Making construction sustainable by reusing materials

Some 17 million tons of construction materials (excluding excavated soil) are thrown away in Switzerland every year. “These materials are generally in good condition and could be reused, preventing us from having to manufacture new ones,” says EPFL professor Corentin Fivet. “Especially since the production processes – which include extracting natural resources – generate a lot of pollution.” Fivet heads the Structural Xploration Laboratory (SXL) at EPFL’s School of Architecture, Civil and Environmental Engineering (ENAC). He will take over as the academic director of the Smart Living Lab in Fribourg on 1 April 2024, and this is one of the research areas he will focus on.

“Reusing construction materials is just good common sense,” he says. “It was standard practice before the industrial revolution, because making materials from scratch cost so much more. Today, unfortunately, that’s no longer the case. It’s actually just the opposite – it’s now more expensive to reuse materials, since that’s not part of the routine. And for investors, anything that comes with new risks also comes with a higher cost.” Yet the main driver for making the switch today isn’t economic, but environmental.

If we’re serious about cutting emissions, we can’t just reuse the flower pots and carpet.

The reuse of materials has been gaining traction over the past decade with the emergence of the circular economy. A number of reconversion initiatives are being rolled out in Switzerland, such as plans to turn a former Fiat plant in Geneva into a combined residential and commercial district. Architects have already recovered many components from the old plant, such as the urban furniture and structural elements – including some concrete slabs that are now part of the building housing the Smart Living Lab. “It’s still a niche market and we need to gain more experience, run more technical and economic feasibility studies, and collect more evidence to demonstrate that used construction materials still have value and can be employed in place of new ones,” says Fivet.

Research has already shown that reusing load-bearing structures can bring significant environmental benefits, as these structures are used in large numbers and manufacturing them is a highly polluting activity. “If we’re serious about cutting emissions, we can’t just reuse the flower pots and carpet,” says Fivet. It’s always more sustainable to use something that already exists, even if it was environmentally un-friendly to produce. A recent SXL study found that reusing concrete slabs generates up to 90% less greenhouse gas emissions than manufacturing new ones.

A multi-faceted approach

Beyond the benefits to the construction industry, reusing materials creates a virtuous circle because it supports the local economy and creates new types of jobs at all skill levels. “Workers have been trained on how to build things, but not how to take them down,” says Fivet. “But to reuse materials properly, we need competencies in an array of areas. New, locally focused companies and non-profit organizations are being created every month and have very different business models.” For instance, several websites are popping up for people looking to acquire or dispose of elements like sinks, doors, radiators and furniture.

The trend is also driving change in education. “Sustainability specifications have become so demanding that we can’t teaching building methods the same way today as we did just ten years ago,” says Fivet. “We need to introduce alternative approaches and rethink our standard way of doing things.” In addition to SXL, several other ENAC labs are investigating the reuse of construction materials. EAST is examining how they can be incorporated into the design process; THEMA is studying the environmental impact of materials by drawing lessons from the history of construction; HERUS is assessing how materials can be distributed across a city; EESD is developing a process for making walls from waste concrete; CRCL is looking at how robotics can automate construction processes, including through the use of recycled materials; and RESSLab is analyzing the mechanical properties of recovered steel.

Not a green light

However, Fivet stresses that being able to reuse construction materials shouldn’t be taken as a green light to erect buildings at will. “Our research has proven that materials can be reused, but that doesn’t mean we can give carte blanche to property developers. It’s similar to the problem we’re seeing with plastic bottles – people think that since they can be recycled, there’s nothing wrong with using them just as before.” He goes on to say that the first step in shrinking the construction industry’s carbon footprint is to preserve existing buildings. If buildings must be demolished, then architects should try to reuse as many of their components as possible, aiming to conserve the materials’ physical properties. Recycling should be considered only for any remaining components, since recycling processes generally require a lot of energy and generate more pollution than reuse does.

Our research has proven that materials can be reused, but that doesn’t mean we can give carte blanche to property developers.

That said, there are limits to the reuse of construction materials. In Switzerland, for example, six to seven times more buildings are constructed than demolished. Property developers need to build fewer buildings and, especially, build them more responsibly. That means not replacing existing buildings by ones that are essentially the same, or that are bigger and more modern but can only accommodate the same number of occupants. “Such decisions make no sense in light of the efforts needed to combat global warming,” says Fivet. “That’s clear to scientists, but we still need to make it clear to property developers and the general public.”

Waste no more: Talk by Corentin Fivet followed by a panel discussion, 6pm on 27 March 2024, SG 1138.