Composite bridge in US' city demonstrates alternative for old bridges

April 14, 2021 - United States Of America

A new high-tech composite bridge in north central Tennessee is being seen as demonstrating the benefits of composite materials for rural bridge work. The bridge has been constructed under a partnership led by the Advanced Composites Manufacturing Innovation, or IACMI—The Composites Institute. It replaced a damaged, decades-old concrete crossing.

There are thousands of rural, low-volume bridges across the state and the country which have been rated structurally deficient and outdated. According to the American Society of Civil Engineers, about 8 per cent of the more than 617,000 bridges in the US are structurally deficient and need repair.

The new bridge is equipped with a fibre-reinforced polymer (FRP) composite material bridge deck embedded with fibre optic sensors. FRP composites offer a low-cost, low-maintenance option. The new structure in rural Tennessee demonstrates the benefits of composite materials for rural bridge work.

"This composite bridge has already made a positive impact on Morgan County," said Morgan County highway superintendent Joe Miller, and added county officials were looking for a low-maintenance bridge that could be installed fast and at a lower cost than traditional methods. "We have numerous bridges within the county and hundreds across the state that are in need of repair and could benefit from this technology."

For Morgan County, the lightweight, easy-to-install bridge comes at no cost, courtesy of the composites industry. Working together under the umbrella of the Institute for Advanced Composites Manufacturing Innovation, or IACMI—The Composites Institute, almost a dozen private companies led by Tennessee-based Composite Applications Group (CAG) partnered with industry organisations and university researchers to make the composite bridge a reality.

Developed by Structural Composites (SCI), the 16-feet-long and 25-feet-wide bridge deck is engineered for high-strength and is 90 per cent lighter than concrete. It has two 8-by-25-foot corrosion resistant FRP deck panels that were fabricated off-site in a controlled environment.

Because the completed bridge sections were so lightweight, they could be transported to the bridge site and installed in one day using a forklift, reducing installation time and energy costs by requiring less construction equipment for on-site preparation.

IACMI technology manager John Unser, who is also vice president of programme and project management for CAG, said composites have been used for bridge deck applications for more than 20 years and have exceeded all performance and safety standards set by the American Association of State Highway and Transportation Officials (AASHTO). But when it comes to composite bridge decking, he said, many transportation departments across the country, especially those from smaller jurisdictions, are not familiar with the technology.

IACMI and its industry partners are developing a comprehensive case study based on the Morgan County bridge project, including comparing total costs of a typical concrete bridge and one using an FRP bridge deck. Unser said the results will be shared with federal, state and local officials, transportation departments and the civil engineering community so FRP composites will be more a "known" to them.

University of Tennessee, Knoxville (UTK) researchers and engineering students from the Fibres and Composites Manufacturing Facility are part of the bridge partnership. They embedded smart fibre optic sensors developed by Luna Innovations into the bridge surface during production. These high-density sensors are being used to monitor the composite deck system over time to give critical performance and safety data, thus providing a sustainable solution for aging infrastructures such as bridges. In addition, wireless technology developed at UT is being utilised for monitoring the response of the bridge system and traffic counts remotely via cloud computing.

"Lack of durability data is one of the major barriers of the adoption of novel and advance materials including carbon, basalt, or glass fibre reinforced polymeric composites in civil infrastructure," said Dayakar Penumadu, the Fred N Peebles Professor in the Tickle College of Engineering at UT and Characterisation Fellow for Materials and Processing for IACMI.

Penumadu added, "This is a major obstacle for integrating new materials and structures quickly and thus require successful demonstration as being done through this IACMI project. Bridge decks are the most damage prone elements, and we are integrating smart sensors distributed throughout the composite bridge deck that will provide us valuable performance data with time for years to come."

Led by IACMI, CAG, and the University of Tennessee, Knoxville, a collaboration of private companies contributed expertise and materials such as adhesives, epoxies, coatings and resins, preforms and reinforcements to the Morgan County bridge project. These include SCI, McKinney Excavating, Luna Innovations, Steffen Structural Engineering, Neel-Schaffer, Interplastic Corporation, Engineered Bonding Solutions, West System, Superior Fiberglass, METYX Composites and Compsys.