Coffee concrete trial turns organic waste into a valuable resource

RMIT researchers collaborated with Macedon Ranges Shire Council to conduct a world-first coffee concrete footpath trial.

SDGs

Key points

RMIT and Macedon Ranges Shire Council partnered for the world's first coffee concrete footpath trial, transforming organic waste into sustainable construction materials.
Converting spent coffee grounds into biochar reduces greenhouse gas emissions and lessens reliance on scarce resources like sand in concrete production.
Enhancing concrete strength by 30% with biochar additives offers cost savings, supports sustainability, and promotes wider adoption in construction, fostering a circular economy.

The research study

Organic waste going to landfill, including spent coffee grounds, contributes 3% of greenhouse gas emissions, but Dr Rajeev Roychand and his colleagues at RMIT are set on transforming this waste into a valuable resource for the construction industry.

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

Organic waste cannot be added directly to concrete because it would decompose over time and weaken the building material. To overcome this challenge, the team has developed a technique to make concrete 30% stronger by using coffee biochar made with a low-energy process without oxygen at 350 degrees Celsius, to give the drink-additive a “double shot” at life and reduce waste going to landfill.

They use a similar technique to turn other organic waste, including wood chips, into biochar that can also be used to make stronger concrete.

Australia generates 75 million kilograms of ground coffee waste every year – most of it goes to landfills, but it could replace up to 655 million kilograms of sand in concrete because it is a denser material. Globally, 10 billion kilograms of spent coffee is generated annually, which could replace up to 90 billion kilograms of sand in concrete.

Roychand said coffee and wood-chip biochar can replace a portion of the river sand that was used to make concrete, and the team was collaborating with the council to trial both types of biochar in concrete footpaths in Gisborne.

“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 Roychand from the 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, was pleased to be working with RMIT on this innovative project.

“We're taking those experiments and putting them in ground and in the field today, we're going to have people walking across the concrete that includes these products and RMIT is going to be coming back and doing testing to see how they stand up,” he said.

“Despite the fact that we're using coffee grounds or mulch, residents aren't going to really see or smell any difference in this concrete product.

It's really important for Council to be involved in projects such as this and to be working closely hand in hand with universities such as 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.

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

Aerial view of the finished footpath in Gisborne. The three panels attached to the footpath indicate different types of concrete used in the footpath, as part of the trial. The right panel indicates the section using coffee biochar in the concrete; the middle section uses wood chip biochar; the left section is the control, which uses standard concrete ingredients only. Credit: Chris Matthews, Macedon Ranges Shire Council

Turning coffee concrete into a commercial reality

The researchers will evaluate the performance of the concrete in these trial footpaths in Gisborne, with the aim of supporting the further roll out of this 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.

There are potential cost savings for construction companies and concreters if this RMIT innovation can be integrated into the supply chain.

“Our research creates a potential to even reduce the required cement content. 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.

Several other planned infrastructure projects around Victoria will also turn spent coffee grounds into biochar and transform this waste into a valuable 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 other circular-economy projects.

Support for the research

The authors acknowledge the support from ARUP Australia Pty Ltd, Earth Systems Pty Ltd and RMIT University, including the Strategic Capability Deployment Fund, Rheology and Materials Characterisation Laboratory, the X-Ray Facility and the Microscopy and Microanalysis Facility.

Publications

The team has published several peer-reviewed publications that provide evidence and analysis of their results related to these trials with Macedon Ranges Shire Council.

‘Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength’ is published in the Journal of Cleaner Production. (DOI: 10.1016/j.jclepro.2023.138205).

‘Carbon sequestration from waste and carbon dioxide mineralisation in concrete – A stronger, sustainable and eco-friendly solution to support circular economy’ is published in Construction and Building Materials (DOI: 10.1016/j.conbuildmat.2023.131221).

Key contact

Dr Rajeev Roychand
School of Engineering
STEM College

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