A group of scientists here is now trying to give coffee grounds a second act, putting the energizing substance into concrete — making it both stronger and more sustainable in the process.
In a cavernous workshop at a Royal Melbourne Institute of Technology campus on a recent day, Shannon Kilmartin-Lynch was preparing a batch.
He added charred used coffee grounds from a local roaster into a batch of gray sludge that will harden into the ubiquitous material of the modern urban downtown.
The substitution makes concrete 30 percent stronger than a control batch, according to an RMIT study published in last month’s Journal of Cleaner Production.
The innovation is an example of the creative approaches scientists have adopted in past years as they try to reuse materials and create a more sustainable world.
Building materials are now being viewed as potential depositories for recyclables and carbon that would otherwise escape into the atmosphere.
RMIT is working with 10 Australian local authorities to pave roads using thrown-out plastic. It has produced concrete partly made with used rubber tires; while the University of Sydney has embedded ground glass into theirs.
Kilmartin-Lynch, part of the five-member RMIT team working on the coffee project, approaches the task through an Indigenous lens. An Aboriginal scientist with a PhD in concrete sustainability, he said his cultural background led him to use his interest in civil engineering to care for the Australian environment.
“I wanted to be in that space to make a change,” he said.
Across two RMIT campuses in Melbourne, the coffee grounds are cooked at 662 degrees with little oxygen, a process called pyrolysis. The resulting substance, called biochar, is combined with concrete’s traditional ingredients: cement, water, gravel and sand, with biochar replacing 15 percent of the sand.
The university plans to conduct real-world field trials over the coming six months or so.
Coffee was chosen as a candidate simply because the researchers noticed how many cups of joe they were personally consuming, Kilmartin-Lynch said. But the process can be replicated with any organic material.
“This is really just an example,” he said. “It’s typically done with trees. We’ve done it with coffee alone. You know, it’s coffee, people love coffee.”
If this type of concrete was to become widely used, one benefit would be to the climate.
Organic waste releases greenhouse gas as it breaks down, whether in compost or landfill.
Millions of tons of it are produced each year: from the plant matter thrown away during farming, to the food waste of the typical household. Firing it into biochar and storing it in concrete keeps the carbon locked in solid form, where it can’t heat the planet.
Spent coffee grounds make up a significant proportion of the total organic waste going to landfill in Australia.
“This leads to the production of methane gas, which contributes significantly to climate change,” the RMIT scientists wrote in their paper. “Therefore, there is an urgent need to discover various recycling solutions that can help in diverting this waste from going to landfills into commercial applications.”
And it could contribute to a more “circular economy,” a model in which what would be waste is incorporated into other parts of life.
But Kypros Pilakoutas, managing director of the University of Sheffield Center for Cement and Concrete, who was not involved in the RMIT research, highlighted the logistical challenge of taking such a project beyond the proof-of-concept phase.
“The economic feasibility of such an application is highly doubtful,” he said in an email. “Even though I find this study intriguing from a technological perspective, I deem it highly improbable that it will ever find widespread use in large-scale applications.”
Kilmartin-Lynch has more of a blue-sky view.
“Hopefully, one day, all of your organic waste you can just empty into one big thing, put it through a fire pyrolysis, and send it out,” he said. He added that the team had not done industry costings at this stage.
Ali Abbas, director of the University of Sydney Waste Transformation Research Hub, who also was not involved in the RMIT project, said he saw it as part of a wave of promising research into concrete and sustainability globally that was proving effective within labs and field trials but was yet to break into the mainstream.
“We might be not many years away,” Abbas said. “However, the issue is beyond the technical.”
What was required to progress was to “take your engineering hat off and put your business hat on,” he said. Cost, the logistics of scaling and persuading construction safety regulators to accredit unorthodox materials are among the most pressing challenges.
Some research efforts focus on using concrete to store waste or even captured carbon dioxide.
Others are working on the vexing problem of reducing the carbon footprint of concrete itself, which primarily comes from cement.
Cement, a binding substance usually made primarily of limestone which produces carbon dioxide as a byproduct, comprises between 10 and 15 percent of the average slab of concrete. But it is responsible for the majority of its greenhouse gas emissions, and about 8 percent of all global emissions — more than aviation, and of most countries.
Alternative materials — including waste products from steel production and coal-fired electricity generation called “blast furnace slag” and “fly ash” — have so far struggled to make a significant dent in the product’s rising overall emissions.
“There is a lot of research in this area,” Abbas said.
While the recipe for today’s concrete was standardized in Britain in the 1820s, there is a long history of using organic matter in its manufacture.
China’s Great Wall is held together with a mortar partly made of sticky rice, and its pre-19th century builders made concrete of the same household substance. Pumice and volcanic ash were employed by Mesoamericans when constructing the still-standing city of El Tajin in Mexico about 1,000 years ago. In the ancient Mediterranean, experts say additives as varied as blood, milk and egg were used.
About two millennia later, Kilmartin-Lynch paid for a coffee and headed to the RMIT workshop, to work on adding what he was drinking to the list.