Bridge in a Backpack

Bridge in a Backpack

One of the more widespread uses of carbon fiber in the construction world is bridge-wrapping. Externally reinforcing existing bridges, even with an expensive material like carbon fiber, is a fast and cost-effective way of extending the service life of an older bridge, or increasing earthquake resistance.

Among the most innovative uses of carbon fiber, however, is a design for building new bridges. The “Bridge in a Backpack” was developed over the course of nine years by The University of Maine, and is being commercialized in partnership with Advanced Infrastructure Technologies (AIT Bridges). It is designed for new construction and replacement of small and medium span bridges, and offers speedy construction and excellent resistance to corrosive environments. In fact AIT boasts a 100-year service life.

The system is based on tubes made of braided carbon and glass fibers, 12-15 inches in diameter. The tube is sealed at the ends and inflated. In its inflated state, it is bent into an arch of the appropriate arc, then infused with polymer. When the polymer cures, the tube is permanently stiffened into an arch.

The light weight arches are shipped to the job-site hollow. They are so light that four people can carry one.

In situ, they are erected in position and covered with corrugated composite decking. Then the tubes get pumped full of concrete. They can be filled from a hole at the apex of the arch, using a flowable mix of self-consolidating concrete (SCC). Once the concrete has hardened, the span is achieved; the deck and the rest of the bridge can be finished on top of it. Bridges have been erected in as little as two weeks.

The carbon-and-glass fiber outer layer is both stay-in-place formwork and reinforcement for the concrete. The arches can span up to 65 feet. According to AIT, “All designs are engineered to exceed AASHTO load standards for single span bridges from 35 ft. to 65 ft.”  You can asee a good, shirt video about it here.

The creator of the Bridge in a Backpack, Habib Dagher, founding director of UMaine’s Advanced Structures and Composites Center, was honored by the White House last year as a “Transportation Champion of Change.”

Bridge in a Backpack technology has been used on a number of bridges, mostly in the Northeastern US. The first successful use was in 2008.

All images via AIT.