RMIT team replaces 80% cement with coal ash to create high performing low-carbon concrete

Engineers at RMIT University have developed a new kind of low-carbon concrete that substitutes 80% of cement with coal ash without compromising engineering performance. A waste product of coal-fired power plants, coal ash accounts for nearly 20 per cent of all waste in Australia – more than 1.2 billion tonnes of coal ash were produced in 2022 alone. Meanwhile, cement production makes up 8% of global carbon emissions and demand for concrete, which has cement as a key ingredient, is growing rapidly.

The new low-carbon concrete developed at RMIT can now recycle twice the amount of coal ash compared to current standards, cut the amount of cement required by half, and perform exceptionally well over time.

Working in partnership with AGL’s Loy Yang Power Station and the Ash Development Association of Australia, the RMIT researchers substituted 80% of the cement in concrete with coal fly ash. Existing low-carbon concretes typically have no more than 40% of their cement replaced with fly ash, explained project lead Dr Chamila Gunasekara from RMIT’s School of Engineering.

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

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 underutilised resource for cement replacement,” Gunasekara said.
“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.”

A pilot computer modelling program developed by RMIT in partnership with Hokkaido University’s Dr Yogarajah Elakneswaran has been used to forecast the time-dependent performance of these new concrete mixtures.

“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,” Dr Yuguo Yu, an expert in virtual computational mechanics at RMIT, explained.

Published recently in the prestigious journal Cement and Concrete Research, this pioneering approach reveals how various ingredients in the new low-carbon concrete interact over time. With its wide applicability to various materials, it also marks a crucial stride towards digitally assisted simulation in infrastructure design and construction.

Relevant studies
‘Unified hydration model for multi-blend fly ash cementitious systems of wide-range replacement rates’ is published in Cement and Concrete Research (DOI: 10.1016/j.cemconres.2024.107487)
‘Sulphate and acid resistance of HVFA concrete incorporating nano silica’ is published in Construction and Building Materials (DOI: 10.1016/j.conbuildmat.2023.132004)
‘Long term mechanical performance of nano-engineered high volume fly ash concrete’ is published in Journal of Building Engineering (DOI: 10.1016/j.jobe.2021.103168)