The long-term exposure testing was conducted for 5 years in three marine locations. Panels were exposed on two bridges, one in New Jersey and one in southern Louisiana. The third long-term exposure location was in Sea Isle City, New Jersey. Thirteen coating systems were included for long-term exposure testing. These included 2 high-VOC controls and 11 test systems having a VOC level of 340 g/L (2.8 lbs./gal) or less. Five of the test systems contained high-solids primers, two of the test systems contained waterborne primers, one systems was based on a powder coating, and three systems were metallized.

These metalized coatings were applied by the wire flame-spray process. Coating thicknesses: Zinc .007"-.009", Zinc-15 Aluminum .005"-.007", Aluminum .006"-.0075"

The best performing systems were the three metallized coatings. These were initially less aesthetic than coating systems with high-gloss topcoats, but they displayed near-perfect corrosion performance after 5 to 6.5-year exposure periods. Of the traditional liquid applied coating systems, those incorporating inorganic zinc primers performed the best over near-white blasted and power-tool cleaned surfaces. High-solids epoxy coatings had a tendency to undercut at intentional scribes and rust worse than coatings with zinc-rich primers over less than ideal surface preparations.

Metallized systems consistently provided the best corrosion protection performance. All metallized coatings tested showed no corrosion failure in the aggressive, salt-rich environments over the 5 to 6.5-year exposure periods. Steel panels metallized with aluminum and not sealed with a VOC-compliant vinyl topcoat began to show minor blushing after 4 years of exposure in the most aggressive environment. The metallized panels that were topcoated showed no discoloration over the test period.

Selectively coating the bridge components located in the high-corrosion areas of the structure (i.e., zone painting) with higher performing, more durable corrosion protection materials (e.g. metallizing) can have significant life-cycle cost benefits. While at first the cost of metallizing, particularly on field structures, is more expensive than the application of liquid coatings, the superior durability of metallizing will extend the recoating interval for the structure and reduce overall maintenance cost.

Life-cycle cost analysis comparing field performance of metal spray coatings and liquid coatings makes the use of the former economically attractive in aggressive corrosion environments. As metallizing becomes more widely used on bridges, application equipment and techniques will continue to be improved. These improvements should lower the application costs to be more competitive with the application costs of high-performance liquid coating systems. Metallizing readily accepts liquid topcoats for cosmetic and color uniformity requirements.

The metallized systems provided the best corrosion protection performance of all coating systems tested. The metallized coatings displayed superior resistance to panel rusting, resistance to blistering of the coating, and resistance to undercutting at the intentional scribes. The graphs of the exposure data presented later in this section show the excellent overall performance of the metallized coatings.

The use of a vinyl seal coat on the metallized coatings provided primarily an aesthetic benefit. The performance of the metallized coatings without the seal coats was very similar to the performance of the metallized coatings with vinyl seal coats. This fact indicated that the otherwise dull and (in the case of zinc metallizing) blotchy color of unsealed metallizing can be aesthetically improved by applying a decorative topcoat. Slight rust blushing of some unsealed metallized panels was not seen on any sealed metallized panels.

Expose State agencies to the concepts of Appendix I, Economic Guidelines for Painting Practices. These guidelines explain the benefits of life-cycle cost modeling techniques applied to the bridge painting industry. They also indicate the potential benefits of alternative bridge coating practices, such as the use of metallized coatings and zone painting.

The estimated surface area of all members to be metallized was 5,110 square meters. Using the prime contractors bid price of $505,000, the unit cost of metallizing on this project was $98.83 per square meter.

One of the problems with multiple tiers of contracting (i.e., prime contractor, bridge subcontractor, steel fabricator, and metallizer) is that each level of contractor tends to escalate price quotes to cover costs of overhead and to make some profits. As an example, on this project the metallizer submitted a bid to the fabricator, which computed to be $51.24 per square meter. The fabricator increased this unit cost to $60.28 per square meter for his extra cost incurred in surface preparation and additional handling. We were unable to determine how much the bridge subcontractor increased this bid item, but the final bid price by the prime contractor was almost double the metallizer’s quote. Looking at the metallizer’s bid price, it seems that metallizing can be cost competitive with conventional paint systems.

To further compare metallizing versus painting, the steel fabricator indicated that they would typically quote about $27.45 per square meter for a similar bridge with three shop coats of a standard paint system. Comparing this to the fabricator’s quote for metallizing ($60.28 per square meter), it is obvious that painting is much more economical from a first-cost analysis. The disparity becomes much more pronounced when comparing the prime contractor’s bid price for metallizing to a typical shop painting application ($98.83/square meter vs. $27.45/square meter).

Illinois’ first metallizing project was considered to be successful. Although there were some production problems, the new equipment used showed that metallizing can be done much faster than in the past. The quality of work seemed to be very good. There is some problem with a non-uniform surface appearance, but all specifications were proven to be satisfied and good performance is expected. Sealing of only the outside of the fascia girders helped to solve the possible aesthetics problem, since the public will generally only see the outside beam faces.

This project showed that the cost of metallizing is still too high to compete with traditional paint systems, if first-cost analysis is used. The bid price of $98.82 per square meter versus $21.50-$27.00 per square meter for painting tends to lean owners away from the metallizing option. However, if life cycle cost analysis is used, as recommended through bridge management concepts, metallizing can be proven to be advantageous. The estimated service life of 25-40 years without the need for touch-up can certainly compete with painting systems, provided life-cycle costs are considered. This project showed that the technology is available to significantly improve production rates, and these increased production rates should eventually lead to decreased costs of metallizing in general.