BELFAST, Maine — The stretch of Herrick Road now under construction at the Little River is decidedly bucolic, with llamas grazing peaceably in nearby green fields and the river flowing gently to the city reservoir.
But the bridge that started to take shape across the river Wednesday to replace the worn-out 1921 structure is at the cutting edge of technology.
When completed, the 48-foot-long arch of concrete-filled carbon-fiber tubes will be the largest “Bridge in a Backpack” constructed in Maine. It should last much longer than a typical steel or concrete bridge and essentially eliminate bridge maintenance, according to Project Manager Nate Benoit of the Maine Department of Transportation.
“Right now, we’re in the process of further developing the technology,” he said. “With experience, we expect to come up with more innovative ways to use the tubes and to decrease construction time.”
Wednesday afternoon, the construction crew from Stetson & Watson contractors of Pittsfield appeared to easily maneuver the long but light tubes into place across the river to make perfect arches. Altogether, 16 of the tubes will be placed and filled with concrete to make the bridge, according to Bob Schmitt, a representative of Advanced Infrastructure Technologies, the Orono company that is licensing the new composite technology invented at the University of Maine Advanced Structures and Composites Center.
The Bridge in a Backpack, which was introduced by center director Habib Dagher in February 2009, uses carbon-fiber tubes that are inflated, shaped into arches and infused with resin before being moved into place. The tubes then are filled with concrete, producing arches that are harder than steel yet resistant to corrosion. Finally, the arches are overlaid with a fiber-reinforced decking and buried under several feet of dirt and sand.
When deflated, each bridge arch fits into a sack roughly the size of a hockey equipment bag — hence the Bridge in a Backpack moniker — which makes for easy transport.
Officials have touted the technology as being cheaper, easier to install, longer lasting and better for the environment than traditional bridges, but Benoit said that the Belfast bridge is “cost competitive” with a traditional structure.
Between the $873,167 low bid from Stetson & Watson and the $245,000 needed to purchase the tubes from AIT, the project will cost a total of $1.1 million, he said.
It won’t be completed until June 15, 2011, but the road over the river should be open to traffic by Thanksgiving.
The bridge is the third of six backpack bridges to be constructed through the DOT, which is responsible for all bridges longer than 20 feet on local roads in the state. The project began after a Minneapolis bridge collapsed in 2007, and Gov. John Baldacci signed a bill to increase Maine’s bridge funding. An increase in vehicle registration fees has added an extra $40 million per year for four years to the state’s bridge budget, Benoit said.