Composite materials continue to penetrate into various bridge projects across the country.

A new balsa-cored composite bridge deck opened to traffic over the Pierre Part Bayou in Assumption Parish, La. The parties involved in the project included the Louisiana Department of Transportation and Development (LA DOTD), Louisiana State University (LSU), Crescent City Composites, and Alcan Baltek. The latter company says this installation is believed to be the very first balsa-cored composite deck project containing Single-Walled Carbon Nanotubes (SWCNTs).

The bridge is intended to replace traditional steel grating structures over the state’s regional bayous. Louisiana has regulations for movable bridges over waterways, and navigable water has to have at least one removable section to accommodate heavy waterway traffic. Kurt Feichtinger, technical services manager for Baltek, says composites help meet that requirement.

“For the most part, the bridges all have one span with a grid metal deck, which allows a large ship to go up the bayou by undoing the nuts and pulling the grid metal deck plates already welded to rolled steel girders and put them back later,” he said. “But, they don’t last long, so the idea was to identify an FRP solution to equal the strength, stiffness and weight.”

Half of the six 6-feet by 25-feet plates are additionally comprised of SWCNTs. This along with installed fiber optic strain gauges in the bridge panels is intended to monitor the performance of the laminate over several years. The location was chosen because it is heavily traveled by sugar cane trucks headed south to New Orleans.

Feichtinger believes this project could advance the technology in the infrastructure sector. “We’ve developed a lot of data on characterizations of laminates with single-wall carbon nanotubes,” he said. “Part of the problem is they affect the viscosity of the resin, and since these are vacuum-infused, there’s a practical limit of 0.5 percent by weight. But even that 0.5 percent by weight in e-glass, we found a 30 to 35 percent increase in flexural strength.”

Feichtinger added that as carbon nanotubes catch on and find new applications, the higher volume will drop the price lower. It is the price performance issue that remains the biggest obstacle for the technology.

Meanwhile at Fort Bragg, N.C., Axion International Holdings, Inc., Basking Ridge, N.J., constructed two 100 percent recycled plastic bridges for the US Army. The eco-friendly structural building materials used in the bridges have been specifically engineered to allow for the crossing of armored military vehicles.