In Summary

  • The rising worldwide popularity of coffee is creating more than millions of tonnes per year of spent coffee grounds, usually destined for landfill.
  • Swinburne engineers are leading the way on recycling this insoluble waste into building materials.

Swinburne University of Technology engineers have turned used coffee grounds into building materials for roads.

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

He is also an avid coffee drinker. “I see the baristas throwing away the used coffee grounds and I think, ‘why not look at this as an engineering material?’” he says.

Professor Arul Arulrajah sitting at axil coffee roasters drinking coffee
Professor Arulrajah having his morning espresso at Axil Coffee Roasters.

Professor Arulrajah and PhD candidate Teck-Ang Kua collected used coffee grounds from cafés surrounding Swinburne’s Hawthorn campus. They dried them in a 50°C oven for five days, then sieved the grounds to filter out lumps.

They then mixed seven parts coffee grounds with three parts of slag – a waste product from steel manufacturing. A liquid alkaline solution was added to bind everything together.

The mixture was compressed into cylindrical blocks that proved strong enough to use as the subgrade material that sits under a road surface.

“On average the cafés we collect from dispose of about 150 kg of coffee grounds per week," says Professor Arulrajah.

“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."

This research is a collaboration with Suranaree University of Technology, Thailand; Southeast University, Nanjing, China; and Shanghai Jiao Tong University, China. It has been published in Construction and Building Materials.