Popular Science takes us over a bridge built inside a Fribourg, Switzerland, laboratory entirely out of re-used concrete – a thrifty construction technique that could help cut concrete’s hefty contribution to greenhouse gasses:
“The idea that the walls of a building could become a footbridge—to our knowledge, this is completely new,” says Corentin Fivet, an architect and structural engineer at [École Polytechnique Fédérale de Lausanne], and one of the bridge-builders.
You likely don’t give much thought to the concrete beneath your feet and towering all around you, but there’s ample reason to worry about it. This basic building block of the modern world is also a sleeping giant contributing to climate change. As of 2018, concrete production accounts for as much as 8 percent of the globe’s carbon emissions. The much-maligned aviation sector produces less than half that amount.
Today, architects and builders aren’t typically used to ringing up demolition companies in search of material. But that’s what the bridge-builders did. Within two weeks, they had found a renovation site that would provide concrete blocks to their liking: 20 centimeters (7.9 inches) thick, complete with holes that allow the blocks to be reinforced and strengthened with hefty post-tensioning cables.
“We didn’t want thinner walls, because the arch needed that thickness to withstand the loads,” says Fivet. “Also, we didn’t want heavier, or thicker walls, because it would be a wasteful way of reusing those walls or slabs.”
The bridge-builders then tested concrete blocks with a tool called a rebound hammer, essentially pounding the concrete to measure its strength. They partnered with a firm to scan the concrete in order to judge, for instance, how much it had reacted with carbon dioxide in the air (over time, one of the major causes of corrosion in concrete).
Even though humans have reused building materials for thousands of years, the demolition firms who’d handle old materials are typically nowhere to be found in builders’ conversations. There’s a widespread belief, according to Fivet, that using such blocks isn’t reliable because it’s hard to know how strong a given piece of concrete actually is, especially after it’s been undergoing wear and tear for years.
Yet Fivet believes that modern testing methods have made it possible to do just that without destroying the material.