Charred Coffee Grounds Could Make Concrete Up to 30 Percent Stronger

Used coffee grounds, usually thrown away, could help build stronger concrete. Engineers at RMIT University in Australia found that adding charred coffee grounds can make concrete up to 30 percent stronger, ScienceAlert reported.

The idea targets two problems at once: the huge volume of coffee waste that ends up in landfills, and the heavy environmental cost of the sand that concrete depends on.

Why raw coffee grounds do not work, and what the team did instead

According to ScienceAlert, the world produces about 10 billion kilograms (22 billion pounds) of coffee waste each year, and most of it is sent to landfills. RMIT engineer Rajeev Roychand said that organic waste releases large amounts of greenhouse gases, including methane and carbon dioxide.

Concrete has its own footprint. RMIT engineer Jie Li said that taking natural sand from river beds and banks to feed the construction industry has a major environmental impact, and that sand is a finite resource. He argued that a circular-economy approach could keep organic waste out of landfills while protecting natural resources.

Raw coffee grounds cannot simply be stirred into concrete, because they leak chemicals that weaken it. So the researchers heated the waste to over 350 °C (around 660 °F) with no oxygen present, a process called pyrolysis. This turns the grounds into biochar, a porous, carbon-rich charcoal that can bond with the cement mixture and become part of it.

The team also tried heating the grounds to 500 °C, but the biochar particles that resulted were not as strong.

How the project has developed

• 2023: The research was first published in the Journal of Cleaner Production.
• 2024: RMIT and the Macedon Ranges Shire Council poured what ScienceAlert called a world-first real-world trial: a footpath in Gisborne, Victoria, built with coffee biochar concrete. It was laid next to a section made with wood-chip biochar and a section of standard concrete used for comparison.
• Later in 2024: Victoria's Big Build used the material for a footpath on the Pakenham Roads Upgrade, described as the first major infrastructure project to use it. Contractor BildGroup estimated that the job kept the grounds from roughly 140,000 coffees out of landfill and saved more than 3 metric tons (3.3 US tons) of sand.
• Early 2025: The 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 on a business case to bring the material to market.

Why it matters

If the approach proves itself, everyday waste from cafes and kitchens could become an ingredient in footpaths and other concrete structures, while reducing the demand for mined sand. Footpaths in Victoria already show the material can be used outside a laboratory.

The researchers are cautious, though. They said they still need to assess the long-term durability of the product. ScienceAlert reported that they are now testing how the coffee-cement mix performs under freeze-thaw cycles, water absorption, abrasion and other stresses.

RMIT engineer Shannon Kilmartin-Lynch said the research is still at an early stage, but called the findings an innovative way to greatly cut the organic waste going to landfill.

What happens next

The team is also working on making biochar from other organic waste, including wood, food and agricultural waste, according to ScienceAlert. Alongside the durability tests, a commercial partner is helping to build the business case for selling the material.

Around Prague, based on reporting by ScienceAlert