Somewhere in the long human habit of building, we keep discovering that what we discard can become the foundation of what we make. In Australia, researchers at RMIT took the bitter residue of the world's morning coffee, charred it without oxygen into a porous charcoal, and mixed it into concrete, where it appears to make the mixture up to 30 percent stronger. The work moved from laboratory to footpath in Gisborne, Victoria, and then onto a larger infrastructure project, quietly easing two pressures at once: the landfill that swallows organic waste and the riverbeds that have long supplied natu
Charred Coffee Grounds Could Make Concrete Up to 30% Stronger, and Are Already Going Into Real Footpaths
Coffee grounds can't go straight in. First, they have to be charred.
Mark
Why does charring the coffee matter? Why not just mix the grounds in?
Mimi
Raw grounds leak chemicals that weaken concrete. Heating them above 350 °C without oxygen turns them into porous biochar, which bonds into the cement instead of fighting it.
Mark
And the 30 percent figure, what does it mean for a footpath?
Luke
Careful there. It's up to 30 percent, a best-case result from the research. The reporting doesn't say what mix or conditions produced it, or whether the footpaths reached it.
Mimi
Fair. What the footpaths show is that it can be poured and used outside a lab.
Mark
What did those trials include?
Mimi
Gisborne had three sections: coffee biochar, wood-chip biochar, and plain concrete as a control. Then Pakenham, where BildGroup estimated about 140,000 coffees' worth of grounds diverted and over 3 tons of sand saved.
Luke
Note that's the contractor's estimate. And nothing reported here says how the footpaths have performed over time.
Mark
Is that the main open question?
Luke
Yes. Freeze/thaw, water absorption and abrasion testing is still underway. Durability is unproven.
Mimi
The 500 °C result is a useful detail too. Hotter wasn't better; those particles were weaker.
Mark
What comes next?
Mimi
Other waste sources for biochar, and a commercialization partner building a business case.
The Pulse
- Roughly ten billion kilograms of coffee waste a year is heading to landfill, where it releases greenhouse gases.
- Demand for concrete keeps climbing, and the natural sand it relies on is being dug from riverbeds faster than it can be replaced.
- RMIT engineers heat coffee grounds above 350 °C without oxygen, turning them into biochar that bonds with cement and lifts strength by up to 30 percent.
- The material has already moved from a Gisborne footpath trial to the Pakenham Roads Upgrade, diverting about 140,000 coffees' worth of grounds and saving over 3 tons of sand.
- Freeze/thaw, water absorption and abrasion tests are still underway, and a commercialization partner is building the business case that will decide its market future.
Somewhere in the long human habit of building, we keep discovering that what we discard can become the foundation of what we make. In Australia, researchers at RMIT took the bitter residue of the world's morning coffee, charred it without oxygen into a porous charcoal, and mixed it into concrete, where it appears to make the mixture up to 30 percent stronger. The work moved from laboratory to footpath in Gisborne, Victoria, and then onto a larger infrastructure project, quietly easing two pressures at once: the landfill that swallows organic waste and the riverbeds that have long supplied natural sand. Whether this humble hybrid endures under frost, water and wear remains an open question, and the answer will shape whether it stays a curiosity or becomes an ordinary part of how we build.
In 2024, a footpath in Gisborne, Victoria, became the first real-world test of concrete strengthened with charred coffee grounds. RMIT University and the Macedon Ranges Shire Council poured three side-by-side sections: one with coffee biochar, one with wood-chip biochar, and one standard concrete as the control.
The idea grew from RMIT engineers who found that coffee grounds, treated correctly, can make concrete up to 30 percent stronger. Each year the world produces about 10 billion kilograms of coffee waste, most of it bound for landfill, where organic matter releases methane and carbon dioxide. At the same time, concrete demand keeps rising, and the natural sand that goes into it is mined from riverbeds in a way that is finite and damaging. Engineer Jie Li argued that a circular approach could keep organic waste out of landfill while sparing natural resources.
