Australian engineers say they can make concrete almost 30 per cent stronger by adding treated coffee grounds.
The world produces about 10 billion kilograms of coffee grounds a year, most of which end up in landfill. Disposing of this organic waste presents an environmental challenge, as it releases potent greenhouse gases such as methane and carbon dioxide, contributing to climate change.
Meanwhile, the construction industry's global boom has created another set of environmental challenges, with the extraction of natural sand from rivers and beaches to meet growing demand having a major environmental impact.
"By taking this approach, we can divert coffee grounds from landfill and at the same time conserve precious natural resources such as sand," said RMIT University engineer Dr Jie Li.
Organic products such as coffee grounds cannot be added directly to concrete because they release chemicals that reduce the strength of the building material. So the team heated the coffee grounds to 350C in the absence of oxygen.
This process, called pyrolysis, breaks down the organic molecules in the coffee grounds, creating a porous carbon-rich material called biochar, which bonds well with cement.
They then substituted some of the sand normally used in concrete with the biochar made from the coffee grounds. This involved heating the waste coffee to around 350C to create the biochar. The researchers found that replacing 15 per cent of the sand normally used in concrete with coffee-derived biochar increased the strength of the concrete by 29.3 per cent.
"The idea stemmed from our desire to find a way to reduce coffee waste," said Dr Shannon Kilmartin-Lynch, who co-led the research.
The team are now working with local councils on potential infrastructure projects such as footpaths and bike paths, arguing that the technique could deliver environmental benefits by reducing the amount of coffee grounds going to landfill, as well as the demand for natural sand in construction.
Food waste makes up about 3 per cent of Australia's annual greenhouse gas emissions, according to the National Food Waste Strategy Discussion Paper. Australia produces an estimated 75,000 tonnes of coffee grounds waste each year.
The researchers calculated that if all of Australia's discarded coffee grounds were converted into biochar, it would result in about 22,500 tonnes of the material.
Summary
Australian engineers have found a way to make concrete almost 30 percent stronger by adding treated coffee grounds. This could help to reduce the amount of coffee grounds going to landfill and the demand for natural sand in construction, both of which have environmental benefits.