Waste concrete used to make new product


Researchers at the University of Tokyo have found a way to combine waste concrete and captured carbon dioxide to create a usable form of concrete called calcium carbonate concrete.

Many Australian companies are already using recycled concrete to supplement crushed rock and aggregate in pavement and road construction projects. Melbourne’s City of Darebin has set a benchmark in the use of recycled materials in the restoration of a local hockey field which included a base layer of recycled concrete and brick.

However, researchers say the new calcium carbonate concrete could also reduce emissions from the construction industry.

It is estimated about 7 per cent of the world’s carbon dioxide emissions come from the manufacture and use of cement, the main component of concrete. A large proportion of the emissions is due to the necessary use of calcium, which is usually obtained by burning limestone.

Inspired by the way some aquatic organisms harden into fossils over time, Professor Ippei Maruyama wondered if the same process that forms hard calcium carbonate deposits from dead organic matter could be applied to concrete. Calcium is essential for the reaction between cement and water to form concrete, and Maruyama saw an opportunity to investigate a less carbon-intensive way of performing the same function.

“Our concept is to acquire calcium from discarded concrete, which is otherwise going to waste,” said 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 research is still in its early stages. While calcium carbonate concrete is a durable construction material it is not as strong as typical concrete so not suitable for all construction projects. Presently, only small blocks of the new product have been made.

Professor Takafumi Noguchi, project manager of Calcium Carbonate Circulation System for Construction, said 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,” Noguchi said.

“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.”

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