It used to be that painting was your only choice to protect steel bridges from corrosion. But now, you have two additional corrosion protection choices: Weathering Steel and Hot Dipped Galvanization.

Weathering Steel is intentionally left unpainted so that a thin outer layer can rust. This outer layer forms a protective barrier that prevents further rusting.

Hot Dipped Galvanization is the process of coating steel elements by fully immersing each piece in a zinc alloy, which forms a protective barrier against corrosion.

While both Weathering Steel and Hot Dipped Galvanization can significantly reduce future maintenance efforts and cost, you should first evaluate whether these options are suitable and feasible for your particular project conditions.

Weathering Steel. In considering the use of Weathering Steel at a site, it is recommended that this option not be used where a bridge has prolong exposure to salt spray, chemical fumes, or wet conditions. The Weathering Steel may not form its protective layer or may delaminate during the corrosion process and lose large amounts of its section. This may occur in areas where vertical clearances are close to travel lanes of the roadway below, or in industrial areas where chemical fumes may drift onto the structure. Wet conditions to be avoided include sites where there is little clearance between a bridge and normal water level (2.5 meters or less), where a bridge is exposed to spray from a waterfall or spillway, in areas of frequent rainfall, high humidity, or persistent fog, or in marine coastal areas.

If you use Weathering Steel, the bridge deck should be constructed from a relatively impermeable material such as concrete. The use of open steel grate decks and timber decks are not recommended for use with Weathering Steel.

Hot Dipped Galvanization. Recent advancements in Hot Dipped Galvanization have made this a feasible alternative not only for bridges built from small steel members, such as truss bridges, but for small to medium span beam bridges. Currently, steel beams for bridges as large as 80-feet in length can be Hot Dipped Galvanized, making this a potential alternative for many short span crossings.

A consideration in deciding whether to use Hot Dipped Galvanization is the availability of facilities that can handle the size of your bridge elements. Because only a limited number of plants can handle larger beam elements, you will need to decide if the particular needs of your project can be accommodated .

Since there are limitations associated with both Weathering Steel and Hot Dipped Galvanization, you may find that painting is your only option. If so, try to incorporate jointless deck construction into your bridge design to minimize paint system failure at these common problem areas.

For more information on using Weathering Steel or Hot Dipped Galvanization on your bridge projects, contact Dennis Judson at (585) 334-1310, ext. 226 or djudson@fisherassoc.com.