Somewhere between the morning cup and the rubbish bin, a quiet question has been put to the coffee grounds most of us never think twice about: could they become part of the structure that holds our cities up? Researchers at RMIT University in Australia have answered with a tentative yes, charring the spent grounds into biochar and folding them into cement, where they appear to lend concrete about 30 percent more strength. It is an early finding, offered at a moment when the world's appetite for concrete and for sand is pressing hard against the limits of both, and when the waste that most of u
Charred Coffee Grounds Could Make Concrete 30% Stronger, RMIT Researchers Find
Char them, mix them into concrete, and the result can be about 30 percent stronger.
Mark
So what actually did the team do with the coffee?
Mimi
They heated used grounds above 350 °C with no oxygen, which turns them into biochar, a porous carbon-rich charcoal. That material bonds into the cement, and the reported result is concrete about 30 percent stronger.
Mark
Why not just add the grounds directly?
Mimi
Raw organic material leaks chemicals that weaken concrete. The charring step is what makes it usable.
Luke
Before we get excited, that 30 percent figure comes from the researchers' own work. The article doesn't say what kind of concrete or what strength test it refers to.
Mimi
Fair. And they say themselves it's early stage. Durability is still unassessed.
Mark
What are they testing next?
Mimi
Freeze/thaw cycles, water absorption, abrasion and other stresses. Concrete has to last decades, so those results matter a lot.
Luke
Also, the article doesn't say how much sand this could actually replace, or what it would cost at scale. The sand benefit is a stated hope, not a measured outcome.
Mark
And the temperature detail?
Mimi
They tried 500 °C too, and the biochar particles came out weaker. So the recipe is sensitive to how it's made.
Luke
Right, and the other waste sources, like wood and food scraps, are only being worked on. Nothing reported there yet.
Le Pouls
- Roughly 10 billion kilograms of coffee waste pile up each year, and most of it rots in landfill, quietly releasing methane and carbon dioxide.
- Global construction keeps drawing on natural sand from riverbeds and banks, and the finite supply is being stripped faster than it can recover.
- Raw coffee grounds cannot simply be mixed into cement, because their organic compounds leach out and weaken the concrete from within.
- The team heats the grounds above 350 °C without oxygen to produce biochar, and at 500 °C the particles lose the strength that made them useful.
- Early results suggest roughly 30 percent greater strength, but durability under freeze-thaw cycles, water absorption and abrasion is still being tested.
- The approach may spread to wood, food and agricultural waste, though it remains a laboratory promise until the wear tests come back.
Somewhere between the morning cup and the rubbish bin, a quiet question has been put to the coffee grounds most of us never think twice about: could they become part of the structure that holds our cities up? Researchers at RMIT University in Australia have answered with a tentative yes, charring the spent grounds into biochar and folding them into cement, where they appear to lend concrete about 30 percent more strength. It is an early finding, offered at a moment when the world's appetite for concrete and for sand is pressing hard against the limits of both, and when the waste that most of us discard continues to release greenhouse gases in landfill. The work reminds us that what we throw away is sometimes only material waiting for a second purpose.
At RMIT University in Australia, a team of researchers has found a way to give coffee grounds a second life. Rather than sending them to landfill, they char the grounds and mix the result into concrete, and the early findings suggest the material can be about 30 percent stronger. It is a small discovery with large implications, touching two problems that rarely get solved together.
The first problem is the waste. Around 10 billion kilograms of coffee grounds are produced each year, and most end up in landfill, where organic material releases methane and carbon dioxide. RMIT engineer Rajeev Roychand has pointed out that this slow release of greenhouse gases is a hidden cost of our daily habits.
The second problem is concrete itself. The booming construction industry relies heavily on natural sand, usually dredged from rivers and riverbanks, and engineer Jie Li warns that this extraction takes a heavy toll on the environment and on a resource that is not endless. Her hope is a circular approach, in which waste becomes material rather than refuse.
The challenge lies in preparation. Raw grounds would leach compounds that weaken concrete, so the team heats them to above 350 °C without oxygen, a process called pyrolysis, which produces a porous charcoal that bonds with cement. Temperature proved decisive: at 500 °C the resulting particles were weaker.
The researchers are candid that much is still unknown. They are testing how the material endures freezing and thawing, water and abrasion, and they are exploring similar biochars from wood, food and farm waste. Shannon Kilmartin-Lynch calls the work early-stage but exciting, and frames it through the Indigenous idea of Caring for Country, a commitment to sustainable life cycles for all materials.
The study appears in the Journal of Cleaner Production. Whether the strength gain survives freezing, water and wear will determine how far this idea travels beyond the laboratory.
Researchers at RMIT University in Australia have found a use for the coffee grounds most of us throw away: char them, mix them into concrete, and the result can be about 30 percent stronger. The finding is an early one, but it speaks to two environmental problems at once.
The first is the waste itself. The world generates roughly 10 billion kilograms of coffee waste a year, about 22 billion pounds, and most of it ends up in landfill. RMIT engineer Rajeev Roychand explained, when the work was first published in 2023, that organic waste in landfill releases large amounts of greenhouse gases, including methane and carbon dioxide.
The second problem is concrete. A booming global construction market keeps raising demand for it, and that demand leans on natural sand, typically pulled from river beds and banks. RMIT engineer Jie Li said this extraction has a big environmental impact. She pointed to the finite nature of sand and the damage done by sand mining, and argued that a circular-economy approach could keep organic waste out of landfill while better preserving resources like sand.
The difficulty is that raw coffee grounds cannot simply be stirred into the mix. Organic material leaches chemicals that weaken concrete. So the team treated the waste first, heating it to above 350 °C (around 660 °F) while depriving it of oxygen, using relatively low energy levels. This process, called pyrolysis, breaks down the organic molecules and leaves a porous, carbon-rich charcoal known as biochar. That biochar can bond with the cement matrix and become part of it.
Temperature mattered. Roychand and colleagues also tried pyrolyzing the grounds at 500 °C, but the biochar particles that resulted were not as strong as those made at the lower temperature.
The researchers are candid about what remains unknown. They still need to assess the long-term durability of the coffee-based cement. They are now testing how the hybrid material holds up under freeze/thaw cycles, water absorption, abrasion and a range of other stresses. They are also working on biochars from other organic waste, including wood, food waste and agricultural waste.
RMIT engineer Shannon Kilmartin-Lynch described the work as early-stage, while calling the findings exciting as a way to greatly reduce the organic waste going to landfill. She also described her inspiration from an Indigenous perspective as Caring for Country: ensuring a sustainable life cycle for all materials and avoiding things going into landfill to minimize environmental impact.
The research was published in the Journal of Cleaner Production. ScienceAlert's article is an updated version of one first published in September 2023. The thing to watch is the durability testing: whether the strength gain holds up against freezing, water and wear will decide how far this goes beyond the lab.
Citations marquantes
Our research is in the early stages, but these exciting 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 (paraphrased)
Envie de l'histoire complète ?
Lire l'original sur ScienceAlert ↗
Climate & Environment