Coffee grounds in concrete: How your morning coffee can revolutionize the construction industry

Did you know that your daily morning coffee can help make the construction industry more sustainable? Sounds crazy, but that's exactly what's happening! In Australia, around 75,000 tonnes of coffee grounds are generated each year, which normally end up in landfills and release methane, an extremely harmful greenhouse gas. But Roychand et al. published a paper in the Journal of Cleaner Production in 2023 and showed that coffee grounds - if treated properly - can be a valuable resource for concrete production. By converting coffee grounds into biochar through pyrolysis, it could replace natural sand in concrete mixes in the future, solving several environmental problems at once. Read on to learn how your coffee can change the world!

Sandcastles made from coffee grounds? The plight of sand mining

Disposing of organic waste is a major environmental burden, as its decomposition produces greenhouse gases such as methane, which is 21 times more harmful to the climate than CO2. Carbon dioxide, nitrous oxide and ammonia are also released. A significant part of this waste is spent coffee ground (SCG). In Australia alone, around 75,000 tonnes of coffee grounds are generated each year, much of which ends up in landfills where they release methane, which contributes significantly to climate change. Therefore, it is urgent to find recycling solutions to convert this waste into commercially usable resources while reducing greenhouse gas emissions.

Parallel to the problem of organic waste is the construction industry's ever-increasing demand for natural sand, the mining of which causes serious environmental and sustainability problems. The construction industry must therefore find alternative raw materials to ensure its long-term sustainability. Previous research shows that the concrete industry has great potential to utilize various industrial by-products and wastes, such as fly ash, slag, glass, tires and plastic.

From waste to building material: coffee grounds in the construction industry

Due to their fine particle size, coffee grounds have been investigated for various applications in construction. However, studies have shown that untreated coffee grounds significantly reduce the compressive and flexural strength of concrete. For example, the addition of 20% coffee grounds as a replacement for fine sand resulted in a 44% decrease in compressive strength and a 68% decrease in flexural strength after 28 days. Similar negative effects have been observed when coffee grounds are used in ceramic materials.

Hot beans: Pyrolyzed coffee grounds as a savior

In its natural form, coffee grounds are not a suitable replacement for building materials. However, studies have shown that positive results can be achieved by pyrolyzing coffee grounds. Pyrolysis involves decomposing organic waste at high temperatures in the absence of oxygen, producing carbon-rich, porous biochars. Studies have shown that adding coffee ground-based activated carbon to mortar samples increases compressive strength.

Effects of different pyrolysis temperatures

A comprehensive research project investigated the application of raw and pyrolyzed coffee grounds treated at 350°C and 500°C as a replacement for fine sand in concrete. The results showed that the addition of 5% coffee grounds significantly affects the compressive strength because organic compounds interfere with the hydration reaction of the cement particles. In contrast, pyrolyzed coffee grounds at 350°C (350CBC) significantly improved the compressive strength of the concrete, especially at a replacement rate of 15%.

From espresso to building material: The practical application

Australia produces around 75,000 tonnes of coffee grounds annually, which can be processed into around 22,500 tonnes of biochar through pyrolysis at 350°C. This biochar can be used in the construction industry as a replacement for fine sand, allowing for a significant increase in concrete strength and sustainable use of the waste.

Environmental benefits

This project provides an environmentally friendly way to dispose of organic waste and reduces methane emissions, which are 21 times more damaging to the climate than CO2, while reducing dependence on the continuous mining of natural resources for concrete.

Economic and social benefits

The use of biochar in construction creates a new industry that offers direct and indirect employment opportunities along the entire value chain. This has both economic and social benefits and contributes to the creation of a closed economic cycle.

Conclusion: The revolution in your cup

This study has shown that pyrolysis of coffee grounds at 350°C leads to a significant improvement in concrete strength. The use of 350CBC offers a sustainable solution for the construction industry and contributes to the reduction of greenhouse gas emissions. Further long-term mechanical and durability tests are necessary to further explore the application of 350CBC in the construction industry.

The future of the construction industry could be made significantly more sustainable and environmentally friendly through the innovative use of organic waste such as coffee grounds.