Used coffee could be a smart solution for stronger concrete
By Tamanna Wadhwani 25 September 2023
RMIT University researchers have developed a unique method of reusing spent coffee grounds by converting them into biochar, which when mixed into concrete makes it 30 per cent stronger.
Australia is a highly caffeinated country. For many of us, coffee is an essential part of our morning routine and it is estimated Australians consume over 6 billion cups of coffee each year*.
That coffee compulsion creates substantial amounts waste, with thousands of kilograms of used coffee grind being sent to landfill. Researchers have been looking at potential solutions for the waste stream for years, and now a new potential solution has emerged from the construction sector.
A team of researchers at RMIT University’s School of Engineering recently devised a technique for making concrete 30 per cent stronger by adding biochar made from used coffee grounds.
Lead Postdoctoral Research Fellow Dr Rajeev Roychand and his team use a low-energy process involving heating coffee grounds to 350 degrees Celsius in an absence of oxygen. The process converts the grounds into ‘biochar’, giving coffee the potential for a second life in various applications and preventing it from going to landfill.
“The disposal of organic waste poses an environmental challenge as it emits large amounts of greenhouse gases including methane and carbon dioxide, which contribute to climate change,” said Roychand.
It is estimated that Australia produces around 75,000 tonnes of coffee waste every year, which according to RMIT’s researchers, has the potential to generate about 22,500 tonnes of coffee biochar.
According to Dr Roychand, if 15 per cent of the volume of sand used in making conventional concrete is replaced by coffee biochar, the resulting concrete can be up to 30 per cent stronger. Using biochar can also help cut down the cement content in concrete while still maintaining its strength as compared to conventional concrete.
“Based on our experience we anticipate that about 10 per cent reduction in the cement content can be achieved without compromising the strength properties of concrete,” said Roychand to Planet Ark.
The coffee biochar is also much lighter than the sand conventionally used to make concrete, with a density that is almost nine times lower. This could provide an important opportunity for the construction industry, which currently uses around 50 billion tonnes of natural sand in projects annually, to reduce its resource extraction. If the industry were to have a 100 per cent uptake of the coffee biochar replacement, the RMIT team estimate that around 198,750 tonnes of sand could be saved.
“The ongoing extraction of natural sand around the world to meet the rapidly growing demands of the construction industry – typically taken from river beds and banks – has a big impact on the environment,” said corresponding author and research team leader Professor Jie Li.
“With a circular-economy approach, we could keep organic waste out of landfill and also better preserve our natural resources like sand.”
The team of RMIT researchers will also be looking at other forms of organic waste currently being sent to landfill in Australia as potential construction materials. They anticipate that more than 70 per cent of Australia’s organic waste can be transformed into a high value product for concrete applications.
‘Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength’ is published in the Journal of Cleaner Production and can be viewed for more information.
*Based on 2014 research on SCGs in the Sydney City council area by Planet Ark with support from The City of Sydney.
Tamanna moved from India to Australia to pursue a degree in environmental science and conservation biology. After learning about the concept of a circular economy in 2020, she worked with various organisations in this sector and is interested in solving complex climate change and waste management problems. She loves to communicate with people about all things sustainability or animals. Outside of work, Tamanna is a budding hip hop dancer who also loves travelling, cat cuddles and reading.
