Plastic lumber bridges the gap at army base

Bridge project shows the potential for recycled plastic to replace wood in some applications.

RECYCLED plastic bridge at Fort Leonard Wood in Champaign, Illinois demonstrates a promising alternative to conventional wood construction. Completed last summer, the bridge spans a creek on the Army post's Gammon Field, representing reuse of some 6.5 tons of mixed plastics once destined for a landfill. "This construction is significant in that, while largersized structures have been built using recycled plastic lumber, no other one is known to have the structural capacity of this bridge," says Richard Lampo, researcher at the U.S. Army Construction Engineering Research Laboratories (CERL), which led the project.

The recycled plastic bridge replaces an older wooden one and will bear mostly foot traffic. Standing 25 feet long by 26.5 feet wide, the structure sits on six steel beams that had supported the original bridge. "I drove my half-ton pickup over it," says Stan Martin, civil engineering technician at Fort Leonard Wood's Directorate of Public Works (DPW). "It just looks like a painted wooden bridge until you get up close and see that it's plastic."

The bridge was built under a joint project involving CERL, the U.S. Environmental Protection Agency (EPA) and Fort Wood's DPW. Also participating were Battelle in Columbus, Ohio, the Plastic Lumber Trade Association (PLTA) in Akron, Ohio, and Rutgers University. Four companies donated materials.

DESIGN AND CONSTRUCTION

The bridge was designed by McLaren Consulting Engineers using a protocol developed for recycled plastics in coordination with the American Society for Testing and Materials and PLTA. Materials for the bridge construction were selected according to their mechanical properties. The plastic lumber was composed predominantly of high-density polyethylene. The joists and railing posts had polystyrene added to the formulation to increase the stiffness of the boards based on their intended use.

Over 4.2 million tons of plastic containers are produced each year in the U.S.; about three million tons are landfilled. "Historically, markets for mixed plastics have been weak, which has greatly limited recycling of these materials," says Terry Grist of the EPA's Office of Solid Waste. "The success of projects such as this one will serve to open up new markets for these materials and provide the opportunity to increase the overall recovery rate for plastics."

CERL has been working since the early 1990s with Rutgers University, EPA, and a group of plastic lumber manufacturers to improve product quality and develop standards and specifications for the materials. Its interest was to infuse this environmentally friendly technology into military and civil works construction.

PLASTIC LUMBER ADVANTAGES

Recycled plastic lumber offers a replacement for wood products, many of which are treated with chemicals to resist rot and insect attack. Treated wood can require special handling because chemicals can leach into the environment if not disposed of properly. Wood structures not treated with chemicals have to be maintained periodically by coating with preservatives that can release organic volatiles into the atmosphere. Plastic lumber requires no such maintenance.

"We have wooden bridges and they're a maintenance problem," says Fort Wood's Martin. "We have to send crews out two or three times a year to replace deteriorated lumber and fasteners that have worked loose. Most of our wood bridges are on running or hiking paths, so the splinters and loose fasteners become a safety hazard."

Martin estimates that bridges made with CCA-treated wood last about 15 years under the climate and usage frequency at Fort Wood. Untreated wood bridges may have to be replaced as often as every five years. In contrast, CERL's Lampo projects a 50-year, maintenancefree service life for the recycled plastic lumber bridge (although steel supports may need repainting).

The initial cost of the materials for the bridge was 2.5 to three times what it would be for chemically treated wood lumber materials. Since there is no need for maintenance and replacement, this difference should be equalized in 8.5 years, with savings resulting over the remaining life of the plastic lumber bridge.

Resistance to moisture/water, rot and insects, as well as other advantages, make plastic lumber well suited to replace wood in damp, wet and/or insect-infected areas. The supply of feedstock is virtually limitless. "It would take 87 miles of a bridge the same width as this one to use up just one year's landfilled plastics," says Lampo - the equivalent of 462,500 bridges sized like the one on Gammon Field. "We're not going to run out of raw materials any time soon."