Finding new uses for coffee grounds could prevent them from emitting methane in landfills. Image source: New Scientist website

Australian scientists have found a new outlet for discarded coffee grounds: making stronger concrete. The research team has developed a technology that uses a low-energy, oxygen-free process that works at 350°C to turn waste coffee grounds into biochar, partially replacing the sand used to make concrete, and the strength of the newly obtained concrete has increased by nearly 30%. In addition, this method reduces the greenhouse gases produced by coffee grounds in landfills. Related papers were published in the latest issue of "Clean Production" magazine.

An estimated 18 million tons of spent coffee grounds are produced globally each year, most of which is sent to landfills, where they decompose and release methane, a greenhouse gas 21 times more potent than carbon dioxide.

The team collected used coffee grounds from several local cafes and investigated the feasibility of using them in place of some of the sand that is usually incorporated into concrete as filler. The results showed that in its natural state, replacing the sand component with discarded coffee grounds weakened the strength of concrete.

But when the researchers heated the coffee grounds in a furnace at 350°C in the absence of oxygen for 2 hours, they produced a charcoal-like biochar. Studies have shown that if this biochar is used to replace 15% of the sand in concrete, the resulting concrete bricks are 29% stronger than traditional bricks.

The addition of biochar makes the concrete stronger, the researchers explain, possibly because it has a porous structure that locks in moisture, preventing the interior of the concrete from drying out and creating microcracks that weaken its structural strength.