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April 10, 2019

CERL designs, 3D-prints America’s first reinforced-concrete bridge



As reported in The News-Gazette, a Champaign lab has designed and 3D-printed the first reinforced-concrete bridge in the country.

The U.S. Army Corps of Engineers’ Construction Engineering Research Laboratory was testing the 3-foot-wide foot bridge last week, hoping it would be able to withstand the 15,000 pounds it was designed for.

It blew that away, not cracking under a hydraulic actuator until it was under the equivalent of nearly 45,000 pounds.

“It’s really exceeding the designed strength by quite a bit,” said Mike Case, the program manager. “So it’s really proving it is a valid way to construct structural members, like bridges.”

CERL has been 3D-printing with concrete since 2015, starting with a simple fighting position and a guard shack.

In 2017, it 3D-printed a barracks with straight walls, and last year, it printed another barracks with angled walls that is twice as strong with only 10 to 15 percent more concrete.

The 3D printer works more or less like the those used at schools and makerspaces, but instead of printing layers of plastic, it prints layers of concrete.

“It’s fairly similar. There is a huge difference in scale, so you get all the problems associated with scale,” said Megan Kreiger, the printing lead on the project. “But as far as the fundamentals of the technology, it’s essentially the same, except for instead of using a plastic filament, you’re now using a concrete pump with a concrete hose and you’re feeding concrete through.”

Using concrete, which is heavier and doesn’t solidify as quickly as plastic, does limit them on the shapes they can build.

“So with regular 3D printing, you can get all kinds of crazy 3D geometries,” Kreiger said. “With concrete, you can still get a little bit of variation in geometry, but it’s still wet concrete as you print, so there’s more limitations in what you can do.”

Each layer is about an inch thick and cures after a few minutes.

Keep reading in The News-Gazette


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