A European-American team has developed a new technique for tracking water in concrete structures, allowing engineers to identify potential issues before they become big problems.
The researchers from North Carolina State University and the University of Eastern Finland say, tracking concrete degradation is essential to public safety, and the culprit behind concrete degradation is water. Water contributes to the degradation by itself, or it can carry other chemicals, such as the road salt used on bridges, that can expedite corrosion of both concrete and its underlying steel reinforcement structure.
“When we think about construction, from bridges and skyscrapers to nuclear plants and dams, they all rely on concrete,” said lead investigator on the project Professor Mohammad Pour-Ghaz from the NCSU College of Engineering.
“We have developed a technology that 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 said the technology can not only determine where and whether 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.
Previous technologies for assessing this relied on X-rays or neutron radiation, but both have significant limitations, including limited penetration into the concrete, making them difficult to use with large samples or on structures.
“Our electrical imaging approach is something that you could use in the field to examine buildings or bridges, which would be difficult or impossible to do with previous technologies,” he said.
For their electrical imaging technique, researchers apply electrodes around the perimeter of a structure. A computer program then runs a small current between two of the electrodes at a time, cycling through a number of possible electrode combinations.
Every time the current runs between two electrodes, a computer monitors and records the electrical potential at all of the electrodes on the structure. The researchers then use their own customized software to compute the changes in conductivity and produce a three-dimensional image of the water in the concrete.
“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 said.
The researchers have already created and tested a prototype of the system in a lab, accurately capturing images of water flow in concrete samples that are too large to be analyzed using X-rays or neutron radiation. The researchers have also been able to monitor water flow through cracks in concrete, which is more difficult and time-consuming when older technologies are used.
[A cracked sample tested in the research, with a computer image in the background showing the flow of water in crack. Photo: Julie Williams Dixon/NCSU]