West Nyack Firm Helps Make Eco-Friendly Bridge Tough Enough For Tanks

McLaren Engineering of West Nyack is part of a team named in R&D Magazine’s “Top 100 Innovations” for its work in developing the world’s first high-load “plastic wood” bridge to support heavy vehicles — including tanks.

The team of McLaren, U.S. Army Engineer Research and Development Center, Rutgers University’s Deptartment of Materials Science and Engineering and Axion International worked together to create an all thermoplastic composite bridge design. The structure had to be cost-competitive with wood or other bridge materials and meet Department of Transportation regulations.

The team’s bridge is made from recycled materials and uses an I-beam design, according to Malcolm McLaren, president and CEO of McLaren Engineering. He explained the patented mixture of composite material used for the bridge reduces the amount of material needed in each beam without compromising its structural integrity.

The design was used in a bridge installed in 2009 at the U.S. Army base in Fort Bragg, N.C., and surpassed tests by easily supporting a 70-ton fully equipped M-1 Army tank and showing a wheeled vehicle limit of 88 tons, according to McLaren.

McLaren said the team has been developing and testing all thermoplastic composite bridge designs for nearly a decade, but the breakthrough which won the team R&D Magazine’s Top 100 Innovations is that the material and design has reached the cost-competitive level.

“Our ability to successfully meet the 88-ton load level and equalizing or better wood costs means more commercial applications in short-span bridges and other high-capacity load structures beyond use on military bases,” said McLaren.  “Thermoplastic composite, better known as plastic lumber, is not a new concept. Among other items it has been used in picnic tables, decking and in lesser load-bearing structures such as foot bridges and lightweight vehicle bridges. But before our team’s work it was unheard of for high-capacity load structures,” said McLaren.

McLaren said the recognition by R&D Magazine and the success with the Fort Bragg bridge will move plastic lumber beyond just a novelty championed by environmentalists, but a viable choice for serious consideration by the construction industry for structures such as large decks, docks, seawalls, wharves and railroad bridges.

The world’s first suspension bridge using thermoplastic composite is a 31,000-pound capacity single-lane bridge in New Baltimore, N.Y., near Albany, and has shown no signs of deterioration since being built in 2000, according to McLaren. He said the Fort Bragg bridge consists of 94 percent recycled materials including glass, vehicle bumpers and some 85,000 pounds of high-density polyethylene plastic - the equivalent of roughly 550,000 one-gallon plastic milk jugs. Plastic I-beam components were used to support the heavy loads, and to provide a design that is cost-competitive to standard treated-wood bridges designed to carry the same load.

Advantages cited for the plastic wood bridges:

-       Cracks or splinters are rare.

-       It also resists rot, mildew and termites, is weather- and graffiti-resistant, and is not affected by bacteria, worms, insects or rodents.

-       Makes a good shock-absorbing surface for pedestrian traffic, requires no waterproofing, staining or regular maintenance

-       It is aesthetically pleasing. It can be manufactured to meet different design and appearance specifications. The structure also has a life expectancy of 50 years - twice as long as a treated-timber bridge.