A decades-long effort by a local 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.
Lawrence Technological University in Southfield conducted research on the use of carbon fiber reinforced polymer strands, rather than steel, as a reinforcing material in concrete bridges. The project was named in the Sweet 16 top projects of 2020 by the American Association of State Highway Transportation Officials.
Research on the material was led by MDOT and Nabil Grace, dean of LTU’s College of Engineering. The work began in 1988, and the construction of the nation’s first carbon fiber reinforced bridge on Bridge Street in Southfield was completed in 2001. Since then, more than a dozen similarly reinforced bridges have been built across the state, including on sections of I-75, Gratiot Avenue, and Eight Mile Road.
Steel, which is prone to corrosion and deterioration when exposed to extreme temperatures, water, and de-icing chemicals, is the historic go-to material for reinforcing and pre-tensioning concrete for highway bridges. Carbon fiber strands have a tensile strength comparable to steel. They are more costly upfront but resist corrosion and require less maintenance over time.
“CFRP has performed well in the field, but its long-term durability wasn’t fully understood,” says Matthew Chynoweth, chief bridge engineer and director of MDOT’s Bureau of Bridges and Structures.
The recognized research was conducted in LTU’s Center for Innovative Materials Research, 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.
“Sometimes you ride on waves of innovation, and sometimes you make the wave,” says Michael Townley, research project administration manager at 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 CFRP strands held up well to conditions that simulated Michigan’s harsh weather. Moisture, rain, freezing rain, and extreme temperature swings did not affect the material’s strength or mechanical properties over time. Test results showed that some currently accepted parameters for the material are conservative and can be updated.
“We knew that it was a good material,” Townley says. “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.”
The research goal is to create bridges that last 100 years. The research also generated guidelines, recommendations, and design examples that engineers and designers can use.
“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 Canton Township.
The state has also installed sensors on the carbon-fiber bridges, with funding now in place to monitor the bridges through 2025. The sensors measure movement and stress.
LTU is a private university that was founded in 1932.