Improving bridge infrastructure faster with new coating technologies

June 2013 » Features » EXIT RAMP
Connecticut DOT bridge is shown before (foreground) and after the polyaspartic coating application.

Efficiency of production is a key element of any aspect of the construction industry, especially as it relates to meeting deadlines to put infrastructure in service. The protective coatings industry has long been challenged not only to keep its own deadlines on maintenance and new construction steel bridge projects, but also to ensure that the entire chain meets or exceeds finished product expectations.

Fortunately, specifying newer technology coatings can provide improved levels of efficiency, allowing accelerated throughput and return to service not previously imaginable, and at significantly lower overall cost.

In 1960, fabricators began using zinc-rich primers to prepare the steel segments of a bridge, which were followed in the field by application of an epoxy intermediate coat and an aliphatic polyurethane topcoat as specified by the particular state department of transportation (DOT). To this day, in the minds of most bridge engineers, a bridge coating project is a three-coat operation, with return-to-service times that vary widely with the environment in which it's being applied.

But it doesn't have to be that way. Today, polyaspartic products in the aliphatic urethane family offer significant money-saving productivity improvements along with high-build, low-temperature curing, and abrasion and corrosion resistance – without the need for an intermediate coat. These coatings dry to touch in 30 minutes at 77° F, achieve a film build of up to 9 mils in just one application, and enable a return to service in two hours at 77° F. Compare this to the more typical two coats that require two eight-hour worker shifts with significant nonproductive time in between coats.

In a study conducted on an I-84 bridge, the Connecticut DOT permitted parallel spans to be painted in a comparative project. The westbound span was painted with a traditional three-part system, while the eastbound span was painted with a newer system – a moisture-cured urethane zinc-rich primer designed for low-temp application and one topcoat of polyaspartic urethane at 10 to 14 mils dry film thickness. ConnDOT engineers carefully measured time and cost for the painting of each span. Each span was prepped to SSPC SP-10/NACE 5 white metal blast. The time and effort to prepare the surface was the same for each span.

The audited results of the ConnDOT study revealed that the two-coat system was 30 percent faster to apply, which in turn reduced the need for traffic diversion by nearly a third. With the cost avoidance and reduced labor during application, ConnDOT found that the overall demonstrated cost savings was 24 percent.

Another advance in coating technology addresses the issue of holidays and pinholes in coatings in advance. It has been long recognized that the service life of a protective coating on steel is closely related to the quality of the coating application and the inspection. Now zinc-rich primers can be formulated with Navy-proven optically active pigments (OAP) that fluoresce when subjected to ultraviolet light. As a result, it is possible to identify holidays and other discontinuities during the coating application process, even during night operations, and ensure 100-percent coverage, for an extra QA/QC measure.

The new chemical painting systems of OAP primers and polyaspartic urethane topcoats have demonstrated a positive impact on profitability and faster throughput. When properly applied, the combination of these technologies provides tangible benefits and an improved bottom line through savings to all in the value chain. In the bargain come reduced labor costs, the opportunity to bid and win additional jobs, and the mitigation of job-related hazards.

Perhaps the best news of all is that before the end of 2013, gaining qualified product list acceptance for this innovation will be easier for states that participate in the American Association of State Highway and Transportation Officials' (AASHTO) program to validate new technologies, the National Transportation Product Evaluation Program (NTPEP).

Dee McNeill is regional market director (U.S and Canada), Bridge & Highway, Sherwin-Williams Protective & Marine Coatings. With 35 years of coatings experience, he is responsible for bridge and highway coating specification approval and for facilitating the development and acceptance of new technologies to protect the nation's bridge inventory.


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