoated weathering steel; Inorganic Topcoat System, or High Performance Topcoat System. Other systems must be approved by the SDO or the DSDO. The final exterior finish color of a High Performance Topcoat system is an aesthetic treatment and must be approved by the DSDO.
B. Specify a white or light grey for box interior colors. Specify Inorganic Topcoat system or the epoxy portion of the High Performance system as the topcoat.
A. Site specific criteria that may require specialty corrosion protection systems:
1.) Locations where the pH of the rainfall of condensation is less than 4 and greater than 10.
2.) Locations subject to salt spray and salt laden run-off.
3.) Locations subject to concentrated pollution caused by the following sources: coal burning power plant, phosphate plant, acid manufacturing plant, any site yielding high levels of sulfur compounds.
B. For sites with any of the above conditions, a review and recommendation from a Coating Professional is required to identify the appropriate corrosion control coating system.
A. The standard system shall be an Inorganic topcoat systems consisting of a zinc based primer and an inorganic topcoat. The color of this system is a uniform grey color similar to Federal Color Standard Number 37866.
B. For aesthetic color, the fascia of the exterior girders may be coated with a High Performance Topcoat system.
A. Specify a high performance topcoat system where an aesthetic treatment requiring color and gloss are needed.
A. Design and specify weathering steel per the FHWA Technical Advisory T5140.22.
B. Sites classified as Slightly Aggressive for Superstructures (See Figure 1-1.) are suitable for the use of weathering steel without long-term, on-site panel testing.
C. Specify ASTM A325 Type 3 bolts for weathering steel.
D. Painting of the exterior girder/fascia may be required for aesthetic appearance.
A. Galvanizing of Bolts for Bridges: Normally, all anchor bolts, tie-down hardware, and miscellaneous steel (ladders, platforms, grating, etc.) are to be hot-dip galvanized. While ASTM A307 (coarse thread) bolts must be hot-dip galvanized, A325 (fine thread) bolts must be mechanically galvanized when utilized with galvanized steel components. Other applications not requiring full tensioning of the bolts may use hot-dip galvanized A325 bolts.
B. Galvanizing of Bolts for Miscellaneous Structures: Specify hot-dipped galvanized bolts for connecting structural steel members of miscellaneous structures such as overhead sign structures, traffic mast arms, ground-mounted signs, etc.