Engineers at RMIT University in Melbourne, Australia, have developed a method to turn leftover coffee grounds into biochar that can replace scarce construction sand, boost concrete strength and cut the volume of waste sent to landfills, infohub.kz reports.
The findings were published in the Journal of Cleaner Production. The technology makes construction concrete almost a third stronger by adding charred coffee grounds. The method is designed to tackle two global environmental problems at once: disposing of billions of kilograms of organic waste and curbing the depletion of natural river sand, which is mined on a massive scale for the construction industry.
The world produces about 10 billion kilograms of spent coffee grounds each year, most of which is dumped in landfills, releasing methane and carbon dioxide. Raw grounds cannot be added to cement because the organic matter releases substances that break down the mix. To get around this, the engineering team led by Rajeev Roychand used low-energy pyrolysis, heating the waste to more than 350 degrees Celsius without oxygen. The result was a porous carbon biochar able to bond firmly with the mortar matrix.
Experiments showed that particles heated to 500 degrees lost strength, while the 350-degree process produced concrete up to 30% stronger. The authors are now assessing the material's durability under temperature swings, abrasion and moisture, and are testing similar processing of wood and agricultural waste.
The technology has already moved to practical trials in road construction. In the Australian state of Victoria, the coffee-biochar mix was used to pour footpaths in the city of Gisborne and at a major infrastructure site in Pakenham. According to project contractor BildGroup, that single pour alone diverted the grounds of about 140,000 cups of coffee from landfill and saved more than three tonnes of valuable natural sand. The developers are preparing to bring the material to the commercial construction market.