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Aerospace innovation gives new life to bridges
GRAYSON, Ky. -- It could have been mistaken for a beautification project: workers gluing thin sheets of a carbon fiber material to the girders of the 10-year-old Grayson bridge over Little Sandy River.
The goal is to make it stronger, long enough to last another 50 years.
The very notion of wrapping bridges in polyester-thin fabric to make them stronger may sound absurd, but a University of Kentucky researcher isn't laughing.
Issam Harik, a civil engineering professor, said the super-strong carbon fiber material may be the key to giving new life to the nation's aging bridges, of which about 30 percent are considered substandard by the Federal Highway Administration.
The Grayson bridge in eastern Kentucky, although in its infancy, was built with substandard beams -- not enough steel reinforcing the concrete, state transportation officials said. That caused it to prematurely weaken.
Harik said the state would have had to repair the entire superstructure in the next three to four years. "Cracks were growing at a fast rate," he said.
At least 50 years
Instead, workers using epoxy glued thin sheets of the carbon fiber to the girders of the 200-foot span and then coated the sheets with an additional layer of epoxy.
As a result, Harik said, the bridge is stronger than when it was first built. "Now, we are confident that it will last at least 50 years," he said.
The material, first used to strengthen the hulls of airplanes, has been slow to catch on in construction fields in the United States, where it has been available for a decade. State regulatory agencies have been slow to establish guidelines and bid specifications for engineers and contractors to follow when using the material on public projects, said Ali Ganjehlou, president of Advanced Building Materials Corp. in New York, which markets the material.
That's beginning to change as civil engineers like Harik experiment with carbon fiber, which sells for $7 to $14 a square foot.
In Georgia, transportation officials are considering draft guidelines written by Georgia Tech professor Abdul-Hamid Zureick, who has been researching the material's benefits for bridge repairs.
A bridge over Interstate 20 in suburban Atlanta was treated with the material three years ago. Zureick said the span is still standing strong.
Jim Simpson, a bridge analyst for the Kentucky Transportation Cabinet, said expanding the use of the material from aerospace applications to construction was not a giant leap.
"One of the big pluses of this fabric -- it will take any form or shape that you want it to," Simpson said. "It doesn't take its final form until it's laminated in epoxy."
'Like a fabric'
The Japanese used the material to reinforce buildings against seismic activity. In the United States, engineers quickly identified carbon fiber as a possible fix for aging bridges.
"This material is totally flexible," Ganjehlou said. "It is very thin sheets of carbon, like a fabric. It goes over any shape, any curve. Just imagine putting wallpaper on the wall. It's that easy to apply."
The strength of carbon fiber is truly impressive.
A carbon fiber thinner than a human hair will break at approximately 1 million pounds of pressure per square inch, Ganjehlou said.
In comparison, steel used in reinforcing bridges breaks at about 90,000 pounds per square inch.