Where the Roads Are Paved With Coffee

An Australian engineer with an espresso habit and a love of recycled materials is developing a caffeinated blacktop alternative.
(Photo: Chris Kolbu/Getty Images)
May 15, 2016· 2 MIN READ
Sarah McColl has written for Yahoo Food, Bon Appétit, and other publications. She's based in Brooklyn, New York.

Coffee culture is huge in Melbourne, Australia—so big, in fact, that its flat whites have been imported to American Starbucks’ menus with helpful, explanatory diagrams. But when Arul Arulrajah, a professor of geotechnical engineering at Swinburne University of Technology with a four-to-five-espressos-a-day habit, realized all those coffee grounds were winding up in the trash, his brain started percolating.

“I’m quite passionate about diverting waste from landfills,” he said in an interview with TakePart. “Coffee is quite a big hobby of mine. So is engineering, and so is research, so it was a very fun project to work on.”

This was Arulrajah’s hypothesis: Could all those single-origin-coffee grounds tossed by Melbourne’s cafés be used as a building material? He had studied glass and biosolids—sewage sludge—as road construction material, but coffee grounds would be the first food product he’d worked with. (It was also the first time his research received quite so much media attention, he noted with a laugh.)

Students collected grounds from the local cafés, then dried them in a 120-degree oven. They mixed seven parts coffee grounds with three parts slag, which is a waste product of manufacturing steel. The mixture was bound together with an alkaline solution, compressed into cylindrical blocks, and deemed strong enough to be used as road substrate, according to the team’s recently published study. Next up is seeing how the coffee holds up under traffic simulation in the lab, then testing it at a field site to observe its response to Melbourne’s wet and dry seasons.

“Slowly we’re ticking off the boxes,” Arulrajah said. “Eventually we’ll know how it works, and then it will be ready to go to the next stage.” For now, the project is self-funded, but it reflects what Caroline Baillie, engineering chair at the University of Western Australia, called a growing trend: “Even ordinary companies are starting to develop recycled building materials—it’s not just the crazies anymore,” she told New Scientist.

Typically, the conversation around coffee waste tends toward infamously nonrecyclable K-cups and disposable paper cups—billions of both end up in landfills each year. Discarded coffee cherries, which pollute waterways in coffee-producing countries, present their own problems, but innovators are turning that waste into charcoal and gluten-free flour. But what of the spent grounds? The average coffee shop throws out around 22 pounds of coffee grounds a day. Since 1995, Starbucks has run its free “Grounds for Your Gardens” program, which allows customers to take the waste to use in compost or as a soil additive, and in Melbourne, Arulrajah said, a couple start-ups collect grounds from cafés for compost and worm farming.

Some start-ups are thinking bigger than the lowly worm. London-based Bio-bean collects not from cafés but from wholesale instant coffee manufacturers, whose products, unbelievably, half the world prefers to drink. Bio-bean separates the coffee waste into oil that can power cars and trucks, as well as biomass pellets that can be used in heaters as a carbon-neutral clean fuel. So not only could we be driving on roads made from coffee waste, but our cars could be propelled by it too.

But even in coffee-crazy Australia, coffee grounds can’t compete with more pressing waste products finding their way to the landfills.

“Here in Melbourne, the bigger waste items are construction demolition waste and industrial waste. There’s about 2 million tons of concrete that goes to waste per annum,” Arulrajah said. Coffee, on the other hand, contributes between 50,000 and 100,000 tons in landfill occupancy, he estimated. “So that’s why it still hasn’t reached the capacity to be one of the high-priority areas, but I believe one day it will.”