Site gives shape to ‘bridge-in-a-backpack’

Posted Feb. 20, 2009, at 8:44 p.m.

ORONO, Maine — It’s lighter, stronger and faster.

“It’s never been done before,” said Habib Dagher, the AEWC director. “When you do something that’s never been done before, to be able to make a bridge essentially from a backpack, it changes the way we build bridges.”

The technology was tested last fall with so far successful results at the Neal Bridge in Pittsfield. The 70-year-old bridge was replaced with the AEWC’s inflatable arches and opened in December as the only bridge of its kind in the world.

AEWC’s bridge technology has caught the eye of Advanced Infrastructure Technologies, a newly formed investment group that announced on Friday plans to invest money to market the center’s “bridge-in-a-backpack” concept. The AEWC is working with Brunswick-based Harbor Technologies on another bridge technology, which entails horizontal girders made of concrete enveloped in a composite material.

Although the two products differ, the advantages are similar, according to the AEWC.

The materials are lighter, which means heavy placement and transport equipment isn’t necessary. The composite materials and fibers are as strong as steel. And the whole process is quicker — once the materials are fabricated and the site is ready, construction time takes a matter of days rather than weeks or months. That means shorter road closures and traffic diversions.

The Neal Bridge cost $581,000, which Dagher said is comparable to the cost of a standard bridge.

Dagher said he hopes the cost eventually will be 20 percent less than for a standard bridge, but the money spent will have a greater impact. The center believes the typical 40- to 70-year life span of a concrete-and-steel span can be extended two or even three times, which means bridges will have to be replaced with less fre-quency.

“There’s a real opportunity here to change the way we do things for the first time,” Dagher said. “That’s why there are investors interested in this technology, and they want to start the business in Maine to manufacture these things.”

AIT’s interest is in the composite center’s “bridge-in-a-backpack” concept.

It’s not a whole bridge in one bag — rather, it’s the materials for one arch of a bridge that fit into a hockey equipment-size duffel bag.

The process starts with flat, hollow tubes made of carbon fiber that can be rolled up and fit into a bag. When the bags arrive at the work site, the tubes are unrolled and placed on a steel formwork built to the length and curvature specifications required for the bridge arch.

The tubes are inflated, taking on the shape of the formwork, and the carbon-fiber material is infused, using a vacuum process, with a vinyl ester resin. The resin is allowed to dry overnight to a strength the AEWC claims is two times stronger than steel, giving the tubes the strength and stiffness to carry the weight of the concrete. UMaine has patents pending on the technology and will license the patents to AIT.

For the building of the Neal Bridge, the arches were put together at the AEWC lab in Orono and taken to Pittsfield.

Once dry, the arch-shaped tubes are light enough to be lowered into place with a simple boom and manual labor.

When the arches are in place, they’re filled with concrete through a hole at the top of the arch. It took about an hour to fill 23 arches at the Neal Bridge.

As the concrete cures, the carbon-fiber tube becomes a skin around the concrete, and the bridge can be completed. Workers added concrete around the footing of the Neal Bridge arches, covered the arches in a corrugated composite material, used a composite to form the deck, filled in the area with dirt and sand, and paved the deck. The bridge is due for one more paving this spring.

The benefits of the new technology are threefold, Dagher said. First, the arches are an instant framework. Second, no steel reinforcing bars, or rebar, are needed because the tubes are stronger than steel. Third, the tubes protect the concrete from water and elements, therefore extending the life of the concrete.

“You know what happens to concrete and rebar with the environment in Maine,” Dagher said. “Water gets in there and it cracks, it freezes, and breaks up the concrete. Now water can’t get in there. The concrete is completely protected from the environment so bridges can last quite a bit longer.”

Sand and dirt will help protect the concrete footing from road salt and other corrosive materials.

The bridge-building process takes around two days, not counting demolition and construction, depending on the size of the bridge. The Neal Bridge, which is 44 feet long and 35 feet wide, took 23 arches with a diameter of 12 inches and span of 35 feet apiece.

The other bridge technology, which the AEWC is working on for Harbor Technology, involves horizontal girders made of composite material that originally was developed for harbor pilings.

Like the arches, the girders also will be a form for concrete. Each box-shaped girder is made of composite material with an arch form buried inside. Concrete is pumped into the form. Once it’s cured, it’s ready for use.

The AEWC has now in its lab a 70-foot girder to test for durability on a computer-controlled actuator that can simulate 50 years of highway vehicle traffic in about a month. There are sensors on the bridge by which staff can monitor the bridge during testing.

Dagher said similar testing was done on the arch technology and no reduction in strength was found.

If the testing goes well, the Maine Department of Transportation has agreed to build a 500-foot bridge in southern Maine using the AEWC’s girders, as well as six more bridges throughout the state.

“It’s a great example of how research at the university starts as ideas born in this laboratory and then all the testing is done, and now the industry has taken an interest,” Dagher said. “It’s an example of how research and development, a perfect example of R and D taking off.”

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