Low-carbon concrete helps clean up coal ash deposits

Man standing outdoors holds pillar of concrete made from coal fly ash
RMIT project lead Dr Chamila Gunasekara

Engineers at RMIT have partnered with AGL‘s Loy Yang Power Station and the Ash Development Association of Australia to substitute 80% of the cement in concrete with coal fly ash.

New modelling reveals that low-carbon concrete developed at RMIT University can recycle double the amount of coal ash compared to current standards, halve the amount of cement required and perform exceptionally well over time.

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More than 1.2 billion tonnes of coal ash were produced by coal-fired power plants in 2022. In Australia, it accounts for nearly a fifth of all waste and will remain abundant for decades to come, even as we shift to renewables.

Meanwhile, cement production makes up 8% of global carbon emissions and demand for concrete—which uses cement as a key ingredient—is growing rapidly.

RMIT project lead Dr Chamila Gunasekara said this represented a significant advance as existing low-carbon concretes typically have no more than 40% of their cement replaced with fly ash.

“Our addition of nano additives to modify the concrete’s chemistry allows more fly ash to be added without compromising engineering performance,” Dr Gunasekara said.

Comprehensive lab studies have shown the team’s approach is also capable of harvesting and repurposing lower grade and underutilised ‘pond ash’—taken from coal slurry storage ponds at power plants—with minimal pre-processing.

Large concrete beam prototypes have been created using both fly ash and pond ash and shown to meet Australian Standards for engineering performance and environmental requirements.

“It’s exciting that preliminary results show similar performance with lower-grade pond ash, potentially opening a whole new hugely under-utilised resource for cement replacement,” Dr Gunasekara said.

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“Compared to fly ash, pond ash is underexploited in construction due to its different characteristics. There are hundreds of megatonnes of ash wastes sitting in dams around Australia, and much more globally.”

“These ash ponds risk becoming an environmental hazard, and the ability to repurpose this ash in construction materials at scale would be a massive win.”

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