Electrical Resistance Of "Smart" Concrete Changes Under Stress

Truck-weighing stations on highways could become a thing of the past as a result of a new application for "smart concrete" developed by researchers from the University at Buffalo (UB; Buffalo, NY; 716-645-2626). By reinforcing the concrete with carbon fibers, the research team created a material with an electrical resistance that changes under stress.

How It Works
Applications


How It Works (Back to Top)
When concrete is reinforced with a small amount of carbon fiber (between 0.2% and 0.5% of volume), its electrical resistance changes in response to strain or stress. "Smart" concrete made with this formula was developed and patented by Deborah Chung, UB Niagara Mohawk Chair of Materials Research and professor of mechanical and aerospace engineering. Zeng-Qiang Shi, a graduate student in the UB Department of Mechanical and Aerospace Engineering, also participated in the research.

"Concrete modified with carbon fibers turns out to be a very sensitive detector of strain," Chung says. "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."

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 Chung's smart concrete material. The researchers controlled both the speed of rotation and 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. By calibrating the concrete prior to testing, the researchers were able to determine the relationship between resistance and weight.

According to Chung, the electrical resistance of smart concrete decreases as the stress increases up to 1 Mpa. This relationship is independent of speed, up to 55 miles per hour.

Applications (Back to Top)
"A highway made with smart concrete would be able to tell where each vehicle was, and what its weight and speed were," Chung says. "As a result, vehicles could be weighed while traveling normally on the highway."

Chung said that the extra cost of adding short carbon fibers to concrete would increase the materials cost of concrete by about 30%. This expense is still significantly cheaper than attaching or embedding sensors into roads, a method already in use by some highway authorities.

Other applications for smart concrete include using it to sense real-time vibrations of bridges or other highway structures. It could also be used in buildings to dampen vibrations or reduce earthquake damage.

The research was funded by the National Science Foundation and Sensor Plus Inc. (Amherst, NY). A paper on the research authored by Chung and Shi will be published in the May 1999 issue of Cement and Concrete Research.

For more information, call the University at Buffalo at 716-645-2626.

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