Coffee Grounds Used to Strengthen Concrete

Scientists in Australia have discovered that coffee grounds can be used to make concrete up to 30% stronger.

The discovery by engineers at The Royal Melbourne Institute of Technology (RMIT) could help to solve three problems at once - the strength of concrete, greenhouse gas emissions and the depletion of natural resources.

All of which could be very good news indeed. 

Coffee Grounds and Greenhouse Gas Emissions

Most coffee waste currently ends up in landfill and that is a major issue as around 10 billion kilograms of waste is produced across the world each year. When placed in landfill, that waste emits greenhouse gasses which contribute to climate change.

Food waste is certainly a serious problem.  According to the UN Framework Convention on Climate Change and the Waste and Resources Action Program, wasted food generates approximately 8% to 10% of global greenhouse gases. That's five times more than the global aviation industry!

The treatment of coffee waste could represent a significant step forward in tackling greenhouse gasses.

Depletion of Natural Resources

A booming global construction market is also problematic for the environment as it increases the demand for concrete which is a resource-intensive product.

Concrete necessitates the extraction of sand and gravels which are finite resources.

Replacing a portion of natural river and quarry sand used in concrete will help to reduce pressure on global sand and gravel deposits. The new recipe evolved by the team at RMIT replaces 15% of the sand in concrete with treated coffee ground.

The Pyrolysis Process

Coffee grounds cannot be added directly to concrete mixes as they will leach chemicals that actually weaken the strength of the finished material.

In a process called pyrolysis, the team heated coffee waste to over 350 °C while depriving it of oxygen. During this process, the organic molecules are broken down creating a porous material called biochar. This can bond effectively with the cement matrix.

Real World Testing

Of course, the new and innovative form of concrete had to be tested in the real world to ensure it would perform well under the pressures of freezing, thawing, water absorption and any other stressors.

In 2024, RMIT worked with Macedon Ranges Shire Council to test the new concrete. A footpath was poured in Gisborne, Victoria. This was poured in three sections, one featuring the coffee-biochar concrete, one with wood chip biochar concrete and one with conventional concrete.

Later in 2024, coffee-biochar concrete was used to create a footpath during the Pakenham Roads Upgrade, a major infrastructure project.

During this real-world testing, the coffee-biochar concrete matched rather than exceeded the strength of standard concrete. While initial laboratory testing by the researchers showed that replacing 15% of the river sand with coffee biochar could increase concrete strength by up to 30%, the commercial kilns used to scale up production for the Pakenham project delivered a mix that matched, rather than exceeded, standard concrete. 

However, the project was still considered to be a success.

The Canary Wharf Structural Pours (London, UK)

All projects involving coffee-biochar concrete are being closely monitored to establish the long-term impacts of using the material. Meanwhile scientists are exploring the potential of other organic materials to enhance concrete.

You can find out how you can make better use of coffee grounds here.