Coffee grounds can be turned into building materials for roads

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 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 150kg 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."