Coffee grounds an unlikely binder in road base

Coffee ground waste may yet play an unlikely role in the make-up of roads and highways in the distant future.

Swinburne University professor Arul Arulrajah and PhD candidate Teck-Ang Kua have found a way of compressing the organic waste and blending it with an industrial by-product precursor to make a substance that can be used under the road surface.

The duo collected used coffee grounds from cafés around their campus and dried them in a 50°C oven for five days, before using a sieve to filter out any lumps.

They mixed coffee grounds with slag at a ratio of seven to three and added a liquid alkaline solution to bind everything together.

The mixture was compressed into cylindrical blocks, which the researchers say were found to be viable as a stabilised sub-grade material.

Arulrajah, who leads the geotechnical group in the Centre for Sustainable Infrastructure at Swinburne University, has also been investigating the use of recycled materials, such as crushed brick or glass and concrete, for use in road construction.

“I see the baristas throwing away the used coffee grounds,” the avid coffee drinker said. “And I think, ‘why not look at this as an engineering material?’”

It is said the rising worldwide popularity of coffee is creating millions of tonnes per year of spent coffee grounds, usually destined for landfill.

The cafes Arulrajah and Teck-Ang collected from dispose around 150kg of spent beans per week. Arulrajah estimated that Melbourne’s cafés could provide enough base material to build 5km of road per year.

“This would reduce landfill and the demand for virgin quarry materials,” Arulrajah added.

Now that the coffee grounds have been successfully tested in the laboratory, Arulrajah told Quarry that the next phase will be to trial the new sub-grade in the field under traffic conditions and in heat and rain. If that proves successful, then the following phase would be to seek a partner to commercialise the application.

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