Grist Mill Bridge in Maine, first to use FRP tub girders, opens to traffic

New bridge is the first in the nation to use fiber-reinforced polymer (FRP) tub girders called GBeams

May 26, 2021 / 2 minute read
Grist Mill Bridge in Maine, first to use FRP tub-girders, opens to traffic
Image: University of Maine

The Maine Department of Transportation (MaineDOT) recently opened the new Grist Mill Bridge in Hampden.

The 75-ft-long, single-span bridge carries Routes 1A and 9 over Souadabscook Stream. The total cost for the project is approximately $9 million. The contractor on this project was T. Buck Construction out of Turner.

The new bridge is the first in the nation to use fiber-reinforced polymer (FRP) tub girders called GBeams. The patented GBeam technology is the result of research and development at the University of Maine (UMaine) Composites Center, which licensed the technology to Advanced Infrastructure Technologies (AIT) Bridges, the university's commercialization partner for this technology. Funding for the research was provided by the U.S. Army Corps of Engineers Engineer Research and Development Center (ERDC) and the U.S. Department of Transportation (U.S. DOT) through the Transportation Infrastructure Durability Center led by UMaine. The GBeams used in the Grist Mill Bridge project were manufactured at the AIT Bridges facility in Brewer.

The GBeam technology is corrosion-resistant and designed to last more than 100 years with little to no maintenance, according to MaineDOT. The composite girders are lightweight: they weigh as little as one-quarter the weight of steel girders. The department says the GBeam technology is a sustainable, low-cost alternative that is easy to install.

"The big draw here is durability," MaineDOT Commissioner Bruce Van Note said in a statement. "Time will not take quite the same toll on the composite tub girders in this bridge. We expect this structure will need less maintenance over time and may last 25 years longer than its conventional counterparts. At MaineDOT, we believe sponsoring this new technology now will yield long-term benefits for Maine taxpayers and travelers."

The University of Maine field-load-tested the Grist Mill Bridge with support from the MaineDOT and U.S. DOT. The bridge was successfully tested with more than 260,000 lb of load carried by four MaineDOT trucks. The two-day testing provided baseline performance data allowing UMaine researchers and AIT Bridges to refine the GBeam design.



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