Using prefabricated components provides a safety and cost-saving advantage that DOTs should consider when they look at the total cost of bridge projects, says Dustin Troutman, director of marketing and product development. “The longer you’re on a bridge or a job site, the higher the risk of accidents.”
AIT has built 30 bridges across the country using its GArch™ composite bridge system, which includes curved FRP tubular elements and FRP decking. In late 2020, the company introduced a new technology, GBeam™ composite tub girders, to construct the Grist Mill Bridge in Maine. AIT worked with the University of Maine and the state DOT to develop the GBeams, which incorporate carbon fiber and glass fiber in the bottom flange and glass fiber in the top and can be fabricated up to 120 feet.
Grist Mill Bridge’s eight, 75-foot-long composite girders are replacements for steel girders. Because of the GBeams’ lighter weight, the contractor was able to use a much smaller crane to lift them into place. In addition, the contractor put two of the GBeams together and pre-installed all the utilities that had to run under the bridge in the channel between them. It’s much safer to have the work done on shore rather than having workers installing the necessary piping and wiring while working over the river.
Although the GBeam technology is more expensive today than steel girders, Sweeney expects it will become more cost competitive over time through efficiencies in processes and manufacturing. He also notes that the composites supply chain has been much less volatile than the steel supply chain, which has seen increasing costs and long delivery times.
Another material that could impact the composite bridge industry is rebar made with basalt. The basalt material derives from lava rock that is melted down and formed into fiber strands, which can then be chopped.
“Within the composites’ family, E-CR glass fiber remains the most used fiber type because of its availability and low cost. However, the interest in basalt fibers has been growing since their physical properties exceed those of glass and the cost difference is marginal,” says Alvaro Ruiz Emparanza, director of engineering and business development at Mafic. “In terms of performance, basalt has higher tensile strength and modulus of elasticity than E-CR glass, but its properties are definitely not as high as carbon fiber.” He notes that basalt fiber might be particularly useful in pre-stressed composite structures.