If Roads Could Talk: Sensors Communicate Inner Workings of Infrastructure

What if infrastructure could talk? What if our roads and bridges could sense areas of internal weakness or compromised integrity and share that information with civil engineers? That information might not just help maintain transportation infrastructure, but could lead to better, more cost effective decision-making when the time comes to set priorities and allocate limited resources.

Nizar Lajnef, an associate professor of civil and environmental engineering at Michigan State University, is working to develop sensors that have the potential to give infrastructure that ability. In partnership with the U.S. Department of Transportation and the Federal Highway Administration, Lajnef is creating smart sensors that diagnose damage and mechanical failure in roads and bridges. It's a project that Lajnef has been working on since his days as a doctoral student.

Challenges

Developing technology that is intended to be imbedded in pavement presents some unique challenges. For example, the sensors Lajnef and his team are working on are self-powered. They have no batteries and rely on energy scavenged from the vibration and strain of their environment. This works because the sensors require very little energy—the prototype used less than 800 nanowatts of power.

The sensors must also be able to perform autonomous computation and store data in such a way that it is not lost with loss of power (non-volatile memory).

"The sensors operate in two modes," Lajnef explained. "The first mode, which is the data collection and recording mode, is completely self-powered using piezoelectric transducers. The loading events from traffic induced on the bridge or pavement generate enough power for the sensors to wake up, sense the event (strain and acceleration), and record the event on the sensor itself in a non-volatile memory. The data are kept on the sensors."

The second mode is when the data are transferred to operators. The data, which have been saved on the sensors, are transferred wirelessly when the sensors are scanned with a reader.

"When we designed the communication part, we made sure to use protocols that are available and approved by the Federal Communications Commission," Lajnef said. So the sensors can be read by any wireless device, including smartphones. Their portable nature means the readers might be handheld or kept on a vehicle.

Potential Economic Impacts and More

"The key word when it comes to saving money is preservation," Lajnef said. He points to the common occurrence of cracks in pavement as an example of how the technology can save money. "Cracks that start at the bottom of the pavement are currently detected only when they show up at the surface, so maintenance is costly at that time," he explained. "Now imagine you can detect the damage as soon as it starts at the bottom. Then you can plan the appropriate preservation intervention at the appropriate time and, thus, increase the lifetime of the structure and save money on costly maintenance."

As seen with the collapse of the I-35W Mississippi River bridge in Minnesota in 2007, infrastructure maintenance is more than just an economic concern. It has the potential to save lives. "What the sensors are able to achieve," Lajnef said, "is to detect damage before it is too critical and requires immediate intervention. That way you can plan for it ahead of time."

Infrastructure maintenance is just one application of this technology. To explore the ways the sensors can be developed for other uses, and the commercial potential that it creates, Lajnef partnered with former MSU professor Shantanu Chakrabartty to form Piezonix (www.piezonix.com). The Michigan-based company has received funding from the National Science Foundation to explore the use of the sensors for the monitoring of biomechanical implants and trauma fixation devices.

The project is funded with about $2.2 million from the U.S. Department of Transportation and the Federal Highway Administration. Early prototypes of the sensors have been tested at the Turner Fairbanks Highway Research Facility, a U.S. Federal Highway Administration facility near Washington, D.C.

Next year, testing moves closer to home when Lajnef will begin working closely with the Michigan Department of Transportation on testing sites not far from East Lansing.