Sparsely populated Huron County, Ohio, with just 60,000 residents and 495 square miles of land, has approximately 400 vehicular bridges.
One of them is made of plastic.
Made of fiberglass-reinforced vinyl ester, the rural bridge installed last fall is just 17 feet long, requiring just a half-second to cross it at 20 miles per hour, but is typical of the many rural bridges that pepper virtually every slice of the U.S.
Bridge construction remains a niche application for plastics, but considering the number of bridges in every county, in every state, and beyond, it is a niche with an enormous amount of market potential.
And that is precisely the way it is being viewed by companies manufacturing structural lumber commercially, and those in academia and the engineering community who are applying plastics in various bridge projects throughout the country.
According to the Department of Transportation's Federal Highway Administration Web site, there are at least 62 thermoset FRP bridges installed in the U.S. There are untold numbers of plastic bridges made from recycled thermoplastic material as well.
Of the plastics manufacturers and engineering groups working on plastic bridge design and construction, two groups stand out. The first is the group responsible for the type of bridge found in Huron County. Those fiberglass-reinforced vinyl ester panels were manufactured by Kansas Structural Composites Inc. in Russell, Kan., under CEO and President Jerry Plunkett, who could not be reached for comment.
Several engineers and researchers have been working with KSCI and funding projects through grant money from the FHWA.
The more-publicized, second group is based at Rutgers University in Piscataway, N.J. The school's Center for Advanced Materials via Immiscible Polymer Processing is perhaps the epicenter of emerging plastic lumber technology.
The technology uses 100 percent recycled content about two thirds post-consumer polyethylene bottles and one-third automotive bumper scrap to extrude I-beams and T-beams designed to replace steel and wood in bridge applications.
In 2003, the world's first all-plastic bridge opened in New Jersey's Wharton State Forest using the beams, which then were made by Polywood Inc. of Edison, N.J., and now are made by Basking Ridge, N.J.-based Axion International Inc.
Last month, the U.S. Army drove an M1 Abrams tank weighing more than 140,000 pounds across a newly constructed span near Fort Bragg, N.C.
It's four times as hard to hold up a tank as a semi, said Thomas Nosker, principal researcher for the advanced materials center at Rutgers.
The bridge was designed by West Nyack, N.Y.-based McLaren Engineering Group. The design was funded by the Department of Defense's Corrosion Prevention and Control Program, and its construction and load testing was paid for by the Installation Technology Transition Program.
The bridge is 36 feet long and is made from 170,000 pounds of recycled gallon milk jugs about 1.1 million containers. A wood bridge would weigh three times that much, require more fasteners and take three times as long to build, officials said.
Most importantly, he said, the plastic bridge is less expensive than a wood counterpart.
This thermoplastic bridge, able to withstand heavy loads with little to no maintenance [and] expected to last at least 50 years, is no longer the bridge of the future it's the bridge for today, Daniel Dunmire, the Secretary of Defense's director of corrosion policy and oversight, said in a U.S. Army news release.
It also meets national environmental goals of being completely recyclable. This technology is not only good for [the Defense Department], but should be immediately transferred to state departments of transportation for use with short-span bridges wherever possible.
Cost has long been the biggest hurdle faced by structural plastic lumber manufacturers trying to introduce their products to the market.
And that's where the attitudes and outlooks of the two groups actively building plastic bridges seem to diverge. To date, composite panel manufacturers have not found a way to build a plastic bridge more cheaply than they could build one of wood or steel.
As for the bridges, the people working with them seem to be impressed with the structures' performance in the field.
Right now, we have seen nothing but good, said Joe Kovach, Huron County engineer. It's performing way better than we thought. When we first started this thing, I specifically picked a small little bridge in case it failed.
We went into it and I started meeting the various players. These guys are truly professional. They never thought they would fail. They brought me around. This thing will outlast us all.
