Lexington, KY - If you were a Kentucky Transportation Cabinet chief district engineer who had to make the call on how to repair a steel reinforced concrete beam under a highway that had been damaged by a wayward truck, you'd have several options.
One might be to close the bridge for months while a large crew worked to replace the entire superstructure (deck and beams) at a cost of about $600,000. The other option might be to keep the bridge open, use a small crew, with one or two people doing the repair work, and complete it for around $100,000.
To most engineers, the latter option sounds irresistible.
Taxpayers of Kentucky (and soon to include other states), a small group of researchers in a lab at the University of Kentucky is working to save you millions of dollars in road and bridge repairs.
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The repair system they've developed is called CatStrong CRP80. The breakdown: Cat, because this is Wildcat country; Strong, because it's, well, ; CRP, for carbon fiber reinforced polymer rod panels (whew) and 80, because, according to its developers, it can resist more than 80,000 pounds of force per one-foot wide section of CRP80.
CatStrong is made from small diameter carbon fiber rods formed into a kind of sheet or panel. Imagine putting up sheets of wallpaper to improve the look of a room. CatStrong panels improve the strength of a damaged beam.
The UK researchers developed CatStrong with funding from the Kentucky Science and Technology Corporation. Dr. Issam Harik, professor of civil engineering - structures and coatings - Kentucky Transportation Center, leads the team.
"The objective was to reduce the cost of the repairs because they're quite expensive, not just from the material side, but from the labor side," explained Dr. Harik. "We wanted to provide a methodology that is efficient, effective and very quick and easy to apply."
When a beam has been damaged, the steel inside the concrete has lost its ability to resist loads, namely the cars, trucks and every other kind of heavy vehicle that pass over it.
A recent demonstration of CatStrong took place over the eastbound portion of the Bluegrass Parkway in Anderson County. A beam had been struck by an overly tall truck which damaged the embedded reinforcing steel.
CatStrong was applied to strengthen the beam in place of the damaged reinforcing bars.
"The first thing we do is clean the entire surface and clear out any bad concrete. Then we fill the void with new concrete and some bonding agent. We bring the beam back as close to its original shape as possible," said Dr. Harik.
The next steps go like this: Step 1 - application of a special resin on the prepared concrete girder. Step 2 - application of the CRP80 panel on the resin. Step 3 - application of another resin coat over the CRP80.
"The advantage of this material is that it is very lightweight and just one person can apply it in a short time. It can replace the equivalent of a steel plate that weighs 25 times as heavy as CRP80," reported Dr. Harik. "The strength of the repaired beam will actually be stronger than the original beam."
The repaired section of the beam was also wrapped in three-directional carbon fabric to prevent concrete chunks from falling on cars passing under the bridge in the event of future impacts.
The panels for the bridge over the Bluegrass Parkway were assembled by students from the UK College of Engineering. Dr. Harik says he likes using students in the development and testing of the CRP80.
Speaking of another test application earlier in Carter County, Dr. Harik said that the carbon fiber material repairs "kept the bridge open and the public (living and driving) around the bridge did not notice anything unusual about it. All they know is that they have always been driving on that bridge."
You may wonder whether CatStrong could be used to repair structural cracks in the Sherman Minton Bridge, which spans Kentucky and Indiana a few miles downriver from Louisville. Cracks discovered Sept. 8 forced the bridge to be closed indefinitely, causing massive traffic delays and detours for thousands of drivers on both sides of the river.
Unfortunately, CatStrong is not the answer.
"That is a future project we are looking into. We have started some initial work. Maybe in the future we will develop a new product (for steel)," said Dr. Harik. "CatStrong is right for certain types of cracks but it may not be right for certain kinds of steel."
CatStrong stems from UK's research into composites dating back to the early 1990s. The lab has achieved a number of firsts with these materials in both Kentucky and around the world.
The small carbon rods used in CatStrong are manufactured by Diversified Structural Composites, based in Erlanger, Ky. Lee Burch, senior vice president of operations, said his company's role at the moment is as a supplier but he hopes the relationship continues in whatever way CatStrong is rolled out to the public.