Bridges made from recycled plastics can support weight of tanks

15-Oct-09

New bridges made from recycled detergent bottles and car bumpers are strong enough to hold up a 73-ton Abrams tank, takes only a month to build, costs 25% less than an equivalent wooden bridge and requires no annual maintenance. It was easy to make the bridge by using a special blending process and forming the plastic into I-beams. Rutgers University professor Tom Nosker began developing plastic bridges, lumber and railroads ties in the 1980s. The plastic bridge starts out as a hot tank of liquid polyethylene, derived from plastic melted down from empty detergent bottles. Liquid polystyrene and fiberglass from car bumpers are thrust into the polyethylene, and then the mixture is formed into whatever shape is needed. As the polyethylene cools, it shrinks, locking the polystyrene and fiberglass into place and providing certain flexibility for the structure. The polystyrene and fiberglass then harden, providing strength for the materials. The process sounds easy enough, but it's actually quite complicated, says Ken Van Ness, a scientist at Washington and Lee University in Virginia who helped create the plastic construction materials. Like oil and water, polystyrene and polyethylene usually don't mix; they tend to form large clumps. Only under special heating conditions will the two plastics form materials strong enough to hold a tank. Once the plastic pieces have been created, they are assembled on site in about a month, using about 60,000 pounds of polyethylene from detergent bottles and 30,000 pounds of fiberglass-infused polystyrene from car bumpers. A steel and concrete bridge, on the other hand, could take months to build if multiple layers of concrete need to be poured and cured. Faster construction and cheaper materials saves the Army money. So will fewer annual inspections. The plastic bridge needs virtually no annual maintenance. Steel, concrete and wooden bridges all require some kind of annual upkeep. The U.S. Army estimates that its return on maintenance costs will be 34 to 1 with a plastic bridge. Considering the U.S. Army spends an estimated $5.8 billion each year preventing infrastructure corrosion, that's a lot of dollars saved.