Researchers at the University of Tokyo have turned concrete from a demolished school building and carbon dioxide from the air into bricks.

To make the building blocks, the old concrete was ground down into a powder. In the next step, it was sieved and carbonated over three months. This natural process, in which compounds in concrete react with the CO2 in the air to form calcium carbonate, is usually slow. However, the researchers sped up the process, then pressured the materials in layers in a mould, and finally heated it to form blocks.

Rather than relying on new concrete or bricks, the technique could offer a way to recycle old material while also trapping carbon dioxide in the process. Theoretically, the bricks could be made again and again through the same process.

The new study is based on research from a few years ago, in which CO2 was combined with old concrete. However, back then, only blocks of a few centimetres long could be made.

Photo: I. Maruyama, N.K. Bui, A. Meawad et al.