Researchers at North Carolina State University (Raleigh, North Carolina) and the University of Eastern Finland (Joensuu, Finland) are working together on the development and commercialization of a new electrical imaging method to track the infiltration of water in concrete structures.
The new technique could enable engineers to better identify potential issues before they become major problems, according to Mohammad Pour-Ghaz, an assistant professor of civil, construction and environmental engineering at North Carolina State University and lead investigator on the project.
Pour-Ghaz explains that water can contribute to the degradation of concrete by itself, or it may carry other chemicals—such as road salt used on bridges—to expedite the corrosion of both concrete and the underlying steel reinforcement structure.
“The technology allows us to identify and track water movement in concrete using a small current of electricity that is faster, safer, and less expensive than existing technologies—and is also more accurate when monitoring large samples, such as structures,” Pour-Ghaz says.
“The technology can not only determine where and how water is infiltrating concrete, but how fast it is moving, how much water there is, and how existing cracks or damage are influencing the movement of the water,” he adds.
Limitations of Previous Technologies
Prior technologies used to assess water in concrete generally relied on x-rays or neutron radiation, according to the researchers, who say that both have significant limitations.
For instance, x-rays offer only limited penetration into concrete, making it difficult to use with large samples or on structures. Neutron radiation technologies offer more accurate readings, but they also have limited penetration, are expensive, and pose health and safety risks, Pour-Ghaz explains.
“Our electrical imaging approach is something you could use in the field to examine buildings or bridges, which would be difficult or impossible to do with previous technologies,” he says.
Previously, it had been shown that electrical resistance tomography could be used to monitor moisture flow in undamaged cement-based materials, says Danny Smyl, a Ph.D. student at North Carolina State who helped conduct the research and served as lead author on three published technical papers regarding the technology.1-3
But through the new technique, the researchers found that tomography can also be used for imaging three-dimensional (3-D) unsaturated moisture flow in cement-based materials that contain discrete cracks, Smyl says.
How the Technology Works
To conduct the electrical imaging test, researchers apply electrodes around the perimeter of a structure. A computer program is then used to direct a small current between two of the electrodes at a time, cycling through numerous possible electrode combinations.
Each time the current passes between two electrodes, data are monitored and recorded regarding the electrical potential at all of the structure’s electrodes. The researchers then use their own customized software to compute the changes in conductivity and produce a 3-D image of the water in the concrete structure.
“By rapidly repeating this process—and we can do it even more than once per second—we can also capture the rate, and therefore the volume, of the water flow,” Pour-Ghaz says.
In essence, the imaging uses electrical measurements from the concrete structure’s surface to reconstruct the electrical conductivity distribution inside the structure.
“Our results indicate that [the technology] is a viable method of visualizing 3-D unsaturated moisture flow in cement-based materials with discrete cracks,” Smyl says.
What Comes Next
The researchers have already created and tested a prototype of the system in a lab environment. According to Pour-Ghaz, the prototype successfully captured images of water flow in concrete samples that were too large to be analyzed using x-rays or neutron radiation.
Using the prototype, the researchers say they were also able to successfully monitor water flow through cracks in concrete, which is more difficult and time consuming when using older technologies.
“Our electrical imaging technology is ready to be packaged and commercialized for laboratory use, and we’d also be willing to work with the private sector to scale this up for use as an on-site tool to assess the integrity of structures,” Pour-Ghaz says.
For now, the researchers say they are already satisfied by making significant progress to further enhance public safety.
“When we think about construction—from bridges and skyscrapers to nuclear plants and dams—they all rely on concrete,” Pour-Ghaz says.
Contact Mohammad Pour-Ghaz, North Carolina State University—e-mail: mpourghaz@ncsu.edu.
References
1 D. Smyl, R. Rashetnia, M. Pour-Chaz, A. Seppänen, “Can Electrical Resistance Tomography be used for imaging unsaturated moisture flow in cement-based materials with discrete cracks?” Cement and Concrete Research 91, 1 (2017): pp. 61-72.
2 D. Smyl, M. Hallaji, M. Pour-Chaz, A. Seppänen, “Quantitative electrical imaging of three-dimensional moisture flow in cement-based materials,” Int. J. Heat Mass Transfer 103, 12 (2016): pp. 1,348-1,358.
3 D. Smyl, M. Hallaji, M. Pour-Chaz, A. Seppänen, “Three-Dimensional Electrical Impedance Tomography to Monitor Unsaturated Moisture Ingress in Cement-Based Materials,” Transport in Porous Media 115, 1 (2016): pp. 101-124.
Bibliography
Shipman, M. “New Tech Uses Electricity to Track Water, ID Potential Problems in Concrete.” NC State News. November 1, 2016. https://news.ncsu.edu/2016/11/new-tech-uses-electricity-to-track-water-id-potential-problems-in-concrete/. Dec. 12, 2016.