You won’t believe what it can be used for

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If your breakfast can’t be without coffee, you’re not alone: ​​globally, we drink over 2 billion cups of coffee every day, resulting in 60 million tons of used coffee grounds every year.

Only a small part of this is reused – mainly as a soil conditioner – with the vast majority being incinerated or ending up in landfills. There, like other organic compounds, coffee grounds decompose and release methane, a greenhouse gas 25 times more powerful than carbon dioxide at trapping heat.

But now researchers say coffee grounds could be used as an ingredient in concrete, and could even make it more durable, according to a recent study.

“We came up with this idea over a cup of coffee,” says Rajeev Roychand, a researcher at RMIT University’s School of Engineering 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 provided a 30% increase in the strength of the material.”

Roychand and his team partially replaced the sand with biochar – a material similar to charcoal – derived from coffee grounds. They achieved the best result when they replaced 15% of the sand and baked the grounds at 350 degrees Celsius. The resulting concrete was 30% stronger than normal based on compressive strength – the material’s ability to withstand a load.

In regular concrete, water, its second-largest component by volume, is absorbed by the cement over time, reducing the amount of moisture still in the concrete, Roychand says. This drying effect, known as desiccation, causes micro-scale shrinkage and cracking, weakening the concrete.

Biochar from coffee waste can reduce this natural process. When biochar is mixed with concrete, Roychand says, its particles act like tiny reservoirs of water, which are distributed throughout the concrete. As the concrete sets and begins to harden, the biochar slowly releases the water, effectively hydrating the surrounding material and reducing the impact of shrinkage and cracking.

“High value by-product”

According to Cyprus Pilakouta, professor of manufacturing innovation at the University of Sheffield in the UK, who was not involved in the work, the study is interesting from a technological point of view.

However, he considers it unlikely that concrete produced in this way will ever find widespread use in large-scale applications. “While it would be great to collect all coffee grounds from across the country, the costs involved would be significant and prohibitive.”

He adds that pyrolysis – the process through which biochar is produced – is expensive and he believes it is unlikely that high concentrations of carbon in concrete will enhance its long-term durability.

Roychad on the other hand points out that many companies in Australia are already 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 degrees Celsius compared to around 1,450 degrees Celsius. “But we lose other benefits,” he argues, “since the waste that ends up in landfills requires costs for its disposal. Now it can be turned into a high-value by-product.”

The concrete component that contributes the most to climate change is cement – which was responsible for 8% of global CO2 emissions in 2021, according to think tank Chatham House – and Roychand believes that increasing the strength of concrete by 30 % makes it viable to reduce the cement content by up to 10%, reducing its impact on the climate.

Source: HuffPost Greece



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