By Kevin Wilcox
Teams in Iowa and Italy collaborate to develop two different sensor technologies that will enable real time monitoring of large, complex structures.
April 1, 2014—Researchers in Ames, Iowa, and Perugia, Italy, are working collaboratively on separate nanocomposite materials technologies to measure the performance of large structures in real time and alert authorities to changes brought on by strain. The technology has the potential to provide alerts about such critical structural changes as cracks months or even years before they might have been discovered by visual inspections.
Cracks in critical steel and concrete structural members could be detected far earlier using nanotechnology-based, real-time sensors that are being developed and tested in Iowa and Italy. Wikimedia Commons/Achim Hering
At Iowa State University, a team led by Simon Laflamme, Ph.D., A.M.ASCE, an assistant professor of civil, construction, and environmental engineering, is developing a soft elastomeric capacitor (SEC) system—a surface covering that mimics human skin's sensing capability.
At the University of Perugia, a team led by assistant professor Filippo Ubertini, Ph.D., is developing a carbon nanotube, cement-based sensor (CNTCS). The carbon nanotubes are embedded in cement paste, either during casting or later by mortar application. Ubertini is currently focused on adding nanotubes to historical structures to monitor any changes following such extreme events as earthquakes.
"In both cases, they are similar in a sense that strain would provoke a change in geometry in the material," Laflamme explains. "For the CNTCS, it's a strain in the cement paste itself. Strain provokes a change in geometry, and a change in geometry provokes a change in [the] conductivity of the material." The system can be likened to a resistor; the electrical resistance of the cement paste changes based on the geometry of the strain.
"The SEC is similar, except a change in geometry on the skin will provoke a change in the capacitance," Laflamme says. "We have two different pieces of electronics here. One is a resistor, the other is a capacitor."
Both research teams are focusing on deploying their technology on a large scale. Laflamme notes that currently available technologies are either not economically feasible for large-scale applications or provide a data stream that is too complex to quickly analyze and distill into actionable information.
"We want to be able to deploy our technology on very large surfaces. Think of any civil infrastructure, or even mechanical systems," says Laflamme, who is currently working with both the wind turbine industry and the Iowa Department of Transportation (DOT) to develop specific applications of his SEC.
"With our technology, we are trying to develop sensing solutions around an application," Laflamme says. "An example of that is the project we have funded by the Iowa DOT. They would like to deploy the skin on key areas of a steel bridge. A skin would be able to detect and localize fatigue cracks. Fatigue cracks are very important to any DOT." The SEC would also be able to provide the location and size of any cracks detected.
"It really beats visual inspections," Laflamme notes, because visual inspections are conducted only a specific schedule, and fatigue cracks can appear any time—even soon after an inspection—and grow worse over time.
In the summer of 2013, researchers from the two schools met in Italy for a test of the two technologies utilizing a concrete beam. The tests revealed that both technological approaches work well in what Laflamme terms a basic test. Perhaps more importantly, the collaboration allowed each team to combine their strengths in different areas to advance the work of both.
"Our experience was quite complementary," Laflamme says. "We were both able to advance our solutions to the next level by discussing and giving feedback on what is happening with each other's technologies. It was phenomenal. When you do these exchanges, you have the opportunity to really focus for the time you are there. We were there for a full week of brainstorming, discussions, tests, and data analysis."
The team recently published the paper"Novel Nanocomposite Technologies for Dynamic Monitoring of Structures: a Comparison between Cement-Based Embeddable and Soft Elastomeric Surface Sensors" in the journal Smart Materials and Structures. Other papers are being developed, and the two teams plan to continue their collaboration. The next steps in the development of the technologies are to test for the ability to localize damages, develop a large-scale test project, and formulate a method to quantify the cost savings that the technology might offer to infrastructure stakeholders.
"How do your prove that a sensing technology will make you save money by increasing the lifecycle of the structure? To me it's intuitive. [But] if someone asks for data, we don't have much," Laflamme says. "So there is some work to be done in demonstrating that there is an important rate of return on investment for sensing solutions."