It broke with a loud pop.
And then Iowa State University researchers gathered around to examine the long diagonal crack along one end of a 71-foot bridge beam made of ultra-high performance concrete. The capacity test was part of a $450,000 project to study the innovative concrete. The project was funded by the Federal Highway Administration and the Iowa Highway Research Board.
The researchers spent Thursday morning applying more and more hydraulic pressure to the top of the beam. They wanted to see how much it could take before breaking. And it took a lot: 595,000 pounds of load. That's more than the weight of seven semi trucks.
Brian Degen, a graduate student in civil engineering, said researchers had predicted the beam would break under 640,000 pounds of load.
It couldn't hold that much. But Brent Phares, the associate director of Iowa State's Bridge Engineering Center, said a similar beam isn't going to have any problems holding up 100th Avenue over Little Soap Creek in southeast Iowa's Wapello County. When that bridge is built this summer, it will be the first time engineers will use ultra-high performance concrete in an American bridge.
Ultra-high performance concrete is made from sand, cement, water and small steel fibers. It does not contain the coarse aggregate found in standard concrete. Because the ultra-high performance concrete is engineered to include finer materials and steel fibers, it's denser and stronger than standard concrete.
Phares estimated a beam of ultra-high performance concrete can hold twice the load of a similar beam made of standard concrete.
Did the researchers learn anything else from their cracked beam?
Yes, said Degen, "This bridge is going to be strong."