Hi-Tech 'Skin' Senses Bridge Damage

Aug. 10, 2007 — Just like human skin can feel cuts, bumps and bruises, a new paint-on coating for bridges and other structures can sense damaging corrosion, cracking and strain.

The layer — which can cover a large area but measures thinner than a human hair — could allow inspectors to closely monitor the health of a bridge or building without examining it physically.

If the technology had been in place on the I-35 bridge in Minneapolis, it might have sensed unusual stress or strain and alerted engineers before the bridge's devastating collapse last week.

"The method doesn't require any human intervention. Once you have it there, you have a skin that will react to its environment when it's stimulated," said Jerome Lynch, assistant professor in the University of Michigan.

The hi-tech skin is made from layers of polymer with networks of tiny carbon nanotubes. These molecules look like long strings of thread and can conduct electrons at ballistic speeds.

Lynch, along with associate professor of chemical engineering Nick Kotov and their team, designed the layers to have different sensing properties. One is sensitive to the metal's acidity, which changes when it starts to rust. Another layer is sensitive to cracks or strain.

As corrosion or cracks occur, the behavior of the electrons passing through the layer changes. Lynch likened it to speaking in an empty room: Without furniture, your voice has a bit of an echo. But adding furniture changes the sound of your voice in a noticeable way.

To pick up the changes that occur in the event of cracks and corrosion, the scientists use wireless electrodes, or nodes, placed along the bridge.