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RMIT University reported in May 2024 that its researchers developed a concrete formulation replacing 80% of the cement with coal fly ash. That figure is a share of the cement being replaced—not a claim that 80% of the entire concrete mix is ash. The approach combines high-volume fly ash with nano additives, and RMIT says prototype beams met Australian engineering-performance and environmental requirements. The report describes modelling and prototype testing, not decades of proven field service.
What RMIT reported
In a report published on 16 May 2024, RMIT said its engineers worked with AGL’s Loy Yang Power Station and the Ash Development Association of Australia on low-carbon concrete with 80% cement replacement by coal fly ash. RMIT characterized existing low-carbon concretes as typically replacing no more than 40% of cement with fly ash. These percentages refer to cement replacement, not the proportion of the whole concrete mix.
The project addresses two linked issues: cement production is responsible for about 8% of global carbon emissions, according to RMIT’s report, while coal-fired power plants produced more than 1.2 billion tonnes of coal ash in 2022, also as reported by RMIT. Reusing ash could reduce demand for cement and give a byproduct another use, but the report does not provide a lifecycle assessment quantifying the project mix’s net emissions reduction.
How the high-ash formulation is intended to work
Fly ash reacts more slowly than cement, which can complicate early performance when it replaces a large share of cement. RMIT says the formulation uses nano additives to modify the concrete’s chemistry and support engineering performance. Dr Chamila Gunasekara of RMIT’s School of Engineering said: “Our addition of nano additives to modify the concrete’s chemistry allows more fly ash to be added without compromising engineering performance.”
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RMIT also said the ultra-fine additives increase density and compactness: “The inclusion of ultra-fine nano additives significantly enhances the material by increasing density and compactness.” These statements explain the intended role of the additives; the university news report does not publish a mix recipe, dosage, or detailed test results that would allow readers to reproduce the formulation.
What the prototype results establish—and what they do not
RMIT reported that large beam prototypes made with fly ash and pond ash met Australian Standards for engineering performance and environmental requirements. The news report does not name the specific standards, provide test tables, or state the full testing conditions. The standards claim should therefore be understood as RMIT’s reported result, not as a separately verified certification or a specification for a commercially available product.
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RMIT also described a physics-based modelling program developed with Dr Yogarajah Elakneswaran of Hokkaido University to forecast time-dependent behaviour and help optimise mixes. RMIT’s Dr Yuguo Yu said: “We’ve now created a physics-based model to predict how the low-carbon concrete will perform over time, which offers us opportunities to reverse engineer and optimise mixes from numerical insights.” A model can inform design and predict behaviour; it is not equivalent to decades of exposure data. The May 2024 report does not establish a quantified service life or long-term field performance.
Pond ash is a separate, preliminary part of the work
Coal fly ash and pond ash are not interchangeable labels. Pond ash is lower-grade ash stored in coal slurry ponds and can have different material characteristics from ash collected directly from power-plant processes. RMIT said it was exploring the use of pond ash with minimal pre-processing and described its potential for similar performance as preliminary. That is not evidence that pond ash has already been validated at scale for general construction use.
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How other high-fly-ash studies compare
Other studies show that high replacement rates can work in particular laboratory or engineered systems, but their results cannot be transferred to RMIT’s mix. Ash source and quality, other binder ingredients, water-to-binder ratio, curing, specimen type, test age, and durability exposure all affect comparisons.
| Study | Formulation and reported result | How to interpret it |
|---|---|---|
| RMIT project, reported May 2024 | 80% cement replacement with coal fly ash; RMIT also reported beam prototypes using fly ash and pond ash met Australian engineering-performance and environmental requirements. | The university report does not name the standards or publish detailed test tables. Pond-ash performance was described as preliminary. |
| Jing Yu, Gengying Li, and Christopher K.Y. Leung, 2018 | A mortar with 80% fly-ash replacement exceeded 65 MPa compressive strength at 28 days and had 70% lower total hydration heat than conventional cement mortar under that study’s conditions. | These measurements belong to that study’s mortar, not to RMIT’s concrete formulation. |
| Results in Engineering study, 2023 | In a Vietnam high-strength concrete study, the 30% fly-ash samples had the best mechanical and durability properties among the samples tested. | The result illustrates that a higher replacement percentage is not automatically a better-performing mix. |
| Suliman Khan, Safat Al-Deen, and Chi King Lee, 2026 | A different ternary-blend study evaluated mixes with 80%, 85%, and 90% ordinary Portland cement replacement for durability through one year. | These are separate formulations and results, not RMIT findings or proof of multi-decade service. |
| Yangjie Chen et al., 2026 | A separate high-performance study reported mixes with 60–80% fly ash and its own freeze-thaw and emissions results. | Those results apply only to that study’s formulations and test conditions. |
What builders and specifiers should check
The RMIT report is a promising research announcement, not a complete construction specification. Anyone assessing a high-volume fly-ash concrete for a project would need mix-specific evidence and approval for the intended use. Useful points to verify include:
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- Ash source and quality: confirm whether the material is fly ash or pond ash and obtain its relevant characterization and quality-control information.
- Binder composition: identify the replacement basis and any slag, silica fume, lime, nanosilica, or other additives in the binder.
- Mix and curing: review the water-to-binder ratio, curing regime, and expected early-age performance.
- Performance evidence: match strength results to the test age and specimen type, and assess durability under exposures relevant to the project.
- Compliance and carbon: confirm applicable local standards and compare lifecycle carbon using a stated method and project-specific inputs.
Sources
- RMIT University, “Low-carbon concrete built to last,” 16 May 2024
- “Unified hydration model for multi-blend fly ash cementitious systems of wide-range replacement rates,” Cement and Concrete Research, 2024
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