Every year the world produces a staggering 10 billion kilograms of coffee waste and most of it ends up in landfills.

“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,” explained RMIT University engineer Rajeev Roychand.

With a booming construction market globally, there’s also an increasing demand for resource intensive concrete causing another set of environmental challenges.

“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,” said RMIT engineer Jie Li.

“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.”

Organic products like coffee grounds can’t be added directly to concrete because they leak chemicals that weaken the building material’s strength. So using low energy levels the team heated coffee waste to over 350 °C (around 660 °F) while depriving it of oxygen.

This process is called pyrolysing. It breaks down the organic molecules, resulting in a porous, carbon-rich charcoal called biochar, that can form bonds with and thereby incorporate itself into the cement matrix.