You wouldn’t expect to find a bridge with state-of-the-art GFRP decking on a two-lane, rural road. But there’s one on Elizabeth Church Road in Morgan County, Tenn. Constructed through the efforts of a public-private partnership, the structure is intended to demonstrate the benefits of composite materials for bridge.
There’s a real need for this solution. The American Society of Civil Engineers estimates that 7.5% of the 617,000-plus bridges in the U.S. are structurally deficient and need repair. FRP composites offer a proven, low-cost, low-maintenance option.
Composites have been used for bridge deck projects for more than 20 years and have exceeded all of the performance and safety standards set by the American Association of State Highway and Transportation Officials (AASHTO), according to John Unser, vice president of program and project management at Composite Applications Group (CAG) and a consultant technology impact manager with IACMI – The Composites Institute®. The problem is that many highway directors and managers, especially those from smaller jurisdictions, still aren’t familiar with the technology.
The public and private entities that built the Morgan County bridge want to change that. Composite Applications Group, headquartered in Tennessee, and Structural Composites Inc., based in Florida, had already been exploring possible infrastructure opportunities with IACMI when the coronavirus pandemic hit. When normal business slowed and funding through the Paycheck Protection Program became available, the time seemed right to pursue a demonstration project. Because of its experience working with industry and government, IACMI took the lead.
Jeff McCay, CEO of CAG, discussed the composite bridge technology with Brian McKinney, president of McKinney Excavating in Tennessee. McKinney introduced McCay to Joe Miller, Morgan County’s highway superintendent, who was very interested in testing a composite bridge deck on one of the county’s distressed bridges. “One of the things that we think is pretty critical, especially in rural areas, is finding a champion,” McCay notes.
The group chose a bridge that is 25 feet wide and just 16 feet long. That short length was desirable since the Tennessee Department of Transportation does not have to sign off on bridges less than 20 feet long. (Concerns about risk mitigation may hamper state DOTs from approving new technologies.)
The bridge partnership then expanded to include researchers from the University of Tennessee’s Fibers and Composites Manufacturing Facility. They put together a system of fiber optic sensors, which was embedded in the composite decking during manufacturing, plus a module that enables the university researchers to monitor the structure over time. The sensors, developed by Luna Innovations Inc., will measure strain from mechanical loading and thermal/hygroscopic (humidity) loading from thousands of points.
“The lack of solid performance data has been one of the major roadblocks to widespread use of composite bridges,” says Dayakar Penumadu, the Fred N. Peebles Professor in the University of Tennessee Tickle College of Engineering and characterization fellow in the materials and processing group for IACMI. UT researchers and students will continue to monitor the bridge’s performance remotely through cloud computing. (The public can view monitoring data at compositebridge.org.)
“Although it’s a small span, it’s designed as a highway bridge deck, so all of the sensing data that we will be gathering is similar to what we would be seeing on a highway bridge. It’s a very low-risk way to gather real-time data that will give DOTs some confidence in the technology,” McCay says.
The team plans to develop a comprehensive case study comparing the total costs of a typical concrete bridge and one using an FRP bridge deck. “We will share the case study framework and results with federal, state and local officials, transportation departments and the civil engineering community so FRP composites will be more of a ‘known’ to them,” says Unser.