The Center for Plastics Recycling Research has bridged a gap in the use of plastic lumber with a new way to build bridges. The center developed a way to overcome the lack of stiffness of plastic lumber in comparison to wood, when it designed and built the structural members of a 32-foot-long, 6-feet, 8-inch-wide footbridge due to be installed at the Tiffany Street Pier project in New York City.
``The Tiffany Pier project utilized plastic lumber, made from recycled mixed plastic scrap for the pier and seawall,'' said Richard Renfree, assistant research professor at the center.
``Our part,'' he noted, ``has been to make the footbridge, which will give access from the public area to the pier.''
The problem facing the center's researchers was to develop a technique that would render ordinary plastic lumber as stiff as wood, something that has not been done before without significant external supports.
``Using normal plastic lumber techniques, you would have to have pilings and flat beams, such as you would have with wood, and the weight-bearing capabilities of the plastic would not be as good as wood. One of the problems with plastic lumber is that it bends and sags through time,'' Renfree said.
``But we figured if you could take advantage of the fact that one of the natural tendencies of plastic lumber is to bend, we could build a bridge with less material, and at less cost.''
Tom Nosker, assistant professor of ceramic engineering at Rutgers, developed a way to bend the bridge's structural supports into an arch shape, without remelting and weakening it. The researchers took 38-foot, 6-by 8-inch plastic lumber boards, cut them at both ends, attached cables and bent them into an arch using compression.
With the technique, the load-bearing capacity of the plastic was increased greatly relative to its stiffness, eliminating the need for other structural supports. The four arches are kept from bending any more by cables, and the entire support structure of the bridge was built with four pieces of plastic lumber.
``This obviously cuts the cost of materials, either of plastic lumber used in a traditional way, or of wood,'' Renfree said. ``And when the planking and hardware is added to finish the structure, the total cost will be only $4,000. It is much less than you would pay for a wood bridge of the same size.''
Trimax Plastic Lumber of Ronkonkoma, N.Y., provided the plastic lumber for the bridge. A number of other companies contributed to the overall, 480-foot-long, 50-foot-wide Tiffany Street Pier project.
The U.S. Army Corps of Engineers, which provided some funding and development help for the entire Tiffany Street project, will move the structure from Rutgers to the Bronx to be installed.
The New York City Department of General Services will do the installation.
CPRR is a research and development arm of the State University of New Jersey (Rutgers), in New Brunswick, N.J. The center was founded in 1985 at Rutgers with the sponsorship of the Plastics Recycling Foundation to research and develop methods for collecting, sorting and reclaiming waste plastics.