Novel concrete reduces impact of both coal ash and cement

The coal ash produced by coal-fired power plants in Australia accounts for nearly a fifth of the nation’s waste and will remain abundant for decades to come, even with the transition to renewables. More than 1.2 billion tonnes of coal ash were produced by coal-fired power plants in 2022.

The production of cement, which uses some coal ash as an ingredient, makes up 8% of global carbon emissions. Demand for concrete — of which cement is a key component — is growing rapidly.

Researchers at RMIT might have now found a solution to both problems, with the development of a low-carbon concrete that can recycle double the amount of coal ash compared to current standards, halve the amount of cement required and perform well over time.

The RMIT team: Dr Yuguo Yu, Professor Sujeeva Setunge, Dr Dilan Robert, Dr Chamila Gunasekara and Dr David Law. Image credit: Michael Quin, RMIT.

The engineers at RMIT 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. RMIT project lead Dr Chamila Gunasekara said this represents 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,” said Gunasekara, from RMIT’s School of Engineering.

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 underutilised resource for cement replacement,” Gunasekara said, adding that there are hundreds of megatonnes of ash waste 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,” he said.

New modelling technology shows low-carbon concrete’s long-term resilience

In addition to creating the novel concrete, RMIT has developed a pilot computer-modelling program in partnership with Hokkaido University’s Dr Yogarajah Elakneswaran that can forecast how the new concrete mixtures will perform over time.

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

“The inclusion of ultrafine nano additives significantly enhances the material by increasing density and compactness.”

This modelling, with its applicability to various materials, marks a critical step towards digitally assisted simulation in infrastructure design and construction. The team aims to use the technology to instil confidence among local councils and communities in adopting novel low-carbon concrete for various applications.

The team’s work has most recently been published in the journal Cement and Concrete Research.

Top image: Dr Chamila Gunasekara holds a sample of the low-carbon concrete. Image credit: Michael Quin, RMIT.