A bridge-building method developed by the University of Maine uses lightweight carbon tubes to make arches as strong as steel.
Construction is under way on Maine’s seventh — largest — high-tech bridge, replacing standard concrete and steel construction with a lightweight and portable carbon-fiber tube structure. The new technology is designed to ward off corrosion, double a bridge’s structural lifespan and significantly reduce construction time and repair costs.
At an offsite location, carbon-fiber tubes are inflated, shaped into arches and infused with resin to harden them. The tubes are then moved to the foundation’s location and filled with concrete, producing arches as strong as steel. The arches are then covered with a fiber-reinforced decking and buried under several feet of sand.
The carbon fiber protects the resin from harsh weather and extreme climates, which safety experts say is the greatest cause of bridge corrosion. In standard steel bridge construction, de-icing road salts and saltwater infiltrate the concrete and corrode the steel bar, which causes it to expand and crack the concrete, weakening the bridge.
The new, environmentally-safe design was developed by the University of Maine Advanced Structures and Composites Center and has been named “bridge in a backpack” technology because its components are lightweight and easily transportable.
“It changes the entire logistics of the construction,” said Habib Dagher, a University of Maine engineering professor and director of the Advanced Structures and Composites Center, which brings new technology to construction sites. A 70-foot arch weighs about 200 pounds, compared to a steel girder, which weighs between 40,000 and 50,000 pounds, he said.
The new technology could be one way to help rebuild the country’s bridge infrastructure, which has scored poorly in recent years on an annual report card of their integrity. A national conversation about bridge safety continues, a debate first sparked in 2007 after the I-35 Minnesota bridge over the Mississippi River, killing 13.
Although the concept sounds simple and quick — in two months, seven bridges have been built throughout Maine, including one bridge that was completed in 12 days — the design took eight years of development and testing.
“There was a lot of homework done before we got out there,” Dagher said.
Inside an 85,000-square-foot lab, University of Maine researchers built five bridges and simulated traffic using a computer system that can “add” hundreds of thousands of pounds at a fast pace onto the bridge, similar to the weight of real-life bigrigs.
“We tested the strength of the bridge after 50 or 75 years of aging versus the strength of the bridge without being aged, and we saw essentially no degradation over the system,” said Dagher.
The testing and design development were funded by the Federal Highway Administration and the Army Corps of Engineers.
After the I-35 Minneapolis bridge collapsed in 2007, Maine Gov. John Baldacci signed a bill to increase the state’s bridge funding, which is spent on rehabilitating corroded bridges that have been worn down by various environmental factors.
“It’s hundreds of billions of dollars a year in infrastructure issues that we have. So by going to these new technologies, we are preventing a lot of these corrosion issues that we see out there,” said Dagher.
The costs to build the bridge are competitive with standard bridge construction, but Dagher said those costs will drop in the next year because the company has been “overbuilding” the bridges to make sure they are safe.
Dagher said it’s predicted that 20 to 30 more “bridge in a backpack” spans will be built next year both domestically and internationally, And potentially more could be in the works since the American Association of State Highway and Transportation Officials, the agency that puts out U.S. bridge codes, decided to promote the technology nationally by aiding at least eight states in building these bridges in the next couple of years.
Currently the Maine Department of Transportation has a contract for six bridges to be built in two years, and the rest of the projects have been funded by private companies.
Dagher’s team is currently in talks with Russia about using the “bridge in a backpack” technology as the country builds the infrastructure for the 2014 Winter Olympics.
“It’s a huge deal,” said Dagher. “With this technology, you can ship a dozen bridges in a 20-foot container.”