From beans to buildings: recycle coffee grounds to make eco concrete

New research by RMIT engineers published in the Journal of Cleaner Production shows how we could improve concrete by adding an everyday type of waste to it: spent coffee grounds  

How to manufacture stronger concrete through the usage of spent coffee grounds – Bio-waste

A team of engineers from the Royal Melbourne Institute of Technology (RMIT) have figured out how to manufacture stronger concrete through the usage of spent coffee grounds (SCG), creating a recycling solution that diverts organic waste from going into landfills and turns it into a resource. 

«The disposal of organic waste poses an environmental challenge as it emits large amounts of greenhouse gasses including methane and carbon dioxide, which contribute to climate change». said Dr Rajeev Roychand from RMIT University’s School of Engineering in a press release. 

Organic waste – an environmental challenge: effects on the climate, acidification, and eutrophication

Organic waste and bio-waste are umbrella terms utilized to refer to organic waste from a variety of streams. These include the food and beverage industry and industrial and municipal solid waste. 

According to a 2020 report by the European Environment Agency (EEA), biowaste makes up thirty-four percent of the municipal waste in the EU, making it the latter component. Of all bio-waste, around sixty percent of bio-waste is food waste. 

Biodegradable waste as a whole is responsible for around three percent of the European Union’s (EU) total greenhouse gas emissions (GHG) (EEA, 2019a), and it’s a chief source of GHG emissions from landfill sites. 

In fact, once it’s landfilled, biodegradable waste breaks down. At that point, it releases methane, a potent greenhouse gas with a potential for 100-year global warming twenty-eight to thirty-four times greater than Carbon Dioxide (CO2).

Total food waste’s combined effects on the climate, acidification, and eutrophication account for fifteen to sixteen percent of the overall food value chain’s environmental impact.

An overview of the impact of two resource-intensive industries: the concrete and construction industries 

Concrete is the most commonly used building material and the most extensively manufactured product on the planet by mass.

With the widespread use of cement comes an environmental impact. According to the London-based think tank Chatham House, sometimes referred to as the Royal Institute of International Affairs, cement production amounts to over 4 billion tonnes per year, leading to eight percent of CO2 emissions worldwide. 

The cement sector would need to curb its annual emissions by at least sixteen percent by 2030 to align itself with the goals of the Paris Agreement. In 2018, the buildings and construction sector as a whole was responsible for thirty-nine percent of final energy use and process-related carbon dioxide (CO2) emissions and thirty-six percent of total energy use.

 Against Bio-waste: Experimenting new materials for architecture

This material’s production requires various raw materials, such as limestone and clay. Cement is combined with aggregate, a coarse mixture of minerals like sand, stone, and water when making concrete. As these parts combine, they harden into the material that is used to build anything from roads and schools to single-family homes and skyscrapers.  

«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 Professor Jie Li, a researcher from RMIT University and one of the study’s authors.

There are substantial environmental effects from the continued extraction of natural sand to suit the demands of the construction industry. «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». Li said. «With a circular-economy approach, we could keep organic waste out of landfill and also better preserve our natural resources like sand».

Organic waste’s potential for circularity: tapping into alternative raw materials 

The prevention and the sustainable management of avoidable and unavoidable bio-waste is critical to reducing the environmental impact of bio-waste. Bio-waste can be part of a more circular economy and be employed in producing soil fertilizers, mulching, and biogas. 

This research leads the way to employ this type of unavoidable bio-waste in a different way. Australia alone produces seventy-five million kilograms yearly alone, while the whole world creates ten billion kilograms of ground coffee waste each year. 

Biowaste management: using coffee grounds to make stronger concrete

The study titled Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength by the RMIT was published in August 2023 in the Journal of Cleaner Production. 

The study details how this team has employed spent coffee grounds (SCG), an inedible and unavoidable type of food waste, to enhance concrete’s mechanical and physicochemical qualities.

If applied in the construction industry, the findings of this research could allow the industry to take part in building a more sustainable life cycle for coffee.  

«Inspiration for my research, from an Indigenous perspective, involves Caring for Country, ensuring there’s a sustainable life cycle for all materials and avoiding things going into landfill to minimise the impact on the environment». said Dr Shannon Kilmartin-Lynch, Indigenous Post-Doctoral Research Fellow at RMIT University’s the School of Engineering.

«The concrete industry has the potential to contribute to increasing the recycling of organic waste such as used coffee,» said Kilmartin-Lynch. «Our research is in the early stages, but these exciting findings offer an innovative way to greatly reduce the amount of organic waste that goes to landfill».

Circular Economy in manufacture – how can spent coffee grounds (SCG) be integrated into concrete? 

Spent coffee grounds might not sound like a material that could be employed in concrete production. In fact, because of its high organic content, SCG cannot be used in concrete as it is, and it’s an unsuitable replacement for construction materials. 

To make roasted, used coffee grounds into a suitable material for the research’s purposes, the researchers behind the “Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength” study employed pyrolysis. This process consists of heating organic materials at high temperatures in the absence of oxygen. This process thermally decomposes the organic material, yielding carbon-rich and porous biochar.

To prepare coffee biochar (CBC), the SCG was collected from several cafeterias and put in aluminum trays wrapped in pocked aluminum foil. The SCG were then pyrolyzed for two hours each at 350 and 500 °C. 

The analysis conducted on this concrete containing the CBC showed that the concrete’s hydration reaction and compressive strength are hampered by the organic chemicals that leach from spent coffee grounds (SCG).  

SCG that has been pyrolyzed at 350 and 500 °C formed a solid bond with the cement matrix. Using a fifteen percent volume replacement with spent coffee grounds that were pyrolyzed at 350 °C led to thirty percent stronger concrete. The study also showed that all of the waste SCG biochar (350CBC) can be employed in Australia as a fine aggregate (FA) replacement.

«Our research team has gained extensive experience in developing highly optimized biochars from different organic wastes, including wood biochar, food-waste biochar, agricultural waste biochar, and municipal solid-waste biochar, for concrete applications». said Dr Mohammad Saberian a civil engineer from the Royal Melbourne Institute of Technology.

Coffee ground integrated into concrete – The future of the research 

The researchers who worked on this study intend to work on practical implementation strategies and field trials and wish to work with industries to expand their research.

«The inspiration for our work was to find an innovative way of using the large amounts of coffee waste in construction projects rather than going to landfills – to give coffee a ‘double shot’ at life». said Dr Roychand, the study’s lead author.

«Several councils that are battling with the disposal of organic waste have shown interest in our work. They have already engaged us for their upcoming infrastructure projects incorporating pyrolyzed forms of different organic wastes».

RMIT

The Royal Melbourne Institute of Technology (RMIT) is an Australian public research university of technology, design and enterprise founded in 1887 in the capital of the Australian state of Victoria. 

Roberta Fabbrocino