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Hear That? Listening for Bridge Defects

A civil engineer has designed an acoustic approach to detect defects in concrete bridge decks.

The system represents an alternative to the conventional method of of dragging chains along a bridge service to identify delamination, a gradual separation of concrete layers that can subtly compromise the structural integrity of a bridge.

"When we find this delamination, we should fix it," says JinyingZhu, assistant professor of civil engineering at the University of Nebraska-Lincoln. "Otherwise, in the winter, salt (or) water will come in and cause further corrosion."

Zhu's system consists of a push-cart that drags multiple strings of brass balls along the concrete. The balls produce different acoustic frequencies when striking delaminated versus pristine concrete. Small, low-cost microphones attached to the cart record the sound and send it to a laptop that collects and processes the signals. A specialized GPS unit tracks the cart's location down to the centimeter.

By correlating acoustic signals with the cart's position, the system's software can generate a color-coded map that illustrates the location and dimensions of a bridge's defects. Deep-blue segments indicate pristine concrete, with dark red representing the most severe delaminations.

With support from the Nebraska Department of Transportation, Zhu and her colleagues have recently demonstrated that the system could assess bridges at least several times faster than existing methods.

This article first appeared on

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