Researchers at RMIT in Australia found that concrete can be made up to 30% stringer by replacing part of the sand with spent coffee grounds.

Worldwide, 54 million tonnes of spent coffee grounds are generated annually, worldwide. Most of this waste ends up on the landfill.

Due to their fine particle size, coffee grounds can be a useful component in civil and construction applications. To use them in concrete, the researchers dried the spent coffee grounds to remove the moisture. Then, the grounds were turned into biochar by heating them at either 350 degrees Celsius or 500 degrees Celsius in a low-energy, oxygen free process called pyrolysis.

Then, the different grounds were incorporated in Portland cement at 0%, 5%, 10%, 15% and 20% volume as a replacement for fine aggregate, in this case sand. After the concrete was cast and dried, they were tested for strength.

The researchers found that the one that replaced 15% of sand with coffee grounds pyrolysed at 350 °C (662 °F) led to a significant improvement in its material properties, resulting in a 29.3% enhancement in compressive strength.

While in the early stages, the promising results imply that sand, a dwindling resource, could be replaced in part by coffee grounds.

Photo: Carelle Mulawa-Richards, RMIT University