Smart paint

Scientists at Strathclyde University in Glasgow are developing a low-cost "smart paint" that uses nanotechnology to detect microscopic faults in civil engineering structures such as bridges and tunnels. Its low cost could be a selling point for cash-strapped governments.

Today, engineers often need to visually inspect bridges, tunnels, wind turbines and other large civil engineering structures for defects – a task that is both time-consuming and costly. In the not so distant future, smart paint technology could do the job faster and cheaper, and increase safety at the same time.

The idea is the brainchild of David McGahon, a doctoral student at Strathclyde University, who is working together with his advisor, Mohamed Saafi of the university's department of civil engineering.

Although their smart paint technique has not been fully described yet in any scientific journals, the scientists say they plan to submit a paper in the coming months.

The paint uses fly ash, a recycled waste product produced in the combustion of coal, which is mixed with carbon nanotubes capable of carrying an electrical current.

Nanotubes in paint

"Fly ash itself can carry a current but we have added networks of carbon nanotubes to make it even more conductive," Saafi told Deutsche Welle.

Fly ash is a construction material, often used in cement. As such, it gives the paint a cement-like property. Such durability, according to Saafi, is ideal for structures that must endure both high and low temperatures. The material, he adds, is also inexpensive.

When the carbon nantotubes bend, their conductivity changes. Electrodes interfaced with the paint detect the changes and transmit them to paired wireless transmitters capable of receiving and sending data. The result is a conductivity map that shows exactly where a crack appears in a structure.

For their research, the scientists are currently using batteries to power the wireless communication nodes but point to energy-harvesting possibilities.

"We can use, for instance, the vibrations of cars crossing bridges or trains passing through tunnels to harvest power," Saafi said.

Smart paint can be easily produced and applied, and monitoring requires no particular expertise, according to the researcher. Another big advantage, he added, is that, unlike current technologies restricted to monitoring specific areas of a structure at specific times, smart paint covers entire structures all the time.

High sensitivity required

The scientists in Glasgow have completed about 60 percent of their research, having studied, for instance, the percentage of carbon nanotubes necessary to make the solution cost-effective.

The team plans a field test either this summer or early next year. The interface with the wireless communications system and energy-harvesting capabilities will be a primary focus.

Some researchers, however, are skeptical of the ability of a surface sensor to fully receive data on cracks that may be deep inside the structure and question whether surface cracks may, in fact, disrupt the smart paint layer itself. Few are willing to comment on research in progress, especially since this new technique has yet to be subjected to peer review.

"Such sensibility is difficult to achieve in the real-life applications," wrote Azat Ibragimov, a doctoral student at the Institute for Microsensors, Actuators and Systems (IMSAS) at the University of Bremen, in an e-mail sent to Deutsche Welle. "The layer’s properties will be probably more dependent on other factors than the mechanical condition of the structure (temperature, humidity, layer’s own mechanical and chemical deterioration with time, et cetera)."

Author: John Blau
Editor: Cyrus Farivar