Concrete Can Be Made Stronger By Adding Coffee Grounds To It

Concrete can become 29% stronger when recycled coffee grounds are added to it, a team of scientist Rajeev Roychand from RMIT University in Melbourne, Australia.

First, the scientists collected coffee grounds from coffee shops in Melbourne and dried them to remove moisture. Then the dried material was heated at two different temperatures – 350 and 500 degrees Celsius. To do this, scientists used the process of pyrolysis to produce biochar from the ground.

Further, the researchers worked with two groups of mixture compositions, in which biochar based on spent coffee grounds and sand were used as fine aggregates, respectively. To make a concrete mix, different proportions of biochar and sand were added to Portland cement: 5, 10, 15 and 20%.

The resulting mixtures with different proportions of filler were poured into molds and air cavities were removed by vibration.  The finished concrete was then removed from the molds and placed in a tank of water to fully cure. After that, concrete at different temperatures (350 and 500 degrees Celsius) was tested for compressive strength, that is, they checked how much pressure it could withstand.

Unmodified coffee grounds have been found to weaken concrete when replacing sand, however when heated in a kiln at 350°C for 2 hours, a substance similar to charcoal/biochar is formed: replacing 15% of the sand in the concrete with it produced concrete blocks,  which were 29% stronger than normal.