Home » Want a stronger concrete? Just add ‘coffee’ and stir

Want a stronger concrete? Just add ‘coffee’ and stir

by Mark Cantrell
Researchers in Australia claim concrete can be made 30% stronger by using processed coffee waste

We’re used to the idea that coffee fortifies the constitution, but we’re usually talking people – not concrete.

Well, engineers in Australia claim to have found a way to ‘upcycle’ used coffee grounds to make concrete up to 30% stronger.

Technically, it’s not the actual coffee grounds in itself, but what’s left over once they are processed.

The spent grounds are turned into so-called biochar through a process known as pyrolysis; that is they are heated to 350C without oxygen present.

The innovation represents something of a double hit, the researchers say: improving the strength of a common construction material, while avoiding dumping a common organic waste product into landfill.

Dr Rajeev Roychand, a postdoctoral research fellow from RMIT University’s School of Engineering, Australia, was a lead author of the paper, detailing the study in the Journal of Cleaner Production.

“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,” he said.

“The inspiration for our work was to find an innovative way of using the large amounts of coffee waste in construction projects rather than going to landfills – to give coffee a ‘double shot’ at life.

“Several councils that are battling with the disposal of organic waste have shown interest in our work. They have already engaged us for their upcoming infrastructure projects incorporating pyrolysed forms of different organic wastes.”

Australia generates 75m kilograms of ground coffee waste every year – most of it goes to landfill. Globally, 10bn kilograms of spent coffee is generated annually.

Sustainable life cycle

Joint lead author, Dr Shannon Kilmartin-Lynch, a Vice-Chancellor’s Indigenous Postdoctoral Research Fellow at RMIT, said construction industries around the world could play a role in transforming this waste into a valuable resource.

“Inspiration for my research, from an Indigenous perspective, involves Caring for Country, ensuring there’s a sustainable life cycle for all materials and avoiding things going into landfill to minimise the impact on the environment,” added Kilmartin-Lynch. from the School of Engineering.

“The concrete industry has the potential to contribute significantly to increasing the recycling of organic waste such as used coffee.

“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.”

Actually, there’s a third ‘hit’ for the process. There’s not just the matter of finding a new use for an otherwise waste product; there’s the added benefit of reducing consumption of another common – and finite – raw material – natural sand. Some 50bn tonnes of the material are used on construction projects globally every year.

Professor Jie Li, research team leader and corresponding author of the study, said the coffee biochar can replace a portion of the sand that was used to make concrete.

“The ongoing extraction of natural sand around the world – typically taken from river beds and banks – to meet the rapidly growing demands of the construction industry has a big impact on the environment,” Li said.

“There are critical and long-lasting challenges in maintaining a sustainable supply of sand due to the finite nature of resources and the environmental impacts of sand mining.

“With a circular-economy approach, we could keep organic waste out of landfill and also better preserve our natural resources like sand.”

Co-researcher Dr Mohammad Saberian said the construction industry needed to explore alternative raw materials to ensure its sustainability.

“Our research team has gained extensive experience in developing highly optimised biochars from different organic wastes, including wood biochar, food-waste biochar, agricultural waste biochar, and municipal solid-waste biochar, for concrete applications,” Saberian said.

Following their initial research, the team are planning to develop practical implementation strategies and work towards field trials. The team is keen to collaborate with various industries to develop their research.

Read next: Heathrow trials lower carbon concrete

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