University adds coffee grounds to asphalt mix

Professor Arul Arulrajah, who leads the geotechnical group in the Center 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.
 

Arulrajah and PhD candidate Teck-Ang Kua collected used coffee grounds from cafés surrounding Swinburne’s Hawthorn campus in Victoria, Australia. They dried them in a 50 degree Celsius 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 330 pounds (150 kilograms) of coffee grounds per week," says Arulrajah. “We estimate that the coffee grounds from Melbourne’s cafés could be used to build three miles (five kilometers) 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 the journal Construction and Building Materials.