ECOLE Polytechnique Federale de Lausanne (EPFL) researchers in Switzerland have built a footbridge prototype using reinforced-concrete blocks from walls of a building being renovated.

The blocks were assembled into a prestressed arch. This project, which marks the first time concrete has been reused in this way, is part of an initiative to substantially shrink the construction industry’s carbon footprint by adopting a circular economy approach. The footbridge was inaugurated at a ceremony at the Smart Living Lab in Fribourg on Oct. 11.

For concrete to be reused effectively, new design methods are needed that are based on exploiting existing concrete sections, rather than the conventional approach of pouring fresh concrete in line with each project’s specifications. The catch is that the properties of existing sections can vary and are not always known ahead of time. To help engineers employ these new methods, the Structural Exploration Lab (SXL) recently developed a computer program that automates the process of selecting reclaimed elements from a given stock and minimizes a new structure’s carbon footprint.

In practice, builders are often reluctant to reuse concrete due to the perceived additional risk. But the SXL team believes there are only benefits. That’s where their project of building a footbridge prototype comes in: to demonstrate, quickly and efficiently, that the procedure is safe and relevant. “We gave ourselves two months to find a source building in the region and a demolition company that would be interested in working with us,” says Bastien Masse. That company turned out to be Diamcoupe, which had been commissioned to renovate a building erected less than 10 years ago; this renovation site was the perfect opportunity to source viable blocks of concrete. “We asked Diamcoupe to cut the concrete into the sizes we needed and to drill holes through them for our prestressing cables. These cables were provided by Freyssinet and used to build the arch,” she adds.

The engineers were thus able to obtain 20cm-thick concrete blocks for the footbridge. They added mortar in places to smooth out the slight differences in dimensions, which are inevitable anytime objects are reused. “Arches are actually the ideal structure for repurposing concrete blocks, since the material is the only subject to compression forces,” says Jan Brutting, a graduate from SXL who initiated this project.

This project, which received funding from an ENAC Innovation Seed Grant, opens up promising new research horizons for SXL. (SD-Agencies)