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Professors Win Grant to Study Concrete Strengthening and Repair
Toby Weber

When concrete on a bridge or building deteriorates, cracks or is weakened, the structure doesn’t need to be torn down and replaced. Instead, it can be repaired and strengthened with advanced materials such as carbon fiber reinforced polymers (CFRP) that are more than five-times stronger than steel when placed under tension. While cheaper than, say, constructing a whole new bridge, a single such repair can easily cost hundreds of dollars once equipment handling, materials, labor, and other expenses are added up. Multiply that by the hundreds or even thousands of repairs that a single city or state may perform each year, and even these cheap fixes can put a dent in any budget.

That’s why repairing concrete in our deteriorated and ageing infrastructure remain a challenge and a topic of continuous research. “We understand how the concrete behaves and how the carbon fiber material by itself behaves. But when you combine the two of them, nobody has a good idea about how they interact, glue to each other, and form a composite system,” said Ashraf Ayoub, associate professor in the UH Cullen College of Engineering’s Department of Civil and Environmental Engineering.

This interaction between concrete and CFRP sheets is the subject of a research project being conducted by Ayoub and Civil and Environmental Engineering Chairman Abdeldjelil “DJ” Belarbi that recently won a $300,000 grant from the National Science Foundation.

This award comes on the heels of a multi-year study funded by the National Cooperative Highway Research Program (NCHRP) of the National Academies. Under this project, principal investigator Belarbi, Ayoub and researchers from three other universities developed design specifications and guidelines for bridge and highway engineers to use when deploying CFRP sheets on concrete girders to better withstand shear loading. As part of their study, they investigated more than twenty existing models of the interaction of concrete and CFRP sheets. “The results of this NSF project would have been ideal if they were available prior to the NCHRP project,” Belarbi said.

With the latest funding, the researchers will place CFRP sheets on concrete elements and then subject them to different loads and stresses.

The University of Houston is one of the only places in the world where such research can take place, Ayoub said. That’s because UH is home to the Universal Element Tester (UET). Housed in the Thomas T.C. Hsu Structural Research Laboratory, this nearly 40-ton machine can subject concrete panels to various loads, including compression, tension, shear, bending, torsion and their combinations. It is one of only two machines in the world with this capability. 

“If the UET were not here, it would have been very hard for us to do this research,” Ayoub said. “This is work that probably should have been done 10-15 years ago but nobody did it because nobody had the right testing equipment.”

To mirror how concrete can be repaired in the field, when performing these experiments Ayoub and his research group will adjust multiple parameters, including the angle at which the sheet is placed, the sheet thickness, the adhesive used to attach it to concrete, and the concrete mixture itself.

After subjecting the repaired and strengthened concrete panels to loads applied by the UET, Ayoub and Belarbi will analyze the crack patterns to uncover the rules for how CFRP/concrete system behaves.

This information can then be used to determine the best way to repair individual cracks, as well as to extrapolate how an entire concrete structure will behave after it is repaired. “Once you understand the behavior you can integrate that to understand how the larger girders and other structures behave,” Ayoub said. “Eventually this should allow for more sound structural design and better repair applications and methodologies.”

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