Carbon negative concrete




In recent years, Snøhetta has conducted research on different materials that are central to building and production, and in the early summer of 2020, the idea of creating a carbon negative concrete was planted. After a summer of small-scale testing, Snøhetta teamed up with some of Norway’s most experienced contractors, researchers, producers and suppliers within the concrete and biochar industry. The collaboration resulted in the first carbon negative precast concrete wall being cast in March 2021. After thorough testing and evaluation, the material will now be used in the very first building project just outside Oslo, Norway.

Technical details

Education & Research, Sustainability
Oslo, Norway

Con-Form, Skanska, Norsk Biokullnettverk, Oplandske Bioenergi, Betong Øst, NTNU – Norwegian University of Science and Technology

Photo: Ketil Jacobsen

Full-scale test

The amount of biochar incorporated in the concrete practically limits the achievable strength level of the concrete, and the properties of the concrete were tested in a full-scale production concrete wall elements. The wall was designed as shell elements where the core was cast out after installation to form solid, load-bearing walls. The amount of biochar used in the core concrete between the shell elements was adapted to fulfil the strength properties required for this purpose, where a somewhat lower strength concrete is used. The purpose of the core concrete was primarily to achieve the castability of self-compacting concrete whilst incorporating a high content of biochar.

On March 16, 2021, the first carbon negative full-size wall element was cast. The test proved successful regarding the practical execution, the properties of the concrete and the final achieved carbon negativity. Not only did the biochar compensate for the climate gas emissions of the concrete, but also for the reinforcing steel used in the walls.

Photo: Ketil Jacobsen

By both combating a growing waste problem and the world’s increasing CO2 emissions, this solution can change the environmental footprint of a widely used material such as concrete and make it a much-needed planet-positive contribution.

Photo: Ketil Jacobsen