By Andrea Hargraves 
Concrete consists of four basic components: water, gravel, sand, and cement. In this study, sand was partially replaced with biochar – a material similar to charcoal – derived from coffee waste. The resulting concrete was 30% stronger than regular concrete
If your morning can't start without coffee, you're not alone: all over the world, We drink more than 2 billion cups of coffee every dayWhich leads to 60 million tons of coffee Wet and dilapidated every year.
Only a small portion is reused – mainly as soil fertilizer – and the vast majority is burned or deposited in landfills. There, like other organic compounds, the coffee grounds decompose and release methane, a greenhouse gas. 25 times stronger of carbon dioxide to retain heat.
Now, researchers claim that ground coffee can be used as an ingredient in concrete. It can make you strongeraccording to a recent study.
“We came up with this idea over a cup of coffee,” says Rajeev Roychand, a researcher at the School of Engineering at RMIT University in Melbourne, Australia, who led the study. “We roasted the used coffee grounds in the absence of oxygen and got something called biochar. When we added it to concrete as a substitute for sand, it increased the strength of the material by 30%.”
Small tanks
Hey Cement It consists of four basic components: water, gravel, sand and cement. It is the most widely used and expendable building material in the world 30 billion tons annuallythree times more than 40 years.
Roychand and his team partially replaced the sand with biochar — a material similar to charcoal — derived from coffee waste; They got the best result when they replaced 15% of the sand and cooked the grains at 350°C. The resulting concrete was 30% stronger than regular concrete in terms of compressive strength – the ability of the material to bear a load.
From left to right, researchers from the Australian university RMIT, Rajeev Roychand, Mohammad Sabarian, and Shannon Kilmartin-Lynch, with Jordan Carter, co-founder of Talwali Coffee Roasters. Caryl Molawa-Richards, RMIT University
In regular concrete, cement absorbs water, the second largest component by volume, over time, reducing the amount of moisture that remains within the concrete, explains Roychand. This drying effect, known as dehydration, causes shrinkage and microscopic cracks, weakening the concrete.
Coffee waste biochar can reduce this natural process. When biochar is mixed with concrete, its particles act like little reservoirs of water, distributed throughout the concrete, Roychand says. As the concrete sets and begins to harden, the biochar slowly releases water, essentially re-wetting the surrounding materials and reducing the effect of shrinkage and cracking.
“We will transform this waste and turn it into a valuable resource,” says Roychand. “There is also a shortage of sand, and even if we replace a portion of it, we are improving the sustainability aspect and can slowly reach a stage where a significant portion of the sand can be replaced with different waste materials.”
“High value by-product”
According to Kyros Bellakotas, professor of building innovation at the University of Sheffield in the UK, who was not involved in the research, the study is interesting from a technological point of view.
However, he believes that concrete produced in this way is unlikely to find widespread use in large-scale applications. “The main problem with waste is mainly its collection and treatment,” he points out. “While it would be great to collect all the coffee grounds in a country, the costs associated with that would be significant and expensive.”
He also adds that pyrolysis – the process by which biochar is produced – is not free, and he believes high concentrations of carbon in concrete are unlikely to increase its long-term durability.
Roychad highlights that waste collection is already a common practice and many companies in Australia are focusing on recycling coffee waste. He adds that the cost of pyrolysis is mainly related to the initial investment in equipment and that biochar is produced at a much lower temperature than cement – 350°C compared to about 1,450°C. “But we are missing out on other benefits,” he says, “because the waste that ends up in landfills requires disposal costs. Now it can be turned into a high-value by-product.”
The most climate-change-contributing ingredient in concrete is cement, which was responsible for 8% of global carbon dioxide emissions in 2021, according to a UN report. Think tank Chatham House – Roychand believes that increasing concrete strength by 30% makes it possible to reduce cement content by up to 10%, reducing its climate impact.
According to Roychand, this discovery has already attracted interest from construction companies and organizations that recycle coffee grounds, and his team is now working with local authorities in Australia to begin field demonstrations.
“One of the things we will do is monitor the concrete over time, for six months to a year,” he adds. “This will ensure that the biochar retains its properties over time.”