Australia’s push toward lower carbon construction has taken an unexpected turn. Researchers at RMIT University have shown that spent coffee grounds, one of the country’s largest organic waste streams, can be turned into a functional ingredient for concrete that is both stronger and significantly lower in embodied carbon.
The findings come from a new peer-reviewed study published in the International Journal of Construction Management titled Carbon footprint reduction in concrete using spent coffee grounds biochar. A life cycle perspective.
For builders, engineers and suppliers searching for credible sustainability pathways that do not add complexity or cost, this research points to a potential breakthrough.
Why Coffee Waste Matters
Australians generate roughly 75,000 tonnes of used coffee grounds every year. Most ends up in landfill where it contributes to methane emissions. At the same time, the construction industry faces mounting pressure on natural sand supplies, rising materials costs and tightening carbon reporting requirements.
Turning a freely available waste product into a performance-enhancing concrete ingredient checks several boxes. It reduces organic waste going to landfill. It relieves pressure on increasingly scarce sand resources. And it cuts embodied carbon at a time when the industry is preparing for more stringent sustainability expectations.
From Café Bins to Building Materials
Earlier RMIT trials showed that heating used coffee grounds at around 350 degrees Celsius without oxygen produces a stable biochar that can replace a portion of sand in concrete mixes.
Replacing 15 percent of sand with coffee biochar increased 28-day compressive strength by about 30 percent. That trial, conducted under controlled laboratory conditions, suggested a viable performance pathway but did not yet answer the key question industry always asks: What does this do to whole-of-life impacts and emissions?
The latest study provides the missing data.
What the New Life Cycle Analysis Found
Led by Dr Jingxuan Zhang and Dr Mohammad Saberian from RMIT’s School of Engineering, the research team assessed the environmental impact of biochar concrete from production through to end of life.
The results are significant.
Carbon footprint reduction compared with traditional concrete.
• 5 percent biochar content. 15 percent lower carbon dioxide emissions
• 10 percent biochar content. 23 percent lower carbon dioxide emissions
• 15 percent biochar content. 26 percent lower carbon dioxide emissions
The study also recorded:
• up to 31 percent lower fossil fuel consumption across the life cycle
• reduced impacts on rivers and lakes
• no additional negative environmental burdens across the assessed categories
The findings confirm what the original strength tests hinted at. Moderate volumes of coffee biochar not only enhance structural performance but materially reduce environmental impacts.
Why It Works
Coffee grounds have a porous internal structure that becomes even more open during the low-oxygen heating process. This creates a lightweight, high-surface-area material that bonds well within cementitious mixes.
Where traditional sand provides density and stability, biochar introduces a different functional role. It improves the internal matrix of the concrete, helping distribute loads more effectively while maintaining workability.
Most importantly, it substitutes natural sand, a resource under increasing environmental and regulatory pressure globally.
Industry Demand Is Increasing
The construction sector is accelerating its search for circular and lower impact materials. Builders are already being asked about carbon transparency from clients, financiers and government bodies.
For civil projects, sand scarcity and cost escalation remain ongoing challenges. Recycled content in public infrastructure is becoming mandatory across multiple states.
Solutions that replace conventional materials without needing major process changes are rare. This is what gives coffee biochar its potential.
Dr Zhang says the findings provide a strong foundation for commercial testing.
“We showed that coffee biochar can cut concrete’s carbon footprint in the scenarios we assessed, while earlier trials demonstrated strength gains using the same approach,” she said.
Professor Chun Qing Li, who supported the research, highlighted the practicality of the innovation.
“Using moderate amounts of coffee biochar offers a clear, measurable pathway to lower impact concrete,” he said.
More Than Theory. Real Projects Are Already Underway
This research has not been confined to the lab.
RMIT and industry partners have already tested the material in the field, including:
• a public footpath pilot in Gisborne, Victoria
• a concrete section within the Victorian Big Build program
• an installation showcased in the National Gallery of Victoria’s Making Good exhibition
• collaborations with BildGroup during major road upgrade works
These trials help validate the on-site handling, performance and curing characteristics under typical construction conditions.
Dr Saberian says demand from industry and local government is growing.
“Next steps include larger pilots, mix optimisation and alignment with standards so projects can adopt this confidently,” he said.
The research team is now engaging with councils, suppliers and contractors to explore supply chain development, including the consistent collection and processing of spent coffee grounds.
The Circular Economy in Action
Australia’s transition to a circular economy by 2030 emphasises the reuse of waste streams across manufacturing and construction.
Coffee biochar concrete supports this target by:
• diverting organic waste from landfill
• reducing the need for natural sand extraction
• lowering embodied carbon across the mix
• demonstrating public engagement with waste-to-resource initiatives
• providing a repeatable, scalable model for other organic waste materials
For builders, this aligns with rising community expectations around sustainability and responsible material selection.
Where the Potential Goes Next
While the study shows strong early promise, several steps remain before coffee biochar concrete becomes mainstream.
Key areas of ongoing work include:
• optimisation of mix designs for various applications
• alignment with Australian Standards for concrete
• expansion of pilot programs in civil and residential projects
• development of large scale, consistent biochar supply
• testing under diverse structural, durability and environmental conditions
However, the building blocks are now in place. The research demonstrates that replacing a portion of sand with coffee biochar offers both carbon and performance benefits, underpinned by credible life cycle analysis.
Why Builders Should Pay Attention
This is not just a lab curiosity. It sits within a broader global movement toward alternative binders, recycled aggregates and low-carbon material substitutes.
For Australian builders, the implications are practical.
What this could mean in the future.
• stronger, lighter composites with reduced environmental impact
• lower embodied carbon pathways for residential slabs and footpaths
• new procurement models incorporating recycled materials
• opportunities to partner with local councils on circular economy initiatives
• reduced reliance on quarry sand as resources tighten
These results are promising enough that every builder, supplier, engineering firm and council should be watching the next phase.
It is not often that a waste material we throw away daily can help produce stronger, lower carbon infrastructure at scale.
But that is exactly what this research suggests.
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