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Concrete reinforced with processed coffee waste has moved from the laboratory into Australian footpaths, but the field trial did not reproduce the headline laboratory strength gain. In a 2025 study of a Gisborne, Victoria, trial, the coffee-biochar mix had lower compressive strength than the control at seven and 28 days, but higher 28-day flexural strength. The roughly 30% compressive-strength increase applies to a specific laboratory mix using biochar made at 350 °C—not to the field mix or to concrete made with ordinary coffee grounds.
What “coffee concrete” actually contains
It does not contain brewed coffee or raw spent grounds. Raw coffee grounds are organic material that can decompose and weaken concrete. RMIT researchers instead heat spent grounds without oxygen to make biochar, then use that processed material as a partial replacement for fine aggregate such as sand. The research programme has also examined biochar made from wood chips. RMIT describes the approach as a way to turn a waste stream into a possible partial substitute for a construction material.
The distinction matters: performance depends on the biochar’s production and moisture characteristics, the replacement level, and the concrete mix design. Coffee grounds cannot simply be tipped into a standard mix and expected to deliver the reported results.
How the laboratory result differs from the footpath trial
The headline strength result came from laboratory work using coffee-ground biochar produced at 350 °C. In that tested mix, the researchers reported about 30% higher 28-day compressive strength than the comparison mix. That result is specific to the experimental processing temperature, replacement level, materials and mix; it is not a general guarantee for coffee-biochar concrete. The peer-reviewed field study summarizes this laboratory finding alongside its real-world evaluation: Roychand and co-authors, 2025.
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For the Gisborne trial, the supplier’s continuous pyrolysis equipment could not operate at the requested 350 °C, so it produced the biochar at 450 °C. That production constraint changed the material used in the field mix. The lab and field results therefore should not be treated as a direct repeat of the same recipe.
What the Gisborne footpath tests found
RMIT and Macedon Ranges Shire Council laid trial sections in Gisborne, Victoria: a standard-concrete control, a coffee-biochar mix and a wood-chip-biochar mix. Researchers assessed slump, compressive strength, flexural strength and shrinkage, with testing conducted by an independent National Association of Testing Authorities-accredited laboratory. The published results for the coffee-biochar mix, compared with the control, were:
| Test | Reported field-trial result |
|---|---|
| Compressive strength at 7 days | About 6% lower than the control |
| Compressive strength at 28 days | 9.3% lower than the control |
| Flexural strength at 28 days | 18.9% higher than the control |
The authors also reported improved shrinkage behaviour and continued strength development in later core samples. Those findings do not erase the lower compressive-strength measurements at the reported seven- and 28-day ages, nor do they turn the field result into confirmation of the laboratory’s roughly 30% gain.
Why processing and moisture matter
The field biochar was water-quenched and carried substantial moisture; the team accounted for that water in the concrete mix. The authors discuss moisture saturation and internal curing as possible contributors to field performance. These details help explain why biochar production and material condition are part of the engineering, rather than incidental preparation steps.
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- High tensile strength; Above all other conventional reinforcements
- Smooth blending; Does not clump or ball during mixing like many pva and poly fibers
- Corrosion resistant; Will not decay or rust over time, unlike traditional steel
- Frost and heat resistant; Takes freeze thaw cycles in stride
- Moisture resistant; Weathers the wettest environments with built in alkali resistance
From a trial path to an infrastructure project
In October 2024, RMIT reported that coffee-biochar concrete had been used in a 30-cubic-metre footpath along McGregor Road in Pakenham, Victoria, as part of the Pakenham Roads Upgrade. For that project, Earth Systems converted five tonnes of spent coffee grounds—described by RMIT as about 140,000 coffees’ worth—into two tonnes of biochar. RMIT called it the first coffee-concrete section in a Victorian Big Build project. The university’s project account reports those quantities and context.
Deployment in a project is evidence that the material has been used beyond a laboratory, not proof that it is already a widely available or standardized product. RMIT’s February 2025 update named project partners and supporters and said commercialisation work was underway. Its November 2025 account described larger pilots, mix optimisation and alignment with standards as next steps. RMIT’s update on the life-cycle study and development path frames the work as ongoing.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the environmental figures do—and do not—show
RMIT’s 2025 summary of a life-cycle assessment reports modeled carbon-dioxide reductions of 15%, 23% and 26% in scenarios replacing 5%, 10% and 15% of sand with coffee biochar, respectively, and up to 31% lower fossil-fuel use. These are modeled outcomes for the assessed scenarios, not measured emissions savings from the Gisborne footpath. The figures should not be compared directly with strength-test percentages: one set comes from life-cycle modeling, the other from concrete tests.
RMIT has also estimated that Australia generates about 75 million kilograms of spent coffee grounds annually, which could replace up to 655 million kilograms of sand; its global estimates are 10 billion kilograms of grounds and potential replacement of up to 90 billion kilograms of sand. These are university estimates of possible scale, not quantities already diverted or used in concrete. RMIT’s 2024 account gives the waste and potential replacement estimates.
What builders should take away
- The material is engineered biochar, not raw coffee waste. Processing and mix design are prerequisites for meaningful performance results.
- Strength depends on the specific mix and test. The 350 °C laboratory mix showed about 30% higher 28-day compressive strength, while the 450 °C Gisborne field mix tested below its control in compressive strength at seven and 28 days and above it in 28-day flexural strength.
- Field use is real, but the evidence does not establish a general-purpose product. A later Pakenham infrastructure footpath demonstrates project use; larger pilots, optimisation and standards alignment remain part of the development path.
- Environmental benefits are promising but modeled. The reported carbon and fuel-use reductions apply to life-cycle scenarios, not direct measurement of the Gisborne installation.
For contractors and specifiers, this is a materials-development story rather than a consumer how-to: reproducing the research requires controlled biochar feedstock and processing, an engineered concrete mix and suitable testing.
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