Raw grounds cannot simply be stirred in, because they leach chemicals that weaken concrete. The team pyrolyzed the waste above 350 °C with oxygen excluded, producing a porous, carbon-rich biochar that bonds into the cement. At 500 °C the particles came out weaker, so the lower temperature proved better.
Later in 2024 the material reached a larger job: a footpath on Victoria's Pakenham Roads Upgrade, the first major infrastructure project to use it. Contractor BildGroup estimated the work diverted about 140,000 coffees' worth of grounds and saved more than 3 metric tons of sand.
The researchers remain candid that the story is unfinished. Long-term durability, freeze/thaw cycles, water absorption and abrasion are still being tested, and biochars from wood, food and agricultural waste are under study. Shannon Kilmartin-Lynch, drawing on the Indigenous idea of Caring for Country, described the work as a way to keep materials in a sustainable life cycle. In early 2025 the team won the People's Choice Problem Solver Award at the Shaping Australia Awards, and it is now building a business case with a commercialization partner. Those durability results and that business case will decide whether coffee concrete stays a footpath curiosity or goes further.
In 2024, a stretch of footpath in Gisborne, Victoria, became the first real-world test of an unlikely building material: concrete strengthened with charred coffee grounds. RMIT University and the Macedon Ranges Shire Council poured it in three sections side by side. One used coffee biochar concrete, one used biochar made from wood chips, and one was standard concrete, there to serve as the control.
The idea behind it came from RMIT engineers in Australia, who found that coffee grounds treated the right way can make concrete up to 30 percent stronger. The world produces about 10 billion kilograms (22 billion pounds) of coffee waste a year, and most of it ends up in landfill. Rajeev Roychand, an RMIT engineer, noted when the work was first published in 2023 that organic waste in landfill emits large amounts of greenhouse gases, including methane and carbon dioxide.
Concrete has its own problem. Global construction keeps growing, and so does demand for the resource-intensive material. Natural sand, typically taken from river beds and banks, is a major ingredient. RMIT engineer Jie Li said the continuing extraction of sand to meet that demand has a big environmental impact, and that sand supply is difficult to sustain because the resource is finite and mining it does damage. A circular-economy approach, in her view, could keep organic waste out of landfill while preserving natural resources like sand.
The grounds can't simply be stirred into a mix. Raw organic material leaches chemicals that weaken concrete. So the team heated the coffee waste to over 350 °C (around 660 °F) with oxygen kept out, a process called pyrolysis, using relatively little energy. 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. Roychand and colleagues also tried pyrolysis at 500 °C, but the biochar particles that resulted were not as strong.
After the Gisborne trial, the material moved onto a larger job. Later in 2024, 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 that the work diverted roughly 140,000 coffees' worth of grounds from landfill and saved more than 3 metric tons (3.3 US tons) of sand.
The researchers are candid that the picture is incomplete. They still need to assess the long-term durability of the product, and they are testing how the coffee-cement hybrid handles freeze/thaw cycles, water absorption, abrasion and other stresses. They are also working on biochars from other organic waste, including wood, food and agricultural sources. Shannon Kilmartin-Lynch, another RMIT engineer, said the research is at an early stage but offers a way to greatly reduce the organic waste going to landfill. She added that her inspiration comes from an Indigenous perspective of Caring for Country: a sustainable life cycle for all materials, and keeping things out of landfill.
In early 2025, the team won the People's Choice Problem Solver Award at Universities Australia's Shaping Australia Awards. They said they were working with a commercialization partner to build a business case for bringing the material to market. The durability results, and that business case, will decide whether coffee concrete stays a footpath curiosity or goes further.
Notable Quotes
Our research is in the early stages, but these findings offer an innovative way to greatly reduce the amount of organic waste that goes to landfill.— Shannon Kilmartin-Lynch, RMIT engineer
With a circular-economy approach, we could keep organic waste out of landfill and also better preserve natural resources like sand.— Jie Li, RMIT engineer
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