‘Sensing skin’ could monitor the health of concrete infrastructure continually and inexpensively

June 29, 2011

By Denise Brehm
Civil & Environmental Engineering

In 2009, the American Society of Civil Engineers (ASCE) assigned a grade of “D” to the overall quality of infrastructure in the United States, saying that ongoing evaluation and maintenance of structures was necessary to improve that grade. Since then, federal stimulus funds have made it possible for communities to repair some infrastructure, but high-tech, affordable methods for continual monitoring remain in their infancy. Instead, most evaluation of bridges, dams, schools and other structures is still done by visual inspection, which is slow, expensive, cumbersome and in some cases, dangerous.

Civil engineers at MIT, working with physicists at the University of Potsdam in Germany, recently proposed a new method for continual electronic monitoring of structures. In papers appearing in Structural Control Health Monitoring (December 2010) and the Journal of Materials Chemistry (April 2011), the researchers describe a flexible fabric with electrical properties that could adhere to areas prone to cracking — such as the undersides of bridges — and detect cracks almost immediately when they occur.

Installing this “sensing skin” would be as simple as unrolling it and gluing it to the surface of a structure. The rectangular patches on the skin that detect changes in its electrical charge could be tailored in a geometric design appropriate for the type of crack likeliest to form in a particular part of a structure: for example, diagonal square patches to detect cracks caused by shear, or horizontal patches to detect the cracks caused by a sagging horizontal beam.

The formation of a crack would cause a tiny movement in the concrete under the patch, changing the capacitance, or stored energy, of the sensing skin. Once a day, a computer system attached to the sensing skin would send a current to measure the capacitance of each patch and detect any difference among neighboring patches. In t