A decade ago, conversations about infrastructure mainly revolved around the need for additional funding to repair it. But those discussions have evolved, increasingly emphasizing the need for sustainability and resiliency in projects that involve building or rehabilitating the nation’s roads, bridges, ports, power grid and more.
The composites industry can provide the sustainable solutions that states seek. With increased funding, like that proposed in the $1.2 trillion infrastructure bill (see sidebar), state agencies would have more money and more opportunities to test innovative technologies and construction techniques.
“There are so many examples around the country, whether it’s bridges or reinforced building structures, where utilization of composite innovation has been demonstrated to be effective,” says Greg Nadeau, chair and CEO of Infrastructure Ventures. “The huge investment in the infrastructure bill for bridges over and above the regular allocation does present an opportunity for states to use those funds to expand the use and understanding of these alternative materials. They’re not experimental; they’re proven.”
Building Better Bridges
Composite materials are already being used to build more resilient bridges. Coastal states and northern states that use road salt during the winter have seen their bridges decay due to the corrosion of the steel in reinforced concrete and pre-stressed concrete structures. Using non-corrosive materials like composite rebar can reduce the amount of money that state Departments of Transportation (DOTs) must spend on bridge maintenance and repair.
“Ordinarily a conventional bridge rated at [a lifetime of] 75 years has to be substantially addressed over a period of 40 or 50 years. With a non-corrosive at the base of your material selection, you extend life and you reduce long-term lifecycle costs,” says Nadeau. “You are building a bridge that you literally won’t have to worry about generationally, and that’s an extraordinary opportunity.”
There are other cost savings as well. “The composition of the concrete can be different if we have a material that does not corrode. For example, we don’t have to use corrosion inhibitors, which can cost about $50 per cubic yard,” says Antonio Nanni, professor and chair of the Department of Civil and Architectural Engineering at the University of Miami.
Bridges built with composite materials can be designed with more streamlined support structures. “With concrete, you’re spending a lot of your money and resources to build that bridge to hold itself up, not on its function, which is to carry traffic,” says Ken Sweeney, president and chief engineer at Advanced Infrastructure Technologies (AIT). “If you can lighten that up and have a higher strength-to-weight ratio, it’s a huge benefit; the construction is less costly.”
Since composite rebar is significantly lighter than steel rebar, it takes fewer trucks to transport the bars (or bridge components made with composite rebar) to the jobsite. That reduces CO2 emissions. Contractors can use smaller, less costly cranes to lift composite bridge components into place, and they’re easier and safer for construction workers to handle.
FRP Bridge Innovations
State DOTs looking to assess the performance of composite materials in bridges have a wide range of old and new projects from which they can choose.
Marshall Composite Technologies used its C-BAR® rebar in 1996 to reinforce the concrete deck of Buffalo Creek Bridge in West Virginia. It was the first time FRP rebar had been used for a vehicular bridge in the U.S., and the composite deck is still performing well.
GFRP rebar is typically made through a pultrusion process that cures the material as it is pulled out of the equipment in a straight line. Marshall Composite Technologies has developed an innovative technology that skips that pultrusion curing stage.
“It allows us to go at four to five times the speed of traditional pultrusion, because we’re not limited by having to cure inside a mold,” explains Tom Ohnstad, director of engineering. “After we have formed the rebar with the ribs, we can go straight into the final oven and cure it, or we can bend it and then put it in an oven and cure it.” Moving from a continuous process to a batch process has enabled the company to provide rebar in the custom curved or bent shapes that construction projects often require.
Creative Pultrusions, part of the Creative Composites Group, used pultruded composites to build the world’s largest FRP, clear-span, pedestrian bridge during the last two years. The 152-foot long, box truss structure, part of the company’s E.T. Techtonics line, connects two sections of a 22-mile trail built on an abandoned rail bed in Bermuda.
Creative Pultrusions designed and engineered the composite structure, manufactured samples of the bridge’s unique connections and components and then sent them to the University of Miami and West Virginia University for testing. Once the design was finalized, technicians at Creative Pultrusions pultruded the bridge in sections no longer than 39 feet, since they had to fit into shipping containers for the journey to Bermuda.
Prior to shipping, the company assembled and tested the bridge on its own site to ensure it met the strength and stiffness requirements. That initial build also ensured that the crane in Bermuda could handle lifting the bridge into place. The bridge owner participated in this trial construction, which was fortunate because no one from Creative Composites Group could travel to Bermuda to oversee construction during the pandemic. Final construction of the bridge in Bermuda, which took place during December 2020, went smoothly and quickly.
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.