Standing in a laboratory packed with various scientific instruments, University of Connecticut engineering professor ArashZaghi gestured to three steel beams, modest in appearance where they sit under the large and brightly-painted hydraulic-powered machine capable of applying weights of up to 275 tons.
Engineers refer to these beams as girders, a key component in bridge support. These three girders, modeled after a bridge in the Hartford area, were pressed under the lab’s hydraulic load machine until their point of failure.
But the beams themselves aren’t the most important piece in the experiment. What’s notable is the cast of concrete around one of the beams, which increased the steel's load capacity when the machine was pushing over hundreds of tons of weight into it. Zaghi said this super-strong and durable concrete could transform the way engineers across the nation approach bridge repair.
Many of Connecticut’s bridges are nearing the end of their useful lives: about a quarter of the bridges in the state have been rated as functionally obsolete, and ten percent are deemed structurally deficient. Officials say these bridges are still safe to drive on, but there’s high demand for a quick and cost-effective bridge preservation method.
One problem aging bridges face is corrosion from the elements and salt from the roads. Corrosion often occurs at the end of beams in the superstructure of the bridge -- the part that supports car traffic. Engineers usually use steel plates to patch up bridges. But that approach can be expensive and time-consuming, yielding lane closures and congestion.
Another problem with traditional infrastructure repair is that engineers and maintenance crews are still using methods that they used a half-century ago, Zaghi said.
“You don’t commute in 40-year-old cars,” Zaghi said. “The ones today are entirely different. But our infrastructure is similar to the way we were doing it 40 to 50 years ago.”
“You don’t commute in 40-year-old cars. But our infrastructure is similar to the way we were doing it 40 to 50 years ago.”
Arash Zaghi
So Zaghi, in collaboration with the Connecticut Department of Transportation, is leading a research team that's testing the tenacity of a new “super” concrete -- a mixture of chemicals and fiber that’s two to three times stronger than traditional concrete.
In the first phase of the project, the researchers had applied weight to each of the three beams in the lab to see how each held up under increased loads. The first beam wasn’t corroded. The second was. The third was also corroded, but was supported by the ultrahigh-performance concrete. That third beam, held up by a concrete cast, ended up supporting about 45,000 more pounds than the undamaged, unsupported girder, despite its corrosion. It held 182,000 pounds more than the unsupported damaged beam.
Zaghi said the new method could effectively increase the service life of bridge components by 20-40 years. “If we can do it in here, construction crews can outside,” Zaghi said.
So why is traditional concrete so bad? Zaghi said its composition hasn’t been updated in a long time.
“Regular concrete was developed a thousand years ago,” Zaghi said. “It was not developed to be a super material. It was a material that was gradually improved and the stuff they use today is a lot better than what they used 50 years ago.”
The DOT took on sponsorship of the project looking for a repair method that could be done easily and quickly -- and potentially by state workers. State bridges are inspected every two years, but oftentimes, deterioration could get worse by the time it’s identified and contracted for repair, said RabihBarakat, the DOT’s principal engineer on the research team’s advisory committee.
Kevin McMullen, a PhD structural engineering student working on the project, said he’s interested in this study because of its practicality.
“The main problem that ordinary people who aren’t structural engineers have [with bridge repair] is traveling,” McMullen said. “And when highways are shut down for bridge repair or replacement, they really get frustrated being backed up in all that traffic, especially on I-84 lately.”
McMullen said that the concrete-based repair would only take a couple of hours to make, so bridges wouldn’t have to be totally shut down to be fixed.
In the project’s second phase, the team will set standards and guidelines for the concrete’s implementation in actual infrastructure projects. They’ll also conduct full-scale experimentation.
McMullen will focus his time in the next phase performing experiments on the the large steel beams you see on highway bridges. His tests, although only about two days in duration, will take months to prepare. The students are able to move the heavy bridge pieces around the lab using two cranes suspended from the ceiling, one of which is capable of supporting up to 25 tons.
They’ll have to increase the capacity of the hydraulic system to test loads on the steel beams up to one million pounds.
The team is also working with the DOT to select an actual bridge in Connecticut to test the repair method on.
There are several heavily-trafficked and structurally deficient bridges in Connecticut, including the Yankee Doodle Bridge on 1-95 in Norwalk or the the bridge over the Quinnipiac River on I-91, both of which average over 130,000 daily crossings and were built in the late 1950s.
The DOT has pursued other accelerated bridge solutions, like in 2014, when state workers replaced two I-84 bridges in Southington in just one weekend.
Bad bridges aren’t unique to Connecticut. Nationwide, one in nine of the bridges is rated as structurally deficient. But some reports have Connecticut’s bridge problem as one of the costliest in the nation to fix. It’s a regional problem too -- of the top five most costly highway bridge repair states, including Connecticut, four are in the Northeast and Mid-Atlantic.
Zaghi and his team didn’t invent this new super-strong concrete -- nor did they conceive of the original idea of using it to reinforce corroded steel. But Zaghi said researching and testing new innovations -- with the support of state government -- is crucial to the solving nationwide infrastructure conundrum.
“The question is,” Zaghi said, “Do we want to leave the same type of issues for our next generation?”
WNPR intern Karelyn Kuczenski contributed to this report.
