Environment

Coffee grounds recycled as sustainable road material

Coffee grounds recycled as sus...
Professor Arul Arulrajah and his research team have figured out a new use for discarded coffee grounds
Professor Arul Arulrajah and his research team have figured out a new use for discarded coffee grounds
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Arulrajah and his research team gathered up coffee grounds from cafes around the university and dried them out in an oven for five days at 50° C (122° F)
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Arulrajah and his research team gathered up coffee grounds from cafes around the university and dried them out in an oven for five days at 50° C (122° F)
Professor Arul Arulrajah and his research team have figured out a new use for discarded coffee grounds
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Professor Arul Arulrajah and his research team have figured out a new use for discarded coffee grounds

Melbourne folk do love their coffee, and one day the beverage mightn't be just pepping them up for a day's work but paving the way for their trip into the office. Swinburne University researchers have scoured the campus' cafes for coffee grounds and used them as part of the mix for a more sustainable road construction material.

The research was led by Professor Arul Arulrajah who heads up the university's Centre for Sustainable Infrastructure. His work has focused on how other recycled materials like broken up brick, glass and concrete might be repurposed for use in more efficient road construction.

"I see the baristas throwing away the used coffee grounds and I think, 'why not look at this as an engineering material?'" he says.

So Arulrajah and his research team gathered up coffee grounds from cafes around the university and dried them out in an oven for five days at 50° C (122° F). They filtered the coffee to remove lumps and then mixed it with a waste product from steel manufacturing called slag, seven parts to three.

After adding a liquid alkaline solution to bind it all together, the team then compressed the mix into cylindrical blocks. Their testing showed that the blocks were robust enough to be used as a subgrade, the material that sits beneath the road surface.

Mounting environmental concerns over the impact of the coffee trade have spawned a number of imaginative uses for the many millions of tons of used grounds that are generated each year. These have included efforts to turn them into biofuels for single cars and even large cities, recycling them as a carbon capture material, and as the basis of universal robotic grippers.

The Swinburne University researchers say that if their approach was scaled up and they were given free rein over the city's discarded grounds, they could one day offer a greener path forward.

"On average the cafes we collect from dispose of about 150 kg (330 lb) of coffee grounds per week," says Professor Arulrajah. "We estimate that the coffee grounds from Melbourne's cafes could be used to build five kilometres (3.1 mi) of road per year. This would reduce landfill and the demand for virgin quarry materials."

The work was published in the journal Construction and Building Materials.

Source: Swinburne University

8 comments
notarichman
huh! use coffee grounds on your lawn in shady spots where the lawn doesn't grow well. no need to go through all the hoopla to recycle it.
WellFedEd
I'd rather drive on it then drink it. I drink tea which is a civilized drink.
CarolynR
This is a low grade use of a biological material which has higher value as a biofuel feedstock, as a source of pharmaceutical oils, as a raw material for charcoal-type blocks or as a source of nutrients for soil conditioning. It doesn't make sense to use energy to produce a road substrate. Have a look at UK company BioBean http://www.bio-bean.com/ who are already thriving commercially.
DonKirkwood
As an ecologist, I suspect it wouldn't take long for fungi, bacteria and plant activity to break down the coffee content of the mixture, resulting in subsidence and road failure. There's a reason engineers never permit soils with high organic content to be used in foundations, concretes, or roads. Used coffee grounds are a pretty attractive growing medium for anything from fungi to plants, with around 2% nitrogen and decent phosphorus levels. Better to use it to grow mushrooms, make compost or enrich soil directly. I cart home around 25-50kg of used coffee from my local roaster every week for my garden, and I have to compete to get it before anyone else does. Disposing of coffee should be a non-issue.
npublici
Quite a wasteful project,considering that coffee grounds are good fertilizer and biodegradeable.They are quite high in nitrogen.
Sergiuss
The coffee grounds can also be used in creams abrasive detergent to clean the dirty hands of grease in a workshop. The replacement of sand by coffee ground, as abrasive element of the hands cleaner, prevents clogging of sewage tubes.
Grainpaw
I have thought for a long time that chewing gum could be used to patch potholes.
Ralf Biernacki
Five days of electric oven drying. . . complex cleaning and forming process. . . adding slag (which is the actual load-bearing material here, the grounds are just a spacer). . . "alkaline liquid" additive. . . Just how do the financial and energetic (carbon footprint) costs of that compare to the costs of "virgin quarry material", i.e. gravel? <p> I haven't even mentioned the carbon footprint and logistic cost of collecting the grounds individually from cafes all over the city. <p> Not to overlook the fact that coffee grounds, unlike gravel, are biodegradable. especially in the presence of moisture which is unavoidable in the subgrade. How soon will the road subside? What will be the repaving cost, of which the cost of subgrade material is only a minuscule fraction?