The composite panels are only 15 percent solid, and feature a honeycomb design as the key to their structural strength. The panels are so strong the group had trouble cutting it, Kovach said.
We had a diamond-bit chain saw. We couldn't cut it in half. We had to send it to a stone mason that cuts slate, he said. We might have created something you can't destroy.
Bedford, Pa.-based Bedford Reinforced Plastics Inc. provided the bridge deck material for a 2001 bridge project in Wheeling, W.Va., supervised by Hota GangaRao, director of the Constructed Facilities Center at Morgantown-based West Virginia University.
Not a crack, GangaRao said of the now 8-year-old, 210-foot steel-supported span. It's doing very nicely.
Plastic faces the same obstacles as any new construction material introduced to an established market.
Economics continue to be at the forefront of the discussion.
I hate to say it, but I honestly think due to the price difference, it's going to remain a niche material for a significant amount of time, said Dave Meggers, research and development engineer for the Kansas Department of Transportation.
Companies and engineers working with less-expensive recycled polymers said the technology is here, repeatable and affordable. Engineers working on military bridge projects have data on how much some military bases spend annually to maintain wood bridges.
With that information we started thinking, gee, life-cycle cost is great, and it's an important consideration, but far too often it's the first cost that still rules decision making, said Rich Lampo, a materials engineer with the U.S. Army Corps of Engineers' Engineer Research and Development Center in Champaign, Ill. We kept thinking about how we could design and construct [it] to make it cost-competitive on a first-cost basis.
When the M1 Abrams tank drove across the bridge, the group knew they had done just that.
There are hundreds of these timber bridges on military installations, Lampo said. And there are hundreds and thousands throughout the country. There's tremendous market here.
Cost aside, the initial concern is safety.
Normal people don't think about how serious county engineers and bridge engineers take loss of life, said Douglas Nims, an associate professor of civil engineering at the University of Toledo in Ohio. In a typical year, about 12 people die from bridge failures. It's not a socially acceptable thing to have happen.
Nims and a group of UT graduate students have taken the lead in the testing efforts of the new Huron County bridge. Nims said the manufacturing process needs to be repeatable.
There is not a standardized way to design them, he said. The process needs to be repeatable. The whole standardization and quality manuals need to be generated.
GangaRao said the onus is on the American Association of State Highway and Transportation Officials to develop standards for the industry. The group has seemed reluctant to do so thus far, he said.
Lampo said the goal with the Army is to standardize bridge design for military bases.
We still need to document all these benefits, he said. And I really think if this is truly beneficial, then we need to pass this along to organizations like AASHTO, which is responsible for bridge designs.
I've been building bridges for more than 10 years out of this stuff, Nosker said. And none of these things fail in the field. None of them. There's a pattern.
The real issue, Rutger's Nosker said, is designing the bridges to withstand long-term creep.
I can take a tank and park it on that bridge for 25 years, drive it off, and the bridge will go back to the original shape, he said.
The use of recycled material gives Axion and the Rutgers researchers a definite edge, he said.
Plastic resin prices are going to continue to go up, he said. Prices of oil and petroleum products are going to go up. It's not cheap to make [bio-based plastics] from renewable resources. What there is, is plenty of opportunity in the post-consumer plastics market.
The real challenge is for [the plastics industry] to figure out how to make better plastics for less money. And guess what? It's possible.
Nosker said he envisions a future where the best bridges are constructed using a combination of his technology and thermoset resins like those used in fiber-reinforced panels.
And he's not willing to settle for just small-span construction.
There is no physical limit to the size you can make these structures, he said.
Meggers, of Kansas' DOT, concurred that cooperative innovation will be the key to moving the technology forward.
We're going to sit back here and keep moving along slowly, he said. When you see that many people looking at it, you get the idea it's a reasonable idea and that it's going to turn viable at some point.
The fact that it keeps coming up shows that it is viable and that there is substance to it. Innovation and design that's what's going to do it. It's just going to take the right time and the right opportunities.