Could Coffee Grounds Really Make Concrete Stronger? Scientists Are Testing It

Americans drink more than 517 million cups of coffee every single day, and while there are plenty of genius ways to use coffee grounds in the yard and garden, an awful lot just goes in the trash. In fact, as much as sixty million tons every year goes into landfills. So the idea of using coffee grounds to make concrete stronger could be both money-saving and environmentally friendly. The big question is whether it actually works.

It seems that it does. After a sequence of experiments, scientists at the Royal Melbourne Institute of Technology (RMIT) in Australia have had considerable success. Their study, published at Science Direct, indicated that they added between five and 20 percent of spent coffee grounds to a concrete mix and found the sweet spot was 15 percent. At that ratio, they could increase the strength of concrete under pressure by an impressive 30 percent.

The secret is a technique called pyrolyzing, which heats the grounds while removing oxygen. The resulting material is called biochar. It is high in carbon and also porous, so it's easy to mix in with cement, aggregates, sand, and water when making concrete.

The biochar not only improved strength but also reduced cracking and increased durability. In terms of environmental benefits, it could cut down on landfill and greenhouse gases and also reduce the amount of sand that needs to be mined for concrete production.

Unfortunately, if you're thinking of saving up your coffee grounds for when you decide to build that DIY concrete patio to add style to your yard, you might have to wait a while. Plus, you'll probably have to settle for something weaker than the version the scientists created. They discovered that the optimum temperature to heat the coffee grounds to get the best performance from the biochar was 350 degrees Celsius (662 degrees Fahrenheit). Most household ovens won't exceed 550 degrees Fahrenheit.

However, there are still some interesting possibilities. Another group of scientists from Malaysia has been working on the idea of adding coffee grounds without first turning them into biochar. Results shared in the study, published by Discover Applied Science, have been encouraging, with a 12.6 percent strength gain. Experiments and tests are ongoing, so while there are a number of things you shouldn't do with coffee grounds around the home, adding them to your DIY concrete mix for increased strength might soon be a practical reality.