Unlocking the Strength of Concrete: Harnessing the Power of Spent Coffee Grounds
Coffee grounds have the potential to enhance the strength and sustainability of concrete, claim researchers from RMIT University This innovative use of a high-value by-product can create tiny reservoirs within the concrete, resulting in a greener and more resilient construction material
If you can't start your morning without coffee, don't worry, you're not alone. Every day, people around the world consume more than 2 billion cups of coffee, resulting in a staggering 60 million tons of wet, spent coffee grounds annually.
Unfortunately, only a small fraction of these grounds are repurposed, mostly as soil fertilizer. The majority, on the other hand, are either burned or thrown into landfills. Like other organic substances, coffee grounds decompose in landfills, releasing methane - a greenhouse gas that is 25 times more potent than carbon dioxide when it comes to trapping heat.
However, a recent study has revealed that coffee grounds could serve as a valuable ingredient in concrete, with the potential to even enhance its strength.
"We came up with this idea while enjoying a cup of coffee," says Rajeev Roychand, a research fellow at RMIT University in Melbourne, Australia, who led the study. "By roasting the used coffee grounds without oxygen, we obtained a substance called biochar. When we substituted it for sand in concrete, it resulted in a 30% increase in the material's strength."
Tiny reservoirs
Concrete, the most commonly used construction material worldwide, is composed of water, gravel, sand, and cement. The global consumption of concrete has significantly increased over the past four decades, reaching a staggering 30 billion tons per year, three times its volume 40 years ago.
In an attempt to enhance concrete's properties, Roychand and his team experimented with substituting sand with biochar, a charcoal-like material derived from coffee waste. After extensive trials, they achieved the most favorable outcome by replacing 15% of the sand and subjecting the mixture to a temperature of 350 degrees Celsius (662 degrees Fahrenheit). As a result, the resulting concrete exhibited a 30% increase in compressive strength, indicating its improved ability to withstand applied loads.
Dr. Rajeev Roychand, Dr. Mohammad Saberian, and Dr. Shannon Kilmartin-Lynch from RMIT University, along with Jordan Carter, co-founder of Talwali Coffee Roasters, pose from left to right in the image.
At RMIT University, Carelle Mulawa-Richards explains that in standard concrete, water, which makes up a significant portion of its volume, gradually gets absorbed by the cement. As a result, the moisture content within the concrete decreases, leading to desiccation. This desiccation process, in turn, causes shrinkage and microscale cracking, ultimately compromising the strength of the concrete.
Biochar derived from coffee waste has the ability to mitigate this natural process. When integrated into concrete, the particles of biochar function as small reservoirs of water, dispersed throughout the concrete. As the concrete solidifies and sets, the biochar gradually releases the water, effectively rehydrating the surrounding materials and diminishing the occurrence of shrinkage and cracks.
According to Roychand, "Not only would we be diverting this waste and converting it into a valuable resource, but we would also be addressing the scarcity of sand. By substituting a portion of sand with biochar or other waste materials, we would enhance the sustainability aspect. Eventually, we may reach a point where a significant proportion of sand can be substituted with various waste materials."
âHigh-value by-productâ
The study, which was not associated with Kypros Pilakoutas, a professor of construction innovation at the University of Sheffield in the UK, has captured attention due to its technological implications.
However, he doubts that this method of producing concrete will gain significant traction in large-scale applications due to the challenges associated with waste collection and processing. He acknowledges that while it would be ideal to gather coffee grounds nationwide, the expenses involved are substantial and restrictive.
Moreover, he highlights that the process of pyrolysis, which generates the biochar, is not without costs. Additionally, he is skeptical about the notion that high levels of carbon in concrete would improve its long-term durability.
Roychad emphasizes that waste collection is already widely practiced, with several Australian companies prioritizing the recycling of coffee waste. He notes that the cost of pyrolysis primarily involves the initial investment in equipment, and highlights that biochar is produced at a considerably lower temperature than cement, at 350 degrees Celsius compared to approximately 1,450 degrees Celsius. However, Roychad argues that there are other overlooked advantages, as waste materials that end up in landfills necessitate disposal costs, whereas they can now be converted into valuable by-products.
According to think tank Chatham House, cement, a key component of concrete, is the main contributor to climate change, accounting for 8% of global CO2 emissions in 2021. Roychand suggests that by enhancing the strength of concrete by 30%, it becomes feasible to reduce the cement content by up to 10%, thereby decreasing its climate impact.
According to him, the discovery has generated interest from construction companies and coffee grounds recycling organizations. Currently, his team is collaborating with local councils in Australia to conduct field demonstrations. "Our plan includes monitoring the concrete for a duration of six months to one year to ensure the longevity of biochar's properties," he explains.
