The New York Times has a report on a candidate for the ‘bridge of the future” title: the Neal Bridge in Pittsfield, Maine, that has a foundation of 23 hollow carbon- and glass-fiber fabric arches, filled with concrete. These are 12-inch-diameter tubes that have been inflated, bent to the proper shape and stiffened with a plastic resin. They are then installed side-by-side and stuffed with concrete, “like giant manicotti.” Covered with composite decking and compacted soil, the arches support a standard gravel-and-asphalt roadway.
Fiber-reinforced plastic strips and sheets have been used in the past to repair concrete or steel on existing bridges, or to strengthen structures against earthquakes. Glass-fiber rods have replaced steel in some reinforced concrete work, because corrosion of steel rebar from road de-icing chemicals destroys concrete.
Others have been demonstrated that use a “hybrid composite beam” technology that looks somewhat similar to traditional bridge girders.
John Hillman, an engineer and president of HC Bridge Company in Wilmette, Ill., has developed straight beams that combine polymers with concrete and steel. The basic beam consists of a rectangular FRP tube with an arch-shaped conduit formed inside it. The conduit is filled with concrete, which provides compressive strength, and steel rods along the bottom of the tube provide tensile strength. The beams have been used on a test railroad bridge in Colorado and several road bridges in Illinois and New Jersey.
“Everything about the beam is designed to be compatible with conventional means of construction,” said Mr. Hillman, who has been working on the design for 14 years. “We’re very close right now to parity with concrete and steel on an installed-cost basis.”
The Neal Bridge design, however, is a departure from these hybrid girder construction and uses little of the relatively costly-FRP material. The FRP it does use serves largely as a shell for the less-expensive concrete. The tubes help protect the concrete from de-icing chemicals, potentially reducing maintenance costs. Also, no internal rebar is needed.
The technology behind the tube-bridge structure is a product of the University of Maine’s Advanced Engineered Wood Composite Center. A spinoff comany, Advanced Infrastructure Technologies, is working to develop and commercialize applications for what has been dubbed “bridge-in-a-backpack” technology.
In an interview earlier this year with the Bangor Daily News, AEWC director Habib Dagher said, “This is a milestone because of how exciting this technology is. It has the potential to change everything in terms of bridge construction. It can change the way bridges are built in the future.”
AIT plans to continue to work with HC Bridge, and Maine officials said the endeavor could create about 100 new jobs and lead to at least six new bridges in Maine over the next several years.
The bridge in Maine has been standing for nearly one year, and cost less than $600,000 to build.