Iowa State University researchers pushed a 71-foot-long bridge beam as far as they could to find out how much pressure it would take before breaking. They set up four hydraulic devices to exert pressure on the beam, which was made of ultra-high performance concrete.

 

After about two hours and nearly 600,000 pounds of force—which translates to more than the weight of seven semi trucks—the beam finally broke.

 

The capacity test, funded by the Federal Highway Administration and the Iowa Highway Research Board, was part of a $450,000 project to study the innovative concrete, made of sand, cement, water, and small steel fibers. Ultra-high performance concrete does not contain the coarse aggregate found in standard concrete, making it denser and stronger.

 

Even though it’s more expensive, the new product is expected to last much longer and can hold twice the load of a similar beam made of standard concrete.

 

County engineers and officials from southeast Iowa were on hand for the test, which held special interest for them because a similar beam will be used this summer to construct a bridge over Little Soap Creek in Wapello County. It’s the first time, according to Brent Phares, associate director of Iowa State’s Bridge Engineering Center, that ultra-high performance concrete will be used for a bridge in the United States.

 

“It’s a new type of concrete,” Phares says, “and there were some questions on design. We had some specifications, but they were very conservative and there were lots of unknowns.”

 

Phares feels he better understands the new concrete after the test and is confident in its usability and safety. “We actually exceeded all of the specifications that are out there,” he says. “We’re very happy.”

 

Once the bridge is constructed, Phares adds, his group will monitor its performance over a two-year period.

 

Brian Moore, Wapello County engineer and Iowa State University graduate (CE’86), was impressed by what he saw. Moore says Iowa State approached him looking for a possible location to construct a bridge using the new concrete. He had a location, and since the county would be eligible to receive some federal money to help pay for the project, he was glad to get involved. “It was a win-win for the county and the university,” Moore says. “In the end, research on the use of this material is advanced and we get a bridge for about half the price.”

 

Moore was anxious to see the beam break and curious about how much force it could withstand.

 

After the test, Brian Degen, a civil engineering graduate student from Urbandale, Iowa, who has been working on the project from the beginning, was confident that Moore would be happy with the results. “We need to look at some of the numbers,” Degen says, “but the main thing is the beam is strong enough for the bridge that we’re going to put in Wapello County.”

 

Even state Department of Transportation officials were happy with the test results.

 

“I’m impressed with what we saw,” says the DOT’s Dean Bierwagen. “I think we’ll have a solid bridge when it’s all done.”