Using spent coffee grounds for making concrete can greatly boost circularity

9 Januari 2024

Photo: Pexels/Caio

Spent coffee grounds are no longer any use for making coffee, but they can still be of great use in other ways. They can be reused to pave roads and one day they could help prevent neurodegenerative diseases, for example.

But there is more. Engineers in Australia have devised a technique for making concrete nearly 30% stronger by mixing it with waste coffee grounds turned into biochar through a low-energy process called pyrolysis, which involves heating organic waste in the absence of oxygen.

“The concrete industry has the potential to contribute significantly to increasing the recycling rate of this waste material. However, due to its high organic content, it is unsuitable to be used directly in structural concrete,” the scientists explain in their study.

Pyrolysing spent coffee grounds at 350°C, however, led to “a significant improvement in its material properties, which resulted in a 29.3% enhancement in the compressive strength of the composite concrete blended with coffee biochar,” they report.

Coffee biochar is used in the new method to replace a portion of the sand for making concrete. If scaled up, this technique could have a positive environmental impact by reducing the volume of natural sand used in construction projects, which currently stands at 50 billion tonnes globally every year.

“The ongoing extraction of natural sand around the world – typically taken from river beds and banks – to meet the rapidly growing demands of the construction industry has a big impact on the environment,” notes Professor Jie Li, who led the research.

“There are critical and long-lasting challenges in maintaining a sustainable supply of sand due to the finite nature of resources and the environmental impacts of sand mining,” Li adds. “With a circular-economy approach, we could keep organic waste out of landfill and also better preserve our natural resources like sand.”

Thus, replacing sand with biochar from spent coffee grounds could not only strengthen concrete but also help the environment and reduce waste at the same time. Each year 10 billion kilograms of coffee grounds are generated. Australia alone produces 75 million kilograms of that. Most of this organic waste ends up in landfills.

The research is still in its early stages, “but these exciting findings offer an innovative way to greatly reduce the amount of organic waste that goes to landfill,” stresses Shannon Kilmartin-Lynch, a postdoctoral research fellow at RMIT University in Melbourne.

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