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Our built environment – from homes to offices, schools and shops – is not harmless to the environment. Buildings and the construction industry are, in fact, the world’s largest consumer of raw materials and contribute 25-40% of global carbon dioxide emissions (F. Pomponi & AJ Moncaster To clean. production 143, 710–718; 2017). Integrating buildings into a circular economy that minimizes the waste of materials could therefore bring huge environmental benefits. Conversely, a failure on this front could have disastrous consequences.

“Buildings can and should operate in a circular way,” says Francesco Pomponi, who studies the built environment at Napier University in Edinburgh, UK. “Otherwise there is no way out of the climate crisis.”

Take concrete, made by mixing gravel, cement and water. It’s the most widely used building material in the world, but it’s also a huge source of carbon, accounting for up to 8% of global man-made carbon emissions. Cement, of which more than four billion tons are manufactured each year, is the biggest contributor. Its production requires limestone (mainly composed of calcium carbonate) to be heated to produce lime (calcium oxide). The reaction releases CO2and even more CO2 is produced by burning fuel to generate heat.

Buildings as a positive force

Around the world, engineers, construction companies and architects are beginning to adopt and apply the circular model. There are many opportunities to improve the materials used in construction, to introduce circular design principles so that these materials can be properly reused and, even more ambitiously, to create buildings that make a positive contribution to the climate. and biodiversity. But a lot of work remains to be done if these huge emissions contributions are going to decline. And they have to come down – fast.

Innovations in materials could help make concrete a more sustainable option. Adding graphene – a 2D form of carbon – to the mix, for example, could improve the environmental footprint by strengthening the concrete and thus reducing the amount needed for a particular application. Sprinkling it into concrete could bring huge benefits, according to Nationwide Engineering, a company based in Amesbury, UK, which developed the mixture, called Concretene, in collaboration with researchers from the University of Manchester, UK. -United. The first building to benefit from Concretene was a sports hall in Amesbury in May 2021, which had new flooring laid using the material.

Concrete could even become a carbon sink. CarbonCure, a company based in Halifax, Canada, has developed technology that adds captured CO2 in the concrete. CO2 reacts with the calcium in the mix to form calcium carbonate, a mineral the company says adds strength to concrete while trapping carbon.

Concrete is already commonly reused – waste concrete is crushed to form recycled concrete aggregate (RCA), which can then be used to make new aggregate. But RCA tends to be used in low-tech applications, such as road fill. This reduction in the quality and value of concrete does not sit well with a fully circular economy.

Interior of a dimly lit building with brick walls.  Wet concrete is on the ground.

Concretene, a mixture of graphene and concrete, was used to make a roller disco floor in Manchester, UK.Credit: University of Manchester/National Engineering

CarbonCure is developing a new type of RCA that can be used in buildings. Sean Monkman, who leads the company’s technology development, says the same CO2– injection technology and subsequent mineralization can be applied to RCA as well as to freshly prepared concrete. Another company, Blue Planet Systems, based in Los Gatos, California, has developed an RCA made from recycled concrete waste and incorporating captured CO2.

At the Georgia Institute of Technology in Atlanta, the Kendeda Building for Innovative Sustainable Design uses CO2-store concrete as one of the sustainable innovations. The Kendeda project was built under the Living Building Challenge (LBC), a program that applies the “living building” designation to construction projects that meet a series of criteria, from responsible use of water to the supply of materials that eliminate waste. The program aims to incentivize buildings to produce energy, produce their own water and give back to nature more than they take from it, explains Shan Arora, director of Kendeda Building. There are 83 certified Living Building projects worldwide, and another 241 projects are registered to pursue certification.

Trying to meet LBC criteria, the Kendeda construction team salvaged the materials using local labor to intercept them as they were about to reach the landfills and then processed into suitable raw materials. “During the construction process, the Kendeda building diverted more waste from the landfill than it sent to the landfill,” says Arora.

The LBC project is extremely ambitious. “I see LBC as sort of the holy grail for regenerative building design,” says Nick Jeffries, who specializes in building innovations at the Ellen MacArthur Foundation, a charity based in Cowes, UK, who is dedicated to promoting the circular economy.

