Calling in the reinforcements: epoxy with moxie

12/20/2016

At any point in time, a bridge can have hundreds of cracks in its concrete beams. These are expected and don’t pose a risk to the bridge’s structural integrity or public safety. However, if there is significant damage due to environmental degradation or external forces, safety becomes a major concern and repairs become necessary.

Shutting down a bridge for repair can be extremely expensive and time consuming, and disruptive and frustrating for the public. It’s also labor-intensive and usually involves heavy equipment.

Researchers at Penn State are now gaining more insight into a more efficient and effective reinforcement solution that is gaining greater acceptance for strengthening, rehabilitating, retrofitting, and repairing reinforced concrete structures in civil infrastructure applications such as bridges and buildings—bonded fiber-reinforced polymer (FRP) reinforcement systems.

For more than 20 years, Charles E. Bakis, Distinguished Professor of Engineering Science and Mechanics, along with Thomas E. Boothby, professor of architectural engineering, has been investigating the long-term performance of bonded FRP systems that incorporate highly oriented carbon fibers and epoxy polymers that, when bonded to concrete, provide structural reinforcement eight times greater than steel reinforcements on a unit weight basis.

Dry carbon fibers have exceptional strength-to-weight and stiffness-to-weight ratio, making them extraordinarily strong; however, they lack the ability to adhere to each other. Epoxies, on the other hand, do not have great strength but can provide a matrix of “glue” to hold the carbon fibers together and bond them to concrete.

To conduct the research, Bakis first applies these materials in layers to plain concrete beams to form a composite material—applying an epoxy primer that soaks into the concrete’s pores, an epoxy “putty” that fills in holes and levels the surface, and aligned carbon fiber sheets saturated with a third type of epoxy. All of this is done in much the same way paint is applied. He then bends the beams to form cracks in the concrete and to get the load into the composite, where it acts as the only tensile reinforcement for the beam.

By placing the entire specimen under sustained bending load and various environmental conditions for several years, he is able to evaluate how the degree of cure of the epoxies and the bond strength between the FRP and concrete vary over time.

“Despite the increased popularity of bonded FRP reinforcement systems, data on their long-term bond and tensile behavior has been scarce,” said Bakis. “What we’ve found after seven years of loading under aggressive indoor and outdoor conditions is that the bond strength holds up amazingly well, and the composite materials prevented cracks from growing. There was also very little change in bond behavior in either environment.”

With rapid installation time, carbon FRP reinforcement systems can now provide bridge and building owners a quick, low-labor, cost-effective, and easy method for repairing and rehabbing degraded or damaged bridges and buildings. They also allow the structures to recover their original strength and margin of safety they lost, and even handle higher loads than originally designed for.

Bakis said bonded FRP reinforcement systems won’t ever replace steel rebars in concrete beams as the primary source of tension support. But, if there is a need to quickly and safely strengthen a bridge or retrofit and change the use of a building to handle greater loads, they are the preferred method.

 

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MEDIA CONTACT:

Chris Spallino

cjs53@psu.edu

Concrete beam with applied FRP system

A concrete beam showing an applied bonded FRP system.

Concrete beam under sustained load

Coated concrete beams under sustained load.

“What we’ve found after seven years of loading under aggressive indoor and outdoor conditions is that the bond strength holds up amazingly well, and the composite materials prevented cracks from growing."

 
 

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The Penn State Department of Engineering Science and Mechanics (ESM) is an internationally distinguished department that is recognized for its globally competitive excellence in engineering and scientific accomplishments, research, and educational leadership.

Our Engineering Science program is the official undergraduate honors program of the College of Engineering, attracting the University’s brightest engineering students. We also offer graduate degrees in ESM, engineering mechanics, engineering at the nano-scale, and an integrated undergraduate/graduate program.

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The Pennsylvania State University

University Park, PA 16802

Phone: 814-865-4523