Researchers at Swinburne University of Technology may have provided coffee connoisseurs with another reason to keep drinking, developing a novel method that turns coffee grounds into building materials for roads.

Professor Arul Arulrajah, who leads the geotechnical group in the Centre for Sustainable Infrastructure at Swinburne, said he got the idea to test coffee grounds after observing baristas.

“I see the baristas throwing away the used coffee grounds and I think, ‘Why not look at this as an engineering material?’” he said.

Professor Arulrajah and PhD candidate Teck-Ang Kua collected used coffee grounds from cafés surrounding Swinburne’s Hawthorn campus and dried them in a 50°C oven for five days. They then mixed seven parts coffee grounds with three parts of slag – a waste product from steel manufacturing. A liquid alkaline solution was added as a binding agent.

The resultant material proved strong enough to use as the subgrade material that sits under a road surface.

The researchers think the findings, published in Construction and Building Materials, could have huge implications for the development of more sustainable roads, putting a dent in the millions of tonnes of used coffee grounds that make their way to landfills across the globe every year.

“On average the cafés we collect from dispose of about 150 kilograms of coffee grounds per week,” Professor Arulrajah said.

“We estimate that the coffee grounds from Melbourne’s cafés could be used to build five kilometres of road per year. This would reduce landfill and the demand for virgin quarry materials.”

The research was in collaboration with Suranaree University of Technology, Thailand; Southeast University, Nanjing, China; and Shanghai Jiao Tong University, China.

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