Demolished buildings offer new home for CO2 emissions

A staggering 30 billion tonnesExternal link of concrete are used every year worldwide – and the resulting greenhouse gas emissions are equally colossal: more than those of international aviation and buildings combined. A Swiss company believes it has a solution to help the concrete industry decarbonise and permanently remove one million tonnes of CO2 by 2030. This may be a fraction of what is needed, but it’s an important step.

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The Swiss firm Neustark has developed a method to turn concrete waste from demolished buildings and roads into a carbon sink to permanently remove CO2 from the atmosphere. Their process uses CO2 captured from biogas plants which is liquefied and transported to nearby demolition sites.

There the CO2 is injected into concrete granules from a demolished building using a purpose-built tank and other technology. This triggers a mineralisation process similar to injecting CO2 deep underground. The CO2 is permanently bound in the pores and surface of the granules.

The carbonated granules can then be used by recyclers to build roads or to make concrete for new buildings or other purposes.

Mineralisation is the most durable method of carbon removal known to date. The risk that the stored carbon is released again into the atmosphere is negligibleExternal link. Only temperatures of 600°C or very strong acids are able to release that CO2.

Swiss Federal Laboratories for Materials Science and Technology (EMPA) foundExternal link that CO2-injected concrete also has higher compressive strength than traditional concrete. This opens the door to reducing the amount of cement that is mixed with sand and gravel to make concrete, and the associated CO2 emissions.

Together with partners, Neustark now has 17 carbon removal and storage plants in operation in Switzerland and Germany with a capacity to remove over 5,000 tonnes of CO2 a year. More than 30 additional plants are under construction across Europe.

The spin-off from federal technology institute ETH Zurich has big ambitions: to ramp up and broadly deploy its technology within existing facilities of concrete producers with the goal of removing one million tonnes of CO2 by 2030. In September 2023, Neustark signed a partnership deal with the cement giant Holcim, which committed to rolling out the innovative CO2 storage technology at its construction demolition sites worldwide.External link