Every day, enormous quantities of spent coffee travel toward landfill, where they quietly release gases that warm the planet, while the construction world keeps digging up river sand faster than it can be replaced. In Australia, researchers at RMIT University have found a way to let these two problems meet: by cooking coffee grounds into a porous charcoal and folding it into concrete, they report a material about 30 percent stronger. The finding is promising but young, standing at the threshold between a laboratory result and a building material that must endure years of weather and wear befor
Charred Coffee Grounds Could Make Concrete 30 Percent Stronger, Australian Researchers Find
Cook the grounds first, and the concrete gets stronger.
Mark
Start with the basic trick. Why can't you just put coffee grounds in concrete?
Mimi
Because raw organic material leaks chemicals that weaken it. The team heats the grounds above 350 degrees Celsius without oxygen, which turns them into biochar, a porous charcoal that bonds into the cement matrix.
Mark
And that's where the 30 percent comes from?
Mimi
That's the reported strength gain, yes. It's the headline result of the research.
Luke
I'd keep the word reported in front of it. The piece gives us the figure but not the test conditions, the mix proportions, or what it's measured against. Thirty percent stronger in what sense, I can't tell you from this.
Mark
Fair. What about the temperature detail?
Mimi
They also tried 500 degrees, and the biochar particles came out weaker. So hotter wasn't better, and the lower setting also uses less energy.
Mark
Why does the sand come into it?
Mimi
Concrete needs sand, and natural sand is dredged from river beds and banks. Jie Li says that extraction damages the environment and the supply is finite. Biochar is meant to ease that pressure.
Luke
Careful, though. The article doesn't say how much sand the biochar would actually replace, or at what scale. The sand benefit is the stated motivation, not a measured outcome.
Mark
And what's still unknown?
Mimi
Durability. They're testing freeze/thaw cycles, water absorption and abrasion. Until those results are in, nobody knows if it lasts as long as ordinary concrete.
Luke
Right, and that's the question that decides whether this becomes a building material or stays a lab result.
Der Puls
- Raw coffee grounds weaken concrete, so a simple idea of mixing waste into building material fails at the start.
- Roughly 10 billion kilograms of coffee waste a year decay in landfills, releasing methane and carbon dioxide.
- RMIT engineers heat the grounds above 350 degrees Celsius without oxygen, turning them into biochar that bonds with cement.
- The lab result shows about 30 percent added strength, but freeze-thaw, water and abrasion tests must still prove it lasts.
- The team is extending the method to wood, food and agricultural waste, with durability results now the decisive next step.
Every day, enormous quantities of spent coffee travel toward landfill, where they quietly release gases that warm the planet, while the construction world keeps digging up river sand faster than it can be replaced. In Australia, researchers at RMIT University have found a way to let these two problems meet: by cooking coffee grounds into a porous charcoal and folding it into concrete, they report a material about 30 percent stronger. The finding is promising but young, standing at the threshold between a laboratory result and a building material that must endure years of weather and wear before it can be trusted.
Raw coffee grounds cannot simply be stirred into concrete. Left untreated, they leak chemicals that weaken the material. So engineers at RMIT University in Australia tried a different path: they cooked the grounds first, and the result, they report, is concrete about 30 percent stronger.
The method is pyrolysis. The team heated spent coffee above 350 degrees Celsius with oxygen kept away, breaking down its organic molecules into a porous, carbon-rich charcoal called biochar. Unlike the raw grounds, this biochar can bond with the cement and become part of it. The process runs at relatively low energy. Temperature proved decisive: grounds cooked at 500 degrees produced weaker particles than those cooked at the lower setting.
The work addresses two pressures at once. The world produces about 10 billion kilograms of coffee waste a year, and most of it ends up in landfill, where it gives off methane and carbon dioxide. Meanwhile, the booming construction industry relies on river sand, a finite resource whose extraction does its own environmental damage. Engineer Jie Li argues that a circular approach could keep organic waste out of landfill while sparing natural sand.
The researchers are candid about their position. A strong lab result is not proof that a building material will last, so the team is now testing how the hybrid holds up under freeze-thaw cycles, water absorption and abrasion. Colleague Shannon Kilmartin-Lynch calls the work early-stage but important, and says his inspiration draws on the Indigenous idea of Caring for Country: keeping materials in a sustainable life cycle and out of landfill. The findings, published in the Journal of Cleaner Production, now wait on the durability tests and on whether wood and food waste can match the coffee.
Raw coffee grounds can't simply be stirred into concrete. Left as they are, they leak chemicals that weaken the material. So engineers at RMIT University in Australia took a different route: they cooked the grounds first, and the result, they report, is concrete about 30 percent stronger.
The method is pyrolysis. The team heated spent coffee to more than 350 degrees Celsius, around 660 Fahrenheit, while keeping oxygen away from it. The heat breaks down the organic molecules and leaves behind a porous, carbon-rich charcoal called biochar. That biochar can form bonds with the cement matrix and become part of it, which the raw grounds cannot. The process runs at relatively low energy levels, the researchers note.
Temperature mattered. Rajeev Roychand and his colleagues also tried pyrolyzing the grounds at 500 degrees Celsius, but the biochar particles that came out were not as strong as those made at the lower temperature.
The work targets two problems at once. The world produces about 10 billion kilograms of coffee waste a year, roughly 22 billion pounds, and most of it ends up in landfill. Roychand explained that organic waste there gives off large amounts of greenhouse gases, including methane and carbon dioxide, which contribute to climate change.
The second problem is sand. A booming global construction industry keeps raising demand for resource-intensive concrete, and natural sand, typically taken from river beds and banks, is a key ingredient. RMIT engineer Jie Li said that this ongoing extraction has a big environmental impact. Sand supply is finite, he said, and sand mining carries its own damage. With a circular-economy approach, he argued, organic waste could stay out of landfill while natural resources like sand are better preserved.
The researchers are candid about how far along they are. They still need to assess the long-term durability of the coffee-cement product. Testing is under way on how the hybrid material holds up under freeze/thaw cycles, water absorption, abrasion and a range of other stresses. A strong result in the lab is not the same as proof that a building material will last.
The team is also looking past coffee. They are working on making biochar from other organic waste, including wood, food waste and agricultural waste. Shannon Kilmartin-Lynch, another RMIT engineer, described the research as early-stage but said the findings offer an innovative way to greatly reduce the organic waste going to landfill. He added that his inspiration comes from an Indigenous perspective of Caring for Country: ensuring a sustainable life cycle for all materials and keeping things out of landfill to limit environmental impact.
The research was published in the Journal of Cleaner Production. The article was first published in September 2023. What to watch now is the durability testing, which will show whether the 30 percent gain survives real-world conditions, and whether biochar from wood and food waste performs as well as the coffee version.
Bemerkenswerte Zitate
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
Extraction of natural sand for construction has a big impact on the environment, and a circular-economy approach could keep organic waste out of landfill while preserving resources like sand.— Jie Li, RMIT engineer (paraphrased)
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