National Steel Bridge Alliance


Corrosion Protection and Durability Resources

There are several proven ways to protect steel bridges from corrosion, and no single solution is best for all circumstances.

The first consideration when selecting one of these techniques is, of course, a bridge’s anticipated exposure to corrosive elements over its lifetime. In addition, teams must consider initial and life-cycle costs, fabrication, productivity, and long-term performance and maintenance when choosing a corrosion protection approach for a given bridge.

General resources:


 

Some corrosion protection options:

 

Uncoated weathering steel (UCWS) is designed to form a stable patina that protects the structural integrity of the member. Uncoated weathering steel is a widely used corrosion protection system today and performs well if detailed properly and used in the proper location and environment.

For additional information, please refer to:

A note about tunnel-like conditions:



One-coat inorganic zinc (IOZ)
is a relatively thin silicate coating that has performed well in marine atmospheric conditions. 

  • The Washington State DOT constructed two bridges in the early 2000s with only IOZ primer; an organic zinc primer was also applied to bolted connections in the field. The IOZ primer on both bridges are performing well and the bolts/connections are also in good condition.  

    • The U.S. 2 Barclay crossing bridge was constructed in 2003 approximately 40 miles east of Bellevue, Wash.  

    • The U.S. 101 Nolan crossing bridge was constructed in 2004 approximately 5 miles east of Oil City, Wash. and the Pacific Ocean.  

         



Two-coat paint systems
consist of a zinc-rich primer followed by a polyaspartic, polysiloxane, or acrylic finish coat.  



Three-coat paint systems
are a common coating system used to protect steel bridges  Traditionally, these systems consist of a zinc-rich primer followed by an epoxy mid-coat and a polyurethane top coat. Sometimes these systems also use a clear coat on fascia girders for enhanced resistance to ultraviolet light in southern latitudes.



Metallizing/thermal spray coatings (TSC)
involve a metal coating that is applied to a substrate, like steel. The most common coating choices for bridge steel are pure zinc, pure aluminum, or an alloy of 85% zinc and 15% aluminum.



In
hot-dipped galvanizing (HDG), steel elements are dipped into molten zinc to create a protective layer.



Stainless structural steel (A709-50CR)
generally contains more than 10.5% chromium and is a relatively new steel alloy. The industry continues to develop new alloys that are more cost-effective. 

Section 3.4 (p 21) of Volume 19 of the FHWA Steel Bridge Design Handbook summarizes additional corrosion-resistant alloys, such as A709-50CR.