Turning Coffee Grounds into Concrete to Cut Waste and Save Sand

Researchers at the Royal Melbourne Institute of Technology (RMIT) in Australia have invented a way to tackle several problems at once.

Every year, an astonishing 10 billion kilograms of coffee waste are produced worldwide, and most of it ends up in landfills.

“The disposal of organic waste is an environmental issue, as it leads to the emission of a large amount of greenhouse gases, specifically methane and carbon dioxide, which contribute to climate change,” noted RMIT research engineer Rajiv Roychand.

The rapid growth of construction worldwide is driving up demand for resource-intensive concrete, which creates its own environmental problems. “The extraction of natural sand around the world (usually from riverbeds and shorelines) to meet the growing needs of the construction industry significantly impacts the environment,” emphasized Jie Li, a research engineer at RMIT.

He told ScienceAlert that “there are currently critical and long-term issues regarding sand supply due to resource limitations and the impact of sand extraction on the environment.” The university team says it is essential to keep organic waste out of landfills and to conserve natural resources such as sand.

What did the scientists learn?

Organic materials, such as coffee grounds, can’t be added directly to concrete because they release chemicals that weaken the building material. So, using relatively low energy, the team heated the coffee waste to temperatures above 350 °C in an oxygen-free environment.

This process, called pyrolysis, breaks down organic molecules and produces a porous, carbon-rich charcoal known as biochar. That biochar can bond with and integrate into a cement matrix.

Roychand and his colleagues also tried pyrolyzing coffee grounds at 500 °C, but the resulting biochar particles were weaker.

The team still needs to assess the long-term strength of the cement. They are testing the hybrid coffee cement’s behavior in freeze/thaw cycles, water absorption, and other stress conditions.

The researchers are also working on producing biochar from other organic waste, such as wood, food, and agricultural waste.

“Our research is currently in the early stages, but these discoveries offer an innovative way to significantly reduce the amount of organic waste sent to landfill,” noted Shannon Kilmartin-Lynch, co-author of the study.

The results of the study were published in the Journal of Cleaner Production.