Concrete jungle: Turning coffee into concrete

Civil engineering students from RMIT University are replacing sand in cement mixture with coffee grounds to reduce landfill and ease the strain on the world’s sand supplies.

Just as the world’s viable coffee producing regions are under threat due to climate change, the world’s sand supplies are also diminishing.

According to Sand and Sustainability, a study by the United Nations Environment Programme, after water, sand is the most extracted mineral in the world. It is used to produce concrete, glass, and many other essential construction materials, as well as countless other commodities.

The report adds that sand extraction is severely under-regulated and many operations have a severe impact on marine, coastal, and freshwater ecosystems. Desert sand is too fine to be used in construction, which means a growing strain on coastal stocks.

Determined to find an alternative material, two civil engineering students from Melbourne’s RMIT University, Senura Kohombange and Anthony Abiad, as well as their lecturer Dr. Srikanth Venkatesan, have identified coffee grounds as an unlikely substitute.

“This project aims to replace a natural resource in concrete, sand, with coffee grounds. It can potentially help to solve two environmental issues simultaneously,” says Srikanth, Senior Lecturer of Civil and Infrastructure Engineering at RMIT.

“As well as coffee grounds going to landfill, sand is a finite natural resource. It comes from dredging our beaches and seashores which results in depletion of natural deposits. This causes significant environmental damage.”

The idea emerged when Srikanth, an avid coffee drinker, was brainstorming unorthodox methods to reduce waste. This led him to explore what uses coffee grounds had other than being sent directly to landfill.

According to a 2017 study by coffee collection and recycling initiative Reground, an estimated 2600 cafés in the City of Melbourne produce almost two million kilograms of coffee-ground waste each year. The majority of this
ends up in landfill.

Testing found up to 10 per cent of sand could safely be replaced with coffee grounds.

“We were unsure at first whether this idea could lead to anything. Very little research had been done about it. But with the guidance of Dr. Srikanth, we were able to come up with some potential designs,” Senura says.

Anthony and Senura spent several weeks in RMIT’s laboratories casting samples and conducting tests to determine the coffee-infused concrete’s strength and durability.

“As engineers, we put into application everything we learned during our studies. We used skills and knowledge acquired from specialised subjects, including non-destructive testing, durability assessments, and structural strength testing,” Senura says.

“One of the biggest challenges we faced was determining the right quantity of coffee grounds to replace sand with. Replacing too much would compromise its strength and thus, we had to develop multiple mix designs.”

Another key challenge facing the group was time. They aimed to present the project at RMIT’s annual engineering exhibition, Engenius. The industry-sponsored event provides undergraduates the opportunity to showcase projects aimed to offer an innovative solutions to real-world problems.

“We wanted to develop the project to a satisfactory level prior to presenting at Engenius on 23 October, 2019. However, we only started the semester in March and concrete needs to cure for 28 days before the final strength of the material can be assessed,” Anthony says.

“We carefully planned the stages of the project and utilised the semester break in order to meet our deadline.”

The group conducted rigorous testing in accordance to the Australian concrete standards and successfully delivered
on their goal.

“We constructed test specimens of five per cent, 10 per cent, and 20 per cent replacement of coffee grounds with sand and compared it to a normal concrete cube. These comparisons showed the allowable limits of usage, a common technique adopted in analysing the mechanical properties of concrete,” Anthony says.

“The most interesting observation was that while the use of coffee can reduce the strength of the concrete, there are ways to circumvent it.”

The team found they could replace up to 10 per cent of the sand with coffee grounds while safely preserving the concrete’s integrity. A sample “coffee brick” was created as a showpiece to present at Engenius 2019.

“As with all new ideas, some people are apprehensive about using coffee grounds in concrete. However, many were interested in our project, including people from the industry. Feedback has been really good overall. Everyone is happy that we are researching ways to improve sustainability, especially at a university level,” Anthony says.

Sustainability is a trending topic in the global coffee industry and many innovative thinkers are already recycling used coffee grounds to reduce its presence in landfill.

For example, Ford announced it is incorporating McDonald’s used coffee chaffs into car headlights, Taiwanese textile company Singtex is using recycled coffee grounds in clothing, and HuskeeCup is turning spent coffee into reusable cups.

These movements are also happening on a local scale through groups such as Melbourne-based Reground, who is converting chaffs and used coffee grounds into compost.

Senura says that civil construction needs to follow the coffee industry’s lead on transitioning towards a greener future, particularly as dependence on finite resources such as sand grows.

“The field of civil construction has not had major improvements in sustainability over the last 20 years. Construction materials have largely remained the same but the demand for infrastructure is growing,” he says.

“Materials such as concrete are vital for construction and require a large amount of manual resources such as sand and aggregate. Any research into reducing our dependency on finite natural resources would go a long way in helping reduce our impact on the environment.”

He adds that the group will continue to work on the project in hope that over time it can be adopted into mainstream construction.

“I think we have made a good start on this project. We believe this could lead to a promising product in the future. Anthony and I would like to thank RMIT University for all of its support and resources provided to us to help our project come this far, as well as Dr. Srikanth for all of his help and guidance,” Senura says.

“We would like to conduct more research into the concrete’s long-term durability aspects, perform further strength enhancements, and further develop this project. Following this, we would love to see it being used in real-world applications.”

This article appears in the February 2020 edition of BeanScene. Subscribe HERE