Australian researchers turn morning coffee waste into greener concrete

That's the promise of an Australian university turning used coffee grounds into a material that can be added to concrete to make it stronger and more sustainable, potentially lowering greenhouse gas emissions.

Concrete production, which involves mixing sand and gravel with cement and water, is a major producer of greenhouse gases, responsible for around 7% of the world's emissions, according to the United Nations.

Researchers at Melbourne's RMIT University heated coffee waste without oxygen, a process known as pyrolysis, to create a substance called biochar that can replace up to 15% of the sand used in concrete.

The inclusion of the biochar makes the concrete 30% stronger and reduces the amount of cement needed by up to 10%, said lead researcher Rajeev Roychand.

"This ticks all the boxes," he said. "You preserve carbon and you are getting significantly higher strength."

Roughly 50 billion metric tons of sand is dug up each year, mostly for use in concrete, a 2022 U.N. report said. Its extraction is often environmentally destructive and it is in increasingly short supply, the report said.

Cement production, which involves heating a mixture of limestone and clay to around 1,500  degrees Celsius (2,732°F), is responsible for most of concrete's emissions.

The Macedon Ranges Shire Council near Melbourne used the coffee concrete earlier last month to construct a footpath.

RMIT is talking with several construction firms and concrete makers and with Starbucks to take its waste coffee grounds, and could form a company to make biochar, Roychand said. Starbucks did not respond to a request for comment.

Australian infrastructure company Bild Group said it planned to trial the concrete and hoped to use it on major road projects. Construction giant Arup supported the research.

Millions of tons of used coffee grounds are produced globally and most are sent to landfills where they emit methane as they break down.

Australia generates around 75,000 tons of waste coffee grounds a year and biochar made from this could replace up to 655,000 tons of sand in concrete because it is a denser material, Roychand said. Globally, coffee-waste biochar could replace up to 90 million tons of sand in concrete, he said.

Food waste accounts for around 3% of Australia's emissions, according to the government, and most could eventually be made into biochar, Roychand said.

"We anticipate that about 60-70% (of organic waste) we can divert from landfill into concrete applications," he said.

Other international universities are also researching the potential of biochar and other bio-engineering in concrete. RMIT was the first to use waste coffee grounds in this way, Roychand said.