Recycling concrete sustainably

The production of cement, the material that binds concrete, is very stressful for the environment and is alone responsible for 5 to 7 per cent of global CO2 emissions.

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Johannes Tiefenthaler, a doctoral candidate at Zurich’s University of Applied Sciences (ETH), fills a reactor with crushed concrete.

Concrete is worn out after 50 to 100 years and is then recycled. It is crushed and the coarse granulate is then re-used as gravel in new concrete. “But that’s not a good solution because you get lower-quality concrete,” says Tiefenthaler, who is studying at ETH Zurich’s Institute of Process Engineering. “Making new concrete with recycled granulate requires more cement than normal concrete to ensure good quality. That produces more CO2 emissions.”


"I find it exciting to work on finding a solution to a politically provocative issue.”

Johannes Tiefenthaler, doctoral candidate in Process Technology, ETH Zurich


Working for SCCER EIP, the research competence centre for efficient industry processes, Tiefenthaler is investigating how concrete can be recycled more sustainably. Here is his idea: during carbonisation, CO2 should remain permanently in the form of lime in the recycled material. This reduces porosity, making the material harder and more easily workable. At the same time, less cement is needed to produce fresh concrete, thereby reducing CO2 emissions. “That may not solve all the industry’s environmental issues, but it does lick a substantial part of the problem.”

Last modification 26.07.2019

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