Researchers at RMIT University in Australia teamed up with Macedon Ranges Sire Council to construct the world’s first coffee concrete footpath.

Organic waste going to the landfill, including spent coffee grounds, contributes 3 per cent of greenhouse gas emissions. In Australia alone, 75 million kilograms of ground coffee waste is generated every year, most of which ends up on the landfill. Coffee grounds have many uses, and one of them is use in concrete.

Of course, it cannot be added directly into the concrete mix, because, as organic material, it would decompose over time, weakening the concrete. To overcome this problem, the RMIT team turned the coffee grounds into biochar, using a low-energy process without oxygen at 350 degrees Celsius. The same principle can be used for other organic waste.

Adding the biochar into the concrete mix increases its strength by 30 per cent. It reduces the required cement content by as much as 10 per cent. The biochar replaces up to 15 per cent of sand that is used to make concrete, a material that is becoming increasingly scarcer. Globally, 10 billion kilograms of spent coffee is generated annually, which could replace up to 90 billion kilograms of sand in concrete.

For the trial, concrete made with coffee- and wood-based biochar will be used to make footpaths, though the cement content has not been reduced. The researchers will evaluate the performance of the material. They will later experiment using less cement.

Photos: Carelle Mulawa-Richards / Chris Matthews / RMIT University