Two concrete samples on white background

A concrete solution to carbon capture

A newly developed concrete – made from recycled construction waste and industrial exhaust gases – could reduce construction emissions, suggests a study published in Journal of Advanced Concrete Technology.

This shows promise for a cleaner construction future when natural resources are limited.

The concrete industry is enormous – so large, in fact, that an estimated 7% of the world’s carbon dioxide emissions come from manufacturing and using concrete.

Most of these emissions come from burning limestone to collect calcium, which is critical to the concrete-forming chemical reaction between water and cement

Now, researchers, led by Ippei Maruyama and Takafumi Noguchi of the University of Tokyo, have found a way to repurpose waste concrete and make a new form called calcium carbonate concrete.

Read more: Chemistry, concrete and ceramic cement

“Our concept is to acquire calcium from discarded concrete, which is otherwise going to waste,” says Maruyama. “We combine this with carbon dioxide from industrial exhaust or even from the air. And we do this at much lower temperatures than those used to extract calcium from limestone at present.”

The researchers were inspired by the way some aquatic animals harden into fossils over time. They wondered whether the same process that turns dead animals into hard calcium carbonate deposits could be applied to waste concrete, instead of using traditional curing methods.

While the new concrete is pretty tough, it isn’t quite ready to be used in place of traditional concrete – although it may be suitable for use on small projects, like houses.

“It is exciting to make progress in this area, but there are still many challenges to overcome,” says Noguchi.

“As well as increasing the strength and size limits of calcium carbonate concrete, it would be even better if we could further reduce the energy use of the production process.

“However, we hope that in the coming decades, carbon-neutral calcium carbonate concrete will become the mainstream type of concrete and will be one of the solutions to climate change.”