industrial ecology

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N.J. Bridge Puts Recycled Plastic to Unusual Use
Combination of Two Petrochemicals May Offer Inexpensive and Durable
Alternative to Wood, Steel and Concrete

By Louis Jacobson
Special to The Washington Post
Monday, December 8, 2003; Page A09


NEW BRUNSWICK, N.J. -- A plastic bridge sounds like something that belongs
in Legoland. But in southern New Jersey's Pine Barrens, a 56-foot-long
bridge crafted from recycled soda bottles, coffee cups and similar refuse
has been carrying traffic over the Mullica River for more than a year.

Although the Rutgers University scientists who invented the novel plastic
material used to build the one-lane bridge acknowledge that their
technology is not yet ready for use on heavily traveled spans, such as
those in the interstate highway system, they say plastic has quickly
exceeded their expectations as a bridge-building material.

Most notably, they say, their plastic is already technically and
economically competitive with wood, which is used in more than half a
million bridges in the United States today.

As long ago as the mid-1970s, the Federal Highway Administration began
encouraging and funding research into bridges with decks made of lighter,
yet equally strong, fiber-reinforced plastic composites. These systems,
often made of glass fibers and polyester or vinyl-based resins, are still
in use, FHWA engineers say. The bridges developed by Rutgers, by contrast,
represent a breakthrough: They are plastic through and through.

"I don't know that this is interstate bridge material at this point, and I
don't know whether or not it will ever be, but it's perfect for replacing
smaller wood bridges," said Richard G. Lampo, a materials engineer at the
Construction Engineering Research Laboratory of the U.S. Army Corps of
Engineers Research and Development Center in Champaign, Ill. Lampo, who
has advised the Rutgers team, said he recently visited the New Jersey
bridge and was impressed with how the structure was holding up.

Thomas J. Nosker and Richard W. Renfree, the Rutgers engineers, came up
with their plastic unexpectedly. They had been experimenting with two
common kinds of plastic: high-density polyethylene (HDPE), which is used
to make such items as milk containers and detergent bottles; and
polystyrene, which is commonly used in coat hangers and disposable eating
utensils.

Neither material alone is suitable for making bridges. HDPE is not stiff
enough, and polystyrene, while stiffer, is too brittle. At the time the
two researchers were doing their experiments, nothing suggested that the
combination of these two plastics would make a more promising material.

But Nosker and Renfree found that one combination -- 65 percent HDPE and
35 percent polystyrene -- worked unexpectedly well. With the help of
Washington and Lee University engineer Kenneth Van Ness, the Rutgers team
figured out why. It turned out that the polystyrene, when added to a
cooling batch of HDPE in the proper proportion, fills the voids in HDPE's
sponge-like structure and stiffens the material considerably.

Though Nosker and Renfree made this discovery in 1988, their finding
attracted little attention for almost a decade. But they persevered, and
around 1996, they began to zero in on bridge construction as the most
promising application.

In 1999, Nosker and Renfree oversaw construction of a part-plastic,
part-steel bridge in Missouri and, two years later, of a part-plastic,
part-fiberglass bridge in New York. Then, around Thanksgiving of 2002,
they completed the bridge over the Mullica. Unlike its two predecessors,
the Mullica bridge was made entirely of plastic, except for zinc-coated
steel fasteners and the wooden piles, which were still in place from the
bridge's wooden predecessor.

Building the 36-foot-long bridge, plus 10-foot abutments on each side, was
so easy that it took "11 days for three PhDs, one maintenance guy and a
few helpers to do it," Nosker says. The price tag, paid by the New Jersey
Department of Environmental Protection, was $75,000 -- far less,
transportation experts told Nosker at the time, than the $350,000 a
conventional wood bridge might have cost. And the plastic bridge has the
added bonus of safely and creatively disposing of solid waste.

The New Jersey bridge, they say, weighs half or less of what an equivalent
wood or metal-and-concrete bridge would weigh -- the plastic logs even
float -- yet it is just as strong, they say.

Plastic is also safer for the environment, Nosker says. Wood used in
construction is typically treated with chemicals that keep insects away,
but many states have banned some commonly used treatments because of
concerns that they contribute to environmental pollution.

In addition, plastic does not have to be cut from irregularly sized logs
into precise shapes. It can be easily molded into any form desired.

Plastic also needs less maintenance than wood, metal or concrete. Bugs
have no interest in eating plastic beams, and plastic does not need to be
painted.

For the New Jersey bridge, an Edison, N.J.-based company called Polywood
Inc. -- a licensee of the Nosker-Renfree technology -- created I-beams.

The big question is how well plastic bridges will stand up to years of
traffic, said Myint Lwin, director of the federal Office of Bridge
Technology. "There is no credible, currently available way to predict 50
to 75 years of structural performance from short-term material test data.
The most reliable method now available to predict performance over the
long term is the straightforward -- and slow -- method of constructing a
bridge made from the material and monitoring its condition over its
service life."

That said, the FHWA "sees a tremendous market potential" for new
bridge-building materials that involve plastics, Lwin said. The agency's
Innovative Bridge Research and Construction Program has sponsored 44 other
projects involving experimental plastic composite bridge-deck systems.

The professors and Polywood are encouraged by the modest success of the
company's plastic railroad-tie business. While plastic ties account for
less than half of 1 percent of railroad ties in use nationally, sales to
railroads and transit agencies have been growing in recent years.

For the company, the Mullica River bridge was a key advance, since it
demonstrated that plastic bridges can be cheaper than wood bridges.
"Breaking into a 100-year-old industry takes a while," said Marc Green,
Polywood's chief financial officer.