Researchers from The University of Tokyo have developed a new form of concrete that they say could eventually reduce emissions from construction and the built environment.
Calcium carbonate concrete is made from waste concrete and carbon dioxide from the air or industrial exhaust gases.
The university says the concrete shows promise as a future construction material, particularly in places where natural resources are limited.
It is estimated that around 7% of the world’s carbon dioxide emissions come from the manufacture and use of cement, a large proportion of which comes from the use of calcium, which is usually obtained by burning limestone.
Commenting on the development, Professor Ippei Maruyama, from the university, said: “Our concept is to acquire calcium from discarded concrete, which is otherwise going to waste.
“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.”
Calcium carbonate is stable, and therefore makes for a durable construction material, the researchers have claimed.
Further, the ability of the concrete to make use of large quantities of recycled material and waste is a “great benefit”.
However, calcium carbonate concrete cannot currently replace typical concrete.
It is not quite as strong as typical concrete, though for some construction projects, such as small houses, this would not be a problem, the researchers said.
At present, only small blocks a few centimetres in length have been made.
Professor Takafumi Noguchi, from the university, said: “It is exciting to make progress in this area, but there are still many challenges to overcome.
“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.”
Image: Two samples of calcium carbonate concrete, one using hardened cement paste (left) and the other using silica sand. Credit: 2021 Maruyama et al
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