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Concrete mixed using recycled materials

Is a house recyclable? In principle, yes. RISE is participating in a project to produce concrete from construction and demolition waste for use in new buildings.

Concrete production is far from a climate-smart process. As part of the RE4 project, RISE is investigating the possibility of recycling demolition waste to replace current forms of ballast – the structural element in concrete.

"Concrete is usually manufactured using sand or gravel taken from natural sources, for example by blasting and crushing rock. We are now using demolition waste from old houses as ballast,” says RISE research scientist Linus Brander, who is responsible for the project.

By employing robots to sort through demolition waste, those elements that are suitable for use in new concrete can be identified while, at the same time, plastic, timber, glass and other materials can be recycled in other types of building materials. In parallel with this, we are looking into areas such as how brick can be used as an alternative binding agent in cement and how plastics and timber can be used as insulation.

“Today, when we tear down a building the demolished materials are simply driven away and thrown on a pile in landfills or at best used as low-value filling mass on building sites, while at the same time we extract new materials from natural sources. If instead this material can be recycled in building products, we can achieve a circular flow,” says Linus Brander.  

RISE’s primary role in the project is to develop various types of concrete. Demolition waste from France, Germany, Norway and the United Kingdom is tested and characterised, firstly in the laboratory and then in a concrete works.

"British houses are more often built of brick than those in Sweden. Another crucial factor, given that concrete is mixed with water, is that bricks vary in quality and absorb more or less water. This is quite a sensitive process; the end result must be able to cope with both the demolition waste and the requirements of the workers casting the concrete,” says Linus Brander.

RISE is also conducting a lifecycle analysis of the environmental impact of this type of concrete construction calculated on the building’s working life.

“Here, we calculate everything from carbon dioxide emissions and energy consumption to wasted resources. Recycling may intuitively feel more environmentally friendly; however, it may lead to more transports, for example. Concrete companies generally have access to ballast locally, while many buildings are demolished in large cities, meaning that the material must be transported to the factories,” explains Linus Bender.     

The RE4 project will continue until the start of 2020 and the intention is to spend 42 months building two energy-efficient demonstration houses consisting of 65% recycled materials; one in Northern Ireland and one in Spain.