Extra-strong concrete — with coffee

RMIT University has come up with a novel use for spent coffee grounds — as a valuable component in concrete.

The university is currently collaborating with Macedon Ranges Shire Council on a coffee concrete footpath trial in Gisborne.

RMIT has several other projects planned across Victoria in which coffee grounds will be turned into biochar and transformed into a resource for the construction industry. The RMIT team will partner with Australian-owned BildGroup — a civil infrastructure, asphalt paving and road profiling company — to deliver these circular-economy projects.

Australia generates 75 million kilograms of ground coffee waste every year. Most of this waste currently goes to landfill, but it has the potential to replace up to 655m kg of sand in concrete because spent coffee is a denser material. Globally, 10bn kg of spent coffee is generated annually, which could replace up to 90bn kg of sand in concrete.

The team’s coffee biochar (left) next to spent coffee. Credit: Carelle Mulawa-Richards, RMIT University.

While organic waste like coffee grounds cannot be added directly to concrete because it would decompose over time and weaken the building material, the RMIT team has developed a technique to make a suitable coffee biochar via a low-energy process without oxygen at 350°C. The resulting mixture makes the concrete 30% stronger, the researchers said.

The team is using a similar technique to turn other organic waste, including wood chips, into biochar that can also be used to make stronger concrete. Both types of biochar are being tested in the Macedon Ranges footpath trial.

Council officers and the RMIT research team were present for the pour of the coffee concrete for the footpath trial in Gisborne. Credit: Carelle Mulawa-Richards, RMIT University.

“It’s very exciting to see this world-first trial of our coffee and wood-based biochar in these footpaths collaboration with Macedon Ranges Shire Council,” said Dr Rajeev Roychand, from RMIT’s School of Engineering.

“Sand is getting scarce over time, and this waste can replace up to 15% of the sand in concrete.”

Shane Walden, Council’s Director of Assets and Operations, said it was important for the council to be involved in projects such as this and to be working closely with universities like RMIT.

“This not only helps improve the knowledge level of our contractors and our staff, but it also has lots of other benefits and benefits that are important to our community,” he said.

“This includes helping the environment, acting sustainably and, most importantly, reducing waste to landfill and having a circular economy.”

Walden said that despite the fact that the new concrete contains coffee grounds or mulch, residents aren’t really going to see or smell any difference.

Turning coffee concrete into a commercial reality

If the trial concrete footpaths in Gisborne perform well, the RMIT team is aiming for the commercial rollout of its innovation.

“We are currently working in the supply chain sector so that we can make this research into a mainstream product for commercial applications, and we’re not only looking into coffee ­— we’re expanding this into all forms of different organic waste,” Roychand said.

“Every biochar produced from a different organic material comes with varying composition, in addition to the difference in carbon content, particle size and absorbency, that can boost the performance of concrete in a range of ways.”

If this RMIT innovation can be integrated into the supply chain, it might bring cost savings for construction companies and concreters by reducing the amount of cement needed.

“Since we are achieving a 30% increase in strength for the coffee concrete, this could reduce the required cement content by as much as 10%, based on our previous experience,” Roychand said.

The trial with Macedon Ranges Shire Council did not reduce the amount of cement normally used to make concrete for footpath projects, but the RMIT team plans to experiment with using less cement in future.

‘Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength’ has been published in the Journal of Cleaner Production.

Top image caption: The first pour of the coffee concrete for the footpath trial in Gisborne. Credit: Carelle Mulawa-Richards, RMIT University.