There are less ambitious, but still useful steps that can be taken alongside more holistic and demanding projects. In a rapidly warming climate, even windows can make a difference. In 2010, the iconic Empire State Building in New York City underwent a sweeping renovation, including an upgrade to all of the skyscraper’s 6,514 windows. The existing panes, rather than being scrapped, were each removed and the space within the double glazing was filled with an insulating gas – a mixture of argon and krypton. In addition, each pane has been covered with a transparent light-filtering film. These films, developed by scientists at the Lincoln Laboratory at the Massachusetts Institute of Technology in Lexington in the 1970s (JCC fan et al. Appl. Phys Lett. 25, 693; 1974), and now sold by Eastman Chemical Company, headquartered in Kingsport, Tennessee, use nano-sized metal particles to reflect heat. Renovated windows helped the Empire State Building use 40% less energy. Similar retrofits in other buildings will be crucial in a transition to circular building, says Jeffries.

Dismantling the problem

In a circular economy, says Jeffries, “buildings have to be constructed like Lego. You should be able to take them apart and reuse the structural elements.

Pomponi agrees that design is key, and thoughtful application of existing techniques can allow buildings to incorporate such flexibility. For example, rather than welding steel frames together to form the skeleton of a building, bolts can be used instead. “This allows for much easier dismantling when the useful life is coming to an end and much easier reuse of the structural section,” explains Pomponi.

“Even when materials with low environmental impact are used, a building can be designed in a non-circular way,” explains Caroline Henrotay, former coordinator of the Buildings as Materials Banks (BAMB) project, a Horizon 2020 innovation project funded by the European Union. If materials are, for example, glued together, Henrotay explains, “it will be more difficult to create clean fractions for high-quality end-of-life recycling.”

Such mechanical construction approaches are key to Wikihouse, a BAMB-supported UK project that provides the open source design of blocks that can be cut locally from birch plywood, allowing buildings to be assembled by inserting the pieces into place as in a puzzle. and easy to disassemble. The approach has been used to build places such as libraries around the world and homes in Almere, the Netherlands.

This type of reuse has an ancient legacy, says Jeffries. “The Theater of Marcellus [in Rome] continues after 2,000 years,” he says. “It was even used as a quarry to build bridges and local roads. It was really a bank of materials for future buildings.

A modern tool for tracking building components — and ensuring they can be reused in a meaningful way — is a “materials passport.” This document contains a detailed inventory of the materials used, as well as all data relating to the safety or origin of the material. With all of this data gathered, the components become a useful product at the end of that building’s life. A materials passport makes it easier to design a follow-up building, because the component specifications are known exactly in advance. The passport, says Jeffries, “recognizes that the material exists in a particular structure and then identifies the most useful future destination.” He cites an example of a building with such a passport that has already been dismantled for reuse: the temporary courthouse in Amsterdam, which was moved to a business park outside the city of Enschede at the start from 2022 to become an office building.

Coordinated material tracing

A number of start-ups are emerging to offer materials passporting services, but this could be confusing in the future. The LBC takes a broader view than just having a material passport, says Arora. The LBC also has a growing list of hazardous materials, the Red List, which should be avoided, such as asbestos, formaldehyde and chlorinated polymers, as they are harmful to human and environmental health. To be authorized in an LBC building, the materials must be listed and accounted for and also meet specific criteria. Given the range of ongoing projects, ambitions and definitions around the circular economy for buildings, its global adoption will take time. “I’m still trying to find out who owns the transition to the circular economy,” says Pomponi.

The mass adoption of circular economy practices will require enough decision makers to believe that such measures will not only help the planet, but that they will be economically feasible. “We need everyone. We need the Apples, the Googles, the Microsofts around the world to prove it can be done,” Jeffries says. With more than 200 companies in the Ellen MacArthur Foundation network, Jeffries wants to see them go beyond short-term goals. “We can go beyond doing less harm,” he says, and move toward the more affirmative goal of “reducing the materials we use, reducing emissions, reducing the waste generated, to buildings that actively purify the environment. ‘air, providing habitats for wildlife’.

Such ambitious advances in the design and construction of buildings will be essential for a sustainable global economy. Ultimately, the buildings that house and protect humanity will have to do more than provide a roof over our heads: by adopting innovative methods and materials, buildings could become a solution to the climate catastrophe that humans have invited.