A decades-long effort by Lawrence Technological University and the Michigan Department of Transportation to double the lifespan of highway bridges has been recognized as one of the 16 highest-value transportation research projects in the nation.
Research into the use of carbon fiber reinforced polymer (CFRP) strands instead of steel as a reinforcing material in concrete bridges was named to the “Sweet 16” top projects of 2020 by the American Association of State Highway Transportation Officials (AASHTO).
Research on the advanced material led by the MDOT and Nabil Grace, dean of LTU’s College of Engineering, began in 1988, with the construction of the nation’s first carbon fiber bridge, on Bridge Street in Southfield, in 2001. Since then, more than a dozen CFRP-reinforced bridges have been built across the state, including on busy sections of I-75, Gratiot Avenue and Eight Mile Road in the Detroit area.
Steel has historically been the go-to material for reinforcing and pre-tensioning concrete for highway bridges. Steel adds strength, but is prone to corrosion and deterioration under assault from extreme temperatures, water, and de-icing chemicals. Carbon fiber strands have a tensile strength comparable to steel, and although they’re more costly up-front, they resist corrosion and require less maintenance over time.
“CFRP has performed well in the field but its long-term durability wasn’t fully understood,” said Matthew Chynoweth, Chief Bridge Engineer and Director of MDOT’s Bureau of Bridges and Structures.
The research cited by AASHTO was conducted at LTU’s Center for Innovative Materials Research (CIMR), which offers advanced testing equipment such as boxcar-sized fire and freeze-thaw testing chambers. Over four years, carbon fiber components were subjected to 300 freeze-thaw cycles, combined fire and loading events, severe weather, and other trials.
The chief engineer on the four-year research project described the combination of Chynoweth, Grace, LTU’s laboratories and LTU’s students as unique.
“Sometimes you ride on waves of innovation, and sometimes you make the wave,” said Michael Townley, research project administration manager at the MDOT’s Bureau of Field Services. “I think in this case we’re really making the wave of innovation, thanks to Dr. Grace, Matt Chynoweth and LTU’s laboratory. To be able to build a bridge beam in a lab is a unique opportunity that Dr. Grace provides to his students, and the laboratory has equipment that allows us to test the material under extreme conditions. We’re grateful to Lawrence Tech for helping us be innovators and improve Michigan’s infrastructure.”
The data from this research confirm what proponents of CFRP have long theorized. Investigators found that CFRP strands held up well to conditions that simulated Michigan’s harsh weather. Moisture, rain, freezing rain, and extreme temperature swings did not significantly affect the material’s strength or mechanical properties over time. In addition, test results showed that some currently accepted parameters for CFRP are conservative and can be updated.
“We knew that it was a good material,” Townley said. “We have seen it perform well in the field. We just wanted to know a little bit more about long term durability. We found it has superior performance when it comes to standing up to Michigan weather and salt on the roads.”
Townley said the research goal is bridges that last 100 years. “I think we’re a lot closer to that now,” he said.
The research also generated guidelines, recommendations, and design examples that engineers and designers can use to build better bridges.
“Recently, AASHTO published its first design specification for CFRP pre-stressed concrete bridge elements, and this was mostly inspired by the work Dr. Grace has done for the past 30 years,” Chynoweth said.
The research also prompted a Japanese CFRP supplier, Tokyo Rope Co., to build a plant in Wayne County’s Canton Township, which Chynoweth said “has cut down on some costs and delivery times for CFRP.”
The state has also installed sensors on the carbon-fiber bridges, with funding now in place to monitor the bridges through 2025. Townley said the sensors “measure movement, stress and strain, and send the data to a location where it can be analyzed and compared to standards. We’ve been monitoring the material since 2001, and it’s been doing well.”
A summary of the report on carbon fiber reinforced polymers in bridge designs may be found at https://www.michigan.gov/documents/mdot/SPR-1690-Spotlight_676028_7.pdf, while the full report is available at https://www.michigan.gov/documents/mdot/SPR-1690-FinalReport_663701_7.pdf/. For more details on Michigan’s bridges, visit www.Michigan.gov/Bridges.
Lawrence Technological University, www.ltu.edu, is a private university founded in 1932 that offers more than 100 programs through the doctoral level in its Colleges of Architecture and Design, Arts and Sciences, Business and Information Technology, and Engineering. PayScale lists Lawrence Tech among the nation’s top 11 percent of universities for the salaries of its graduates, and U.S. News and World Report lists it in the top tier of best Midwestern universities. Students benefit from small class sizes and a real-world, hands-on, “theory and practice” education with an emphasis on leadership. Activities on Lawrence Tech’s 107-acre campus include more than 60 student organizations and NAIA varsity sports.