A new recycled plastic bridge at the U.S. Army¹s Fort Leonard Wood Post in Missouri, attests to the greatly expanded potential for recovering a solid waste in the U.S. while providing an alternative to conventional wood construction. Completed in June, the bridge spans a creek on Fort Wood¹s Gammon Field and represents the reuse of some 13,000 lb of mixed plastics that had been otherwise destined for a landfill.
"This construction was significant in that, while larger-sized structures have been built using recycled plastic lumber, no other known structure has the structural capacity of this bridge," said Richard Lampo, researcher at the U.S. Army Construction Engineering Research Laboratories (CERL), which led the project to build the bridge.
The recycled plastic bridge replaces an older wooden bridge at Fort Wood.
The 25-ft x 26-1/2-ft. wide structure sits on the six steel beams that had supported the original bridge and was designed to accommodate loads equivalent to light vehicles.
"I drove my half-ton pickup truck over it," said Stan Martin, civil engineering technician in Fort Wood¹s Directorate of Public Works (DPW). "The bridge looks great. It looks just like a painted wooden bridge until you get up close and see that it's plastic."
A joint effort
The bridge was built with donated materials under a joint project involving CERL, the U.S. Environmental Protection Agency (EPA) and Fort Wood's DPW.
McLaren Consulting designed the bridge using a protocol they developed for recycled plastics in coordination with the American Society for Testing and Materials and the Plastic Lumber Trade Association (PLTA). The safe capacity of the new bridge is more than 30 tons over the entire structure.
"The railings meet code requirements while deflections and dynamic response are well within accepted limits for this type of bridge," said Malcolm McLaren, president of M.G. McLaren.
Advantages of recycling
Over 8.4 billion lb of plastic containers are produced each year in the U.S., with some 6 billion lb landfilled as waste. Recognizing the environmental and potential economic benefits of reusing some of the waste plastic, several entrepreneurs started making plastic lumber and timber products.
"Historically, markets for mixed plastics have been weak, which has greatly limited recycling of these materials," said Terry Grist, environmental protection specialist at the EPA Headquarters' 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, the EPA and a group of 11 plastic lumber manufacturers to improve product quality and develop standards and specifications for the materials. CERL's interest was to infuse this environmentally friendly technology into the Corps' military and civil works construction.
Recycled plastic lumber offers a replacement for wood products, many of which are treated with chemicals, to resist rot and insect attack.
"We have wooden bridges and they're a maintenance problem," said Fort Wood¹s 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 bridges are on running or hiking paths so the splinters and loose fasteners become a safety hazard." Martin estimates that bridges made with 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, maintenance-free service life for the recycled plastic lumber bridge although the steel supports may need repainting.
Under a watchful eye
Fort Wood's DPW and CERL will continue to monitor the bridge's performance. By successfully demonstrating recycled plastic lumber in a large-scale, structural application, the project opens up potential for diverting waste plastics to beneficial use and the supply of raw materials is virtually limitless.
"It would take 87 miles of a bridge the same width as this one to use up just one year's landfill plastics," Lampo said, or the equivalent of 462,500 bridges sized like the one at Gammon Field. "We're not going to run out of raw materials any time soon."
According to McLaren, "The challenge is to promote the acceptance of these materials within the regulatory, design and construction communities. I believe the future of our industry demands the use of alternate materials for construction and the use of discarded materials is an obvious benefit to society."
