For decades, the Michigan Department of Transportation (MDOT), in conjunction with local universities, has been working to double the service life of highway bridges using new materials technologies, a project recognized as one of the 16 most valuable transportation research projects in the United States.
Lawrence Technological University (LTU) in Southfield, Michigan, conducted research using carbon-fiber-reinforced composite cables instead of steel reinforcement as a reinforcement for concrete bridges. The project was named one of the Top 16 Best Projects of 2020 (Sweet 16) by the American Association of State Highway and Transportation Officials.
The project was initiated in 1988 under the direction of Nabil Grace, dean of MDOT and LTU's College of Engineering, and in 2001 the first carbon-fiber-reinforced bridge in the United States was built on Bridge Street in Southfield. Since then, more than a dozen reinforced bridges, including I-75, Gratiot Avenue and Eight Mile Avenue, have been constructed in Michigan.
As a conventional material used to reinforce highway bridges and apply prestressing to concrete, steel is susceptible to corrosion and deterioration when exposed to temperature extremes, moisture and de-icing chemicals. The tensile strength of carbon fiber cables is comparable to steel, and while their upfront cost may be higher, they are more resistant to corrosion and require less maintenance in service.
"In bridges, CFRP performs well, but its long-term durability properties are not well understood," said Matthew Chynoweth, chief engineer and supervisor of bridges for MDOT's B
The research was conducted at LTU's Innovative Materials Research and Development Center, where carbon fiber components have been subjected to 300 hot and cold cycles with simultaneous flame and load application, severe weather and a variety of other performance tests over the past four years.
Even under test conditions that simulated Michigan's harsh weather, CFRP performed well, with moisture, rain, freezing rain and extreme temperature changes failing to affect its strength and other mechanical properties. The test results indicate that the current industry-accepted performance specifications are already too conservative and can be updated.
The goal of the project was to develop bridges with service lives in excess of 100 years. The project also gives guidelines, recommendations and design examples for use by engineers and designers.
The project prompted Japanese CFRP supplier Tokyo Rope to establish a plant in the town of Canton. The sensors are able to monitor the displacement and stress conditions of the bridge in real time, as they are pre-implanted in the carbon fibre bridge.
