The AIT bridge system -- also called Bridge-in-a-Backpack (pictured) -- uses lightweight tubes made of fiber-reinforced plastic that are strong enough to support a roadway after they’re filled with concrete.
- These fabric tubes are inflated and treated with resin. It takes just 30 minutes to harden and shape spans of up to 90 feet. These form the arches of the bridge.
- After the arches are placed in position (no heavy lifting required), corrugated panels are bolted onto the curved tubes.
- Cement is then poured into the tubes, setting in two to four days. (Traditional concrete structures take two months to build.) No steel rebar needed.
- Once the plastic panels and tubes are in place, the span is covered with sand and gravel, and then compacted and paved.
You can watch a video of how these arch bridges work.
These concrete-filled, carbon fiber reinforced polymer composite tubes also protect from corrosive factors like weather or salt. And according to simulation tests, these structures can withstand 50 years of heavy truck traffic.
While the materials cost more than precast concrete, speedier construction saves money. Also, a shortage of concrete materials makes these sorts of designs more appealing.
So far, AIT has constructed 13 bridges -- most in Maine, Massachusetts, and Michigan -- and they’ve raised $2 million in seed funding. But the 5-employee company will need to convince buyers that they’ve built a better bridge.