Maybe it's not surprising that a city that's experimenting with building roads out of recycled plastic is also building plastic bridges.
Rotterdam, the second-largest city in the Netherlands, is filled with canals and split in half by a river—and along with all of that water, it has 850 bridges for pedestrians and cyclists. As the bridges wear out, the city is replacing them with plastic instead of steel, concrete, or wood.
Using fiber-reinforced polymer, a lightweight plastic, makes it possible to install a pedestrian bridge in as little as an hour. "It's a light material, making it really easy to put it out there," says Dave Geensen, project manager for the city. "A normal wooden bridge or steel bridge will take up to three weeks of construction. With this bridge, in the morning the truck with the bridge came, and in the afternoon, before lunchtime they had already left. The bridge was there."
The most recent bridge, installed in January, is also incredibly thin: although it's 65 feet long and about six feet wide, it's less than 10 inches thick. It's more than three times lighter than a comparable concrete bridge, and less than half the weight of a similar bridge made of steel.
Using plastic also has environmental advantages, because steel and concrete take about twice as much energy to make. Manufacturers are also experimenting with plant-based resin. "We believe it’s a matter of time before biological features will be the new standard when it comes to resin," says Geensen.
While a wooden bridge might last 25-30 years before it has to be replaced, a bridge made from composite is expected to last as long as 100 years. Unlike metal bridges, the new bridges won't ever rust, and they're simple to repair.
The city started installing the first plastic bridges in 2009, and now has around 90, more than any other city in the world. "We did the math and we were convinced that composite bridges were a smart solution," he says. "Our main goal was to construct bridges using materials which require the lowest possible maintenance costs and could last longer than a lifetime."
The bridges feel a little strange to walk on. "It may feel a bit wobbly at first," he says. "That's something you have to get used to. But we haven't had any complaints about it."
Rotterdam, which is experimenting in all areas of infrastructure, uses its city budget to push industry for cutting-edge designs. "We can make a big difference when it comes to new innovations," says Geensen. "We're very aware of that. If we always stick to the same solutions, we won't be getting the infrastructure branch an impulse which is needed to experiment."