A footpath in regional Victoria is paving the way for an alternative approach to concrete – using waste coffee grounds and other organic material instead of sand
RMIT University has teamed up with Macedon Ranges Shire Council in Victoria to conduct a world-first coffee concrete footpath trial.
Several other upcoming infrastructure projects around Victoria will also turn spent coffee grounds into biochar and showcase how this simple product can have huge benefits for Australia’s construction industry.
Led by a team from the School of Engineering at RMIT, the researchers are looking for viable ways to achieve a circular economy where organic waste is reused in building material rather than being dumped in landfill, where it would otherwise decompose and produce greenhouse gases.
However, not only is there scope to replace sand in the concrete process with organic waste biochar, but it has been shown that the biochar actually increases the strength of the finished concrete by 30 per cent.
Earthmovers & Excavators spoke with project lead Dr Rajeev Roychand to find out how the team went from a pile of coffee grounds to a groundbreaking approach to improving sustainability in the construction industry.
Inspiration strikes
When asked how the idea of using waste coffee grounds in concrete came about, Roychand says that the team was looking for a way to transform organic waste into a reusable product and discussing ideas over a cup of coffee.
“As we were drinking coffee, we thought ‘why not start with coffee waste?’,” he says.
“So, this is what we first looked at when approaching the larger issue of organic waste ending up in landfills and how to reduce the resulting greenhouse gas emissions.
“We started with the raw spent coffee grounds but found that it was significantly hampering the strength of the concrete. The issue was the organic compounds being released during the cement hydration process, which were hindering the binding reaction.
“The next step was to modify its structure so that no organic compounds were left, but we didn’t want to burn the coffee because this process would again create greenhouse gases. So, we developed a low energy process that basically roasts the organic waste at about 350 degrees centigrade in the absence of oxygen to create a biochar.”
The team found using this biochar as a replacement for sand in the concrete mix provided a benefit – significantly increasing the strength of the finished product through the prevention of microcracking.
“The carbon-rich porous structure of biochar acts as microscale reservoirs that replenish water when concrete needs it,” Roychand says.
“As you might have seen in a footpath or other concrete structure, it can develop microcracks, but replenishment of microscale moisture reduces shrinkage and microcracking and increases the concrete strength.
“Within our subsequent work, we will focus on how different organic materials and different quantities used in concrete affect this further.
“Sand is getting scarce over time, and this waste can replace up to 15 per cent of the sand in concrete. We can also look at reducing the amount of cement used.”
Gisborne footpath
As a proof of concept, a concrete footpath was poured at the beginning of May in the regional Victorian town of Gisborne, containing coffee waste biochar, with plans for additional footpaths using biochar made from wood chips sourced from green waste generated by council landscaping work.
“It’s very exciting to see this world-first trial of our coffee and wood-based biochar in these footpaths collaborating with Macedon Ranges Shire Council,” Roychand says.
“We have already passed the 28-day design point and it’s looking fantastic. The council is very happy, and we have subsequent field trials planned to take place with the construction company.
“The council was proactive in supporting us, which was great because there can be concerns that what works in the lab doesn’t work in the field and there are costs involved. Now that this field trial has been successful there’s been a lot of interest from other construction companies.”
Roychand says that discussions are already underway as to how to turn this idea into a commercial reality for concrete contractors, with input being sourced from waste collection businesses and a multinational coffee chain. There is also the potential to expand into other organic waste streams to expand the benefits further.
“We are currently working on all different forms of organic waste from food processing facilities and agriculture,” Roychand says.
“Our future work will even cover residential organic wastes like vegetable and fruit peels, etc.”
He adds that the potential benefits of this research could be significant for contractors, particularly with the government actively promoting a closed loop economy.
“There’s the potential to reduce the amount of cement used, there’s a significant increase in strength and contractors will be supporting the diversion of waste, which is currently ending up in landfills,” Roychand says.
“There’s no downside to it.”
The team has published several peer-reviewed publications that provide evidence and analysis of their results related to these trials with Macedon Ranges Shire Council. For more information, please contact Dr Rajeev Roychand at rajeev.roychand@rmit.edu.au.