The latest in bridge construction technology goes unnoticed by drivers zipping over a two-lane highway that carves through the countryside of central Maine.
The 35-foot-long Neal Bridge on Route 11 is the first in the nation to use a process developed at the University of Maine that's dubbed "bridge in a backpack" because the materials used to make the arches can be carried to the site in duffel bags.
Once at the site, a light, durable fabric that folds as easily as a pair of pants is filled with concrete to form arches that will support the span. They're installed in a matter of days or even hours, instead of weeks. The process is being touted as a way to cut costs and lengthen the life expectancy of bridges.
"Instead of having problems in 20 years, you won't have problems until 40 years," said Habib Dagher, director of the university's Advanced Structures and Composites Center. "This could be 100-plus years of performance."
Contributing to the interest in higher-performing bridges was the collapse of the Interstate 35W bridge - a 40-year-old steel-supported structure in Minneapolis - which killed 13 people and injured dozens during rush hour on Aug. 1, 2007.
"Everybody is much more aware today of our decaying infrastructure and our need for involvement," said Brit Svoboda, president of a Florida company that hopes to commercialize the concept.
There are thousands of highway bridges in the U.S., virtually all of which are made of concrete or steel. But when it came time to replace the 70-year-old Neal Bridge, the Maine Department of Transportation decided to try the new method.
University workers put together 23 fabric arches that were cut to a pattern, inflated and coated with resin to retain their shape, Dagher said. They were then taken to the site, put into place and filled with concrete - all in a day.
The fabric is made of composite materials, often a blend of carbon or glass fibers, which reduce construction time and costs, Dagher said.
After the arches were installed, a lightweight deck was bolted on top of them and covered with sand. Asphalt was then laid on top of the sand.
The department plans to build six more bridges in the next two years using the same technology. On future projects, the arches will be rolled up and carried in gym-style duffel bags in the backs of pickup trucks, then inflated at the construction sites.
Much of the on-site preparation work will be eliminated, and trucks won't be needed to haul heavy beams. Concrete trucks still would be needed, though, for filling the inflated arches.
The materials have been making inroads in both bridge construction and repair, said John Busel of the American Composites Manufacturers Association in Arlington, Va.
But the idea of building bridges with composite arches that are inflated on site is new. It'll take time to convince bridge designers and government transportation officials that the approach is viable, he said.
That's what has happened with other products. Light, strong and corrosion-resistant, composite materials are now used in hundreds of everyday items from golf clubs to boats to cars.
"Slowly and surely it's happening," Busel said.
The materials also have been shown to significantly outlast steel or concrete because they don't corrode. Testing has shown that bridges made out of composite materials could last twice as long as concrete or steel bridges, Dagher said.
The idea has caught the attention of two business partners in Florida, who formed a company called Advanced Infrastructure Technologies LLC to take the concept to market.
The company has been hearing from engineers and state transportation officials who are interested in learning more, said Svoboda, the CEO and president, from his office in Naples, Fla. The firm expects to spend $8 million to $10 million in the next couple of years on the project, he said.
Peter Vigue, chairman and CEO of the Cianbro Cos., said the approach provides advantages in construction speed and cost, especially for smaller bridges. Cianbro has construction projects in about 15 states in the Northeast and Mid-Atlantic.
The biggest obstacle for it to catch on is convincing bridge designers and state transportation officials that it's a viable approach, he said.
"It's incumbent on people in the industry to build better structures that can be done faster and in a less expensive way," he said. "I think this is one of those potential solutions."