Page 259 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION CONTROL OF BRIDGES 237

used it on an experimental basis, a spray-on delivery of a liquid reagent for anti-icing
of certain sections of the Brooklyn Bridge deck.

4.9.2 Steel Bridges
A discussion of various steel bridge coating installation and maintenance options
along with the costs and expected life is as follows. In addition to the traditional coat-
ing methodologies used on steel bridges, research has identified several technologies
and maintenance methods such as:

1. Zone painting.
2. The use of overcoating or maintenance repair painting techniques.
3. The selected use of metal spray coatings.

4.9.2.1 Traditional Coating System A two to three coating system is traditionally
applied over a clean, blasted system. These coating systems are the following (33):

1. Organic zinc primer, epoxy or polyurethane intermediate coat, and aliphatic
polyurethane top coat.
2. Inorganic zinc silicate polymer, chemically curing epoxy or polyurethane inter-
mediate coat, and aliphatic polyurethane top coat.
3. High-build high solids, good-wetting epoxy primer with aliphatic polyurethane
topcoat
4. Three-coat waterborne acrylic
5. Three-coat, lead-free alkyd.

4.9.2.2 Zone Painting Because of the high cost of repainting the whole bridge
structure, it has become economically attractive to use zone painting. This approach
is particularly attractive for larger structures and has been used on structures such
as the Golden Gate and the Bay Bridges in California and others in the New York
City area. These larger bridges have different exposure environments within the same
structure because of their size and their location near saltwater. These bridges are toll
bridges and have greater resources to focus on intermittent or periodic maintenance
activities.
The vast majority of bridges in the United States are neither large nor maintained
by toll authorities. The cost of full removal and repainting of even smaller structures
is relatively high. Even on smaller structures, coating breakdown and corrosion is
limited to areas with measurable levels of salt contamination and significant amounts
of wetness.
For bridges in marine or semimarine environments, the entire structure is subject
to corrosion. In the case of bridges in nonmarine environments, the corrosive areas are
generally limited to expansion joints, drainage, traffic splash, and tidal areas. If these
areas can be isolated and maintained by a better protection system, large expenses
can be avoided in the maintenance of the bridges. Improved inspection procedures
and standards will also be a positive contribution.