May 20, 1999 BUFFALO, N.Y. -- Truck-weighing stations on highways could become a thing of the past as a result of a new application for "smart concrete" developed by University at Buffalo engineers.
A paper on the research authored by Deborah D.L. Chung, Ph.D., UB Niagara Mohawk Chair of Materials Research and professor of mechanical and aerospace engineering, and Zeng-Qiang Shi, a graduate student in the UB Department of Mechanical and Aerospace Engineering, is published this month in Cement and Concrete Research.
"A highway made with smart concrete would be able to tell where each vehicle was, and what its weight and speed were," said Chung. "As a result, vehicles could be weighed while traveling normally on the highway."
Developed and patented by Chung, smart concrete is concrete that has been reinforced with short carbon fibers. She previously demonstrated that the electrical resistance of concrete that has been modified with a very small amount of fibers (between 0.2 and 0.5 percent of volume) changes in response to strain or stress. The concrete acts as a sensor because the carbon fibers are much more electrically conductive than the concrete mix.
"Concrete modified with carbon fibers turns out to be a very sensitive detector of strain," said Chung. "Strain, which relates to stress, is detected through measurement of the electrical resistance. As the concrete is deformed or stressed, the contact between the fiber and cement matrix is affected, thereby affecting the volume electrical resistivity of the concrete."
By calibrating the smart concrete prior to the testing, the researchers were able to determine the relationship between resistance and weight.
In their lab, the researchers duplicated the weight and motion of a truck traveling on a highway by rotating a car tire between the cylindrical surfaces of two concrete rollers, one of which was made of smart concrete. The researchers were able to control the speed of rotation, as well as the load on the tire.
Four electrical contacts attached to the smart-concrete roller measured changes in electrical resistance of the concrete near its surface as the wheel rolled on it.
According to Chung, the electrical resistance of smart concrete decreases reversibly with increasing stress up to 1 MPa (megaPascals, a unit of stress equal to 145 lb per square inch) and is independent of speed up to 55 miles per hour.
Other applications for smart concrete include using it to sense real-time vibrations of bridges or other highway structures or buildings for use in dampening vibrations, or for earthquake-mitigation.
Chung said that the extra cost of adding short carbon fibers to concrete would increase the materials cost of concrete by about 30 percent, still significantly cheaper than attaching or embedding sensors into roads, a method already in use by some highway authorities.
The research was funded by the National Science Foundation and Sensor Plus, Inc.
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