Charred Coffee Grounds Could Make Concrete Up to 30% Stronger, Australian Researchers Find

Every year, the world produces about 10 billion kilograms of coffee waste, roughly 22 billion pounds, and most of it ends up in landfill. Researchers at RMIT University in Australia have found a use for some of it: charred, the grounds can make concrete up to 30 percent stronger.

The obstacle is chemical. Raw organic material such as coffee grounds can't simply be mixed into concrete, because it leaks chemicals that weaken the finished material. So the team heated the waste to over 350 °C (around 660 °F) while depriving it of oxygen, using relatively low energy. This process is called pyrolysis. It breaks down the organic molecules and leaves a porous, carbon-rich charcoal known as biochar, which can bond with the cement matrix and become part of it. The researchers also tried pyrolyzing at 500 °C, but the biochar particles that resulted were not as strong.

Two environmental problems sit behind the work. When the research was first published in 2023, RMIT engineer Rajeev Roychand explained that organic waste in landfill emits large amounts of greenhouse gases, including methane and carbon dioxide. On the other side is construction. Booming global building demand means ever more resource-intensive concrete, and that means ever more sand, typically taken from river beds and banks. Engineer Jie Li said this extraction has a big environmental impact, and that sand supply is hard to sustain because the resource is finite and mining it does damage. A circular-economy approach, she said, could keep organic waste out of landfill while better preserving natural resources like sand.

The idea has moved beyond the lab. In 2024, RMIT and the Macedon Ranges Shire Council poured what was described as a world-first real-world trial: a footpath in Gisborne, Victoria. It included a section made with coffee-biochar concrete, a section using wood-chip biochar, and a standard-concrete control section for comparison.

Later that year, Victoria's Big Build used coffee-biochar concrete for a footpath on the Pakenham Roads Upgrade, the first major infrastructure project to use it. The contractor, BildGroup, estimated the job diverted about 140,000 coffees' worth of grounds from landfill and saved more than 3 metric tons (3.3 US tons) of sand. In early 2025, the RMIT team won the People's Choice Problem Solver Award at Universities Australia's Shaping Australia Awards, and said it was working with a commercialization partner to build a business case for bringing the material to market. The research was published in the Journal of Cleaner Production.

The researchers are candid that the picture is incomplete. They still need to assess the long-term durability of the product, and are testing how the hybrid performs under freeze/thaw cycles, water absorption, abrasion and other stressors. They are also working on biochars from other organic waste, including wood, food and agricultural sources.

Engineer Shannon Kilmartin-Lynch said the research is in its early stages, but that the findings offer an innovative way to greatly reduce the amount of organic waste going to landfill. She said her inspiration, from an Indigenous perspective, involves Caring for Country: ensuring a sustainable life cycle for all materials and avoiding landfill to minimize environmental impact.

What to watch is the durability testing. Strength in the lab and in a few footpaths is one thing; how the material holds up to freezing, water and wear over time will decide whether the business case goes anywhere.