A new method to strengthen and repair deficient bridges with paper-thin material has been recognized.
A new method to strengthen and repair deficient bridges with paper-thin material has been recognized.
Wassim Ghannoum is an associate professor in the Departmentof Civil and Environmental Engineering at the University of Texas at San Antonio. He has spent the last 10 years perfecting a method to strengthen and repair deficient bridges and other concrete structures using carbon fiber reinforced polymer, CFRP. His research team recently published their work, which was funded by the Texas Department of Transportation, in the American Concrete Institute (ACI) Structural Journal. The paper was extremely well received as it was selected for ACI’s Wason Medal for Most Meritorious Paper, bestowed specifically for the “characterization of shear strengthening behavior of CFRP anchors and anchored strips”.
Ghannoum is not the first to experiment with using carbon fiber sheets in bridge repair. Nonetheless, the technique had been applied for many years but with mixed results. Ghannoum believes the biggest weakness with this process is the bond between the carbon and the concrete. When concrete is overstressed it crumbles and peels off the carbon fiber sheet with it. In his research though, instead of using sheets by themselves to cover cracks and fractures, Ghannoum is taking the carbon fiber and cutting it into strips called, anchors. These anchors made from strips of carbon fiber are folded over, coated with a special epoxy and inserted into holes about six inches deep drilled in a pattern around the damaged or weak area on a bridge. There’s a portion of the anchor that extends past the drilled hole. That portion is fanned out against the concrete and then covered with a specialized sheet of epoxied carbon fiber. This process has been working incredibly well with no known failures on bridges where applied.
“Carbon fiber is wonderful because if you anchor it properly, the way we demonstrate, you can increase the strength of bridges up to 50%,” Ghannoum said to UTSA Today. “A 50% increase of a massive bridge section, by applying something as thin as wall paper, is not a small thing.”
Ghannoum added that carbon fiber is ideal for this application because of its phenomenal strength-to-weight ratio. Another benefit of carbon fiber reinforced polymers are their ability to move with the underlying bridge when put under a strenuous load. Engineers call this deformation compatibility. A material that is too flexible would not pick up enough of the load under traffic, while a material that is too stiff would pick up too much of the load and break under pressure. Thus, carbon fiber has the right stiffness and strength to work superbly in this application.
Ghannoum’s discovery not only makes bridges stronger and safer, but also generates huge cost savings with everything from materials to labor and commerce. Because of its widespread use in manufacturing anything from musical instruments to high-performing vehicles, it’s readily available in large, high-quality quantities.
It’s also a time-saver. Bridge repair traditionally involves closing the structure and rerouting traffic. Workers arrive to remove the damaged portion before building forms to tie in rebar and pour concrete. It can take about 10 days for concrete to cure and gain strength. At this point, the bridge is tested under load before reopening. During this time, traffic is rerouted causing travel delays and disruption for homes and businesses along the detoured path. In comparison, Ghannoum’s process takes a fraction of the time with better results. “From a user’s perspective, you don’t close traffic because you can apply the carbon fiber anchor system in such a fast time,” Ghannoum said. “Instead of days, you can repair the bridge with a half day of work, so it’s a game-changer in that regard.” Despite its many advantages, the carbon fiber anchor system is still gaining understanding and acceptance throughout the engineering and construction industry. Source: UTSA TodaySources: TU Wien, NewAtlas