Coffee waste reduces the environmental impact of concrete

Research into using waste coffee grounds to strengthen concrete is under way at Melbourne’s RMIT University.

Rajeev Roychand, third from right, with council officers and the RMIT research team at the pour of coffee concrete for a footpath trial in Gisborne

Research into using waste coffee grounds to strengthen concrete is under way at Melbourne’s RMIT University.

The coffee grounds waste increases concrete’s ability to withstand loads by 30 per cent, reduces its impact on the environment and prolongs its lifespan, say structural and materials engineer Rajeev Roychand and his colleagues from the university’s school of engineering.

They found that pyrolyzing the waste coffee, heating the grounds to 350C in a closed chamber, produces material that can replace some of the sand used in concrete.

“In simple terms, it’s re-roasting of the same coffee,” Roychand says. “We roast coffee to bring out aroma and taste: this is the same process, but in the absence of oxygen.”

Pores in the pyrolyzed coffee grounds retain water, which is then slowly released into the surrounding concrete matrix, making the finished product stronger and more durable than ordinary concrete.

RMIT University has used coffee grounds in BildGroup constructions.

Australia produces 75,000 tonnes of waste coffee grounds annually. Some of this coffee waste winds up in landfills, producing greenhouse gas emissions. Using the coffee waste to replace building sand – a limited resource – has multiple environmental benefits.

Roychand estimates concrete made with coffee grounds can deliver the same strength as standard concrete with 10 per cent less material. Portland cement, the key constituent of concrete, is responsible for about 8 per cent of the world’s greenhouse gas production.

The waste coffee grounds heating process adds to the environmental cost of the coffee- grounds biochar, but it is more than offset by the green advantages, Roychand says.

RMIT has run field trials of the coffee concrete in footpaths, one with the Macedon Ranges Shire Council and a second with construction company BildGroup. The performance of the concrete was “extremely good” in the first Macedon Ranges field trial, Roychand says.

Victoria’s Transport Department is conducting further tests on the coffee concrete’s strength and durability, and once transport department officials are

satisfied, Roychand expects to see coffee concrete used in larger road projects. Even so, the cost of collecting and processing the coffee grounds waste is still a barrier.

Roychand and RMIT are planning a pilot-scale coffee biochar production facility and he believes that over time, coffee- grounds biochar can be competitive at scale.

“In the beginning, it will be at a premium cost, but down the line when it’s accepted in the market and you have a bigger infrastructure to produce at a mass scale, the price will come down,” he says.

The coffee biochar production system is now in the process of being patented, and negotiations are in the advanced stages of granting a commercialisation partner an exclusive licence.

The RMIT team is now looking beyond coffee grounds to the millions of tonnes of organic waste generated by Australians every year.

“We want to set up the first entity here in Australia, showcase and then slowly expand, depending on how it performs,” Roychand says. “And we are not keeping it to coffee: the larger focus is to divert all biodegradable, organic waste which ends up in landfills.”