Recycled coffee grounds make cement stronger, say scientists

Evidently, there is a sand shortage for making concrete, but researchers from RMIT University in Australia have determined that adding "pyrolyzed" or baked coffee grounds as a sand substitute makes the cement stronger!

Baking the grounds at precisely 350C, scientists produced a 29.3 percent increase in the compressive strength of concrete by substituting them for some of the sand. Perhaps Starbucks will soon have a branded line of cement to go with their routinely over-roasted beans! Seems like natural next step.


Coffee grounds can't simply be mixed in raw with standard concrete as they won't bind with the other materials due to their organic content, Dr. Roychand explained. In order to make the grounds more compatible, the team experimented with pyrolyzing the materials at 350 and 500 degrees C, then substituting them in for sand in 5, 10, 15 and 20 percentages (by volume) for standard concrete mixtures.

The team found that at 350 degrees is perfect temperature, producing a "29.3 percent enhancement in the compressive strength of the composite concrete blended with coffee biochar," per the team's study, published in the September issue of Journal of Cleaner Production. "In addition to reducing emissions and making a stronger concrete, we're reducing the impact of continuous mining of natural resources like sand," Dr. Roychand said.

"The concrete industry has the potential to contribute significantly to increasing the recycling of organic waste such as used coffee," added study co-author Dr Shannon Kilmartin-Lynch, a Vice-Chancellor's Indigenous Postdoctoral Research Fellow at RMIT. "Our research is in the early stages, but these exciting findings offer an innovative way to greatly reduce the amount of organic waste that goes to landfill," where its decomposition would generate large amounts of methane, a greenhouse gas 21 times more potent than carbon dioxide.