Altogether the rafts feature 31,000 pounds of vinyl ester resin, reinforced by 78,000 pounds of mat, biaxial and double bias fiberglass. Fillers include a UV inhibitor and a “Federal Gray” pigment that helps the rafts subtly mimic the timber that would be placed on top. In addition, steel post-tensioning rods were passed through each pair of pontoons to help clamp the pontoons together during the final raft assembly, as well as to provide redundancy to the bonded joint.
Production was both big and fast. Each pontoon had to meet an aggressive one-week start-to-finish production schedule.
Overall, it was a very forward-thinking approach to keeping a historic structure intact. Whether walking, fishing, swimming or driving, visitors using the bridge today may be more focused on the structure’s connection to history. But without the pontoons, the bridge might not have had a future.
“[The rafts] are decked over with a significant amount of timber in order to make the bridge look like what was there before, from the historic preservation perspective. Very little of the composite raft is visible; from the side you can see about a foot of the pontoon,” Marquis says. “But the pontoons themselves make up not only the flotation for the bridge – they are essentially the structural backbone of the bridge.”