A team of researchers from RMIT have developed low-carbon concrete which recycles double the coal ash, and halves cement use. This development could be used to address coal waste and high cement production emissions in industry. Manufacturers’ Monthly reports.
Researchers at RMIT University have developed a low-carbon concrete that has demonstrated the potential to significantly enhance recycling and sustainability in construction.
This new concrete can recycle double the amount of coal ash compared to current standards, halve the cement needed, and maintain exceptional long-term performance.
With over 1.2 billion tonnes of coal ash produced annually, this innovation addresses the substantial environmental impact of coal waste and the high carbon emissions from cement production, which constitutes 8 per cent of global emissions.
“Our research aims to make a vital contribution to Australia’s net-zero emission targets and pave the way for a new generation of infrastructure construction, both in Australia and internationally,” said RMIT project lead Dr Chamila Gunasekara, from RMIT’s School of Engineering.
The research team
The project commenced in 2016 when – after completing his PhD – Gunasekara began developing methods to produce low-carbon concrete alongside a team of researchers.
The team recognised the necessity to address sustainability concerns in construction, and thus, aimed to address it with low-carbon concrete.
“The challenge lies in clinker production, a crucial step in cement manufacturing, where CO2 reduction has already been optimised,” said Gunasekara.
“While further reductions are difficult to achieve, there’s a promising aspect in the emergence of alternative sustainable materials.
“However, for these materials to be viable, they must be readily available with a robust supply chain.”
Gunasekara explained that with the increasing adoption of renewable energy sources, traditional power stations are expected to persist for the next decade, resulting in an accumulation of underutilised resources such as fly ash for years to come.
Dr Chamila Gunasekara, Dr David Law. Image: Michael Quin/RMIT
“Fortunately, there are ample such materials in Australia and many other countries. Take fly ash, for instance, which is abundantly available,” he said.
“Despite the shift towards renewables, traditional power stations are unlikely to disappear in the next decade, leaving us with decades’ worth of underutilised materials like fly ash.”
With key contributions from Dr. Yuguo Yu, the team developed a predictive model for the concrete’s long-term performance.
Yu highlights a persistent challenge in the field: predicting the long-term durability of newly developed materials.
“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,” he said.
Professor Sujeeva Setunge coordinated the research through the ARC Industrial Transformation Research Hub for Transformation of Reclaimed Waste Resources to Engineered Materials and Solutions for a Circular Economy (TREMS).
Dr. Dilan Robert and Dr. David Law were also key members of the team, partnering with AGL’s Loy Yang Power Station and the Ash Development Association of Australia.
Additionally, Hokkaido University’s Dr. Yogarajah Elakneswaran contributed to developing a computer modelling program to optimise the concrete mix.
This enabled the team to forecast the new concrete’s long-term performance – their goal; to reduce cement usage and address environmental waste challenges, whilst also promoting sustainable construction practices.
Materials science and concrete
Throughout history, coal fly ash has been utilised in cement manufacturing as a valuable supplementary cementitious material.
Dating back several decades, its usage in the construction industry has been prevalent.
Fly ash, a byproduct of coal combustion, gained prominence due to its pozzolanic properties, which enhance the durability and strength of concrete when used as a partial replacement for cement.
Since its initial discovery as a beneficial material, fly ash has been integrated into cement formulations worldwide.
Over time, research and innovation have led to a deeper understanding of its properties and potential applications, driving its widespread adoption in the construction sector.
As environmental concerns grew and the demand for sustainable building practices intensified, the use of fly ash as a cement alternative gained even more prominence.
Cement production is a major source of carbon dioxide (CO2) emissions, primarily due to the calcination process, where limestone (calcium carbonate) is heated to produce lime (calcium oxide), releasing CO2 in the process.
Additionally, fossil fuels such as coal, oil, and natural gas are often used as energy sources in cement kilns, further contributing to carbon emissions.
Cement manufacturing is energy-intensive, requiring large amounts of energy for the high-temperature calcination process and for grinding raw materials into cement clinker.
This reliance on fossil fuels and electricity from non-renewable sources contributes to greenhouse gas emissions and exacerbates climate change.
The RMIT team has since demonstrated methods to substitute up-to 80 per cent of the cement in concrete with coal fly ash, surpassing the typical 40 per cent replacement in existing low-carbon concretes.
“Our addition of nano additives to modify the concrete’s chemistry allows more fly ash to be added without compromising engineering performance,” said Gunasekara.
“We doubled the current cement reduction in concrete, which necessitated modifications to the cement chemistry, especially with the introduction of nano additives for optimal performance.
“Our research entailed considerable time and effort in refining the cement chemistry to accommodate this doubled waste inclusion in concrete.”
The team has demonstrated that lower-grade pond ash from coal slurry storage ponds can also be repurposed effectively.
Prototypes using both fly ash and pond ash meet Australian engineering and environmental standards, potentially repurposing a vast, underutilised resource.
“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 megatons 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.”
This physics-based model enables the optimisation of concrete mixes by understanding ingredient interactions over time, enhancing material density and compactness with nano additives.
“We are currently conducting a full lifecycle assessment to understand the environmental impact of this concrete, from raw material production to end of life,” said Gunasekara.
“The structural capacity and durability of this new concrete are comparable to conventional concrete. This innovation can reduce CO2 emissions by 10 to 20 per cent, which is a significant achievement.”
“After developing these mix proportions, matching the chemistry and other factors, the next step was to test the short-term and long-term performance.
“We need to meet all specifications and standards, including Australian Standards, to satisfy engineering and environmental requirements.”
The road to commercialisation
Gunasekra said that another priority moving forward, is to achieve commercialisation of their low-carbon concrete.
“We have spent a considerable amount of time balancing the chemistry and developing our mixed proportion technology, supported by extensive simulation and physics-based modelling,” he said.
“The technology we’ve developed is not limited to this research and is now ready for commercial trials and commercialisation.
“The concepts and technologies from our experiments and numerical modelling can be extended to other materials.”
Gunasekara continued to explain that their concrete is a significant achievement, and that it’s commercialisation ultimately depends on its reception from end-users and testing.
“As scientists and researchers, we rely on end users to help us commercialise this technology, as universities alone do not have that capacity,” he said.
“The next phase involves conducting short-term and long-term performance testing on our concrete mix proportions.
“We aim to ensure compliance with Australian Standards and other relevant specifications, meeting both engineering performance and environmental requirements.
“Presently, we’re collaborating with ready-mix concrete companies, such as Malai Borel Hall.”
The RMIT team are also working with local councils across Australia that are actively enabling the development of the project.
“We’ve garnered partnerships with nearly 10 councils who align with our research hub,” said Gunasekara.
“With abundant resources at our disposal, we’re actively collaborating with local councils to deploy our concrete innovations.
Gunasekara expressed that RMIT’s new concrete will eventually be utilised in various industries.
“These advancements can be integrated into a range of construction projects,” he said.
“This includes footpaths, structural elements in residential buildings, and extending to critical infrastructure like rural bridges and roads.”
Gunasekara said that their concrete can be equally scaled compared to conventional concrete.
“This can be scaled up from small-scale to a larger scale,” he said.
“We can produce it in a normal batching plant without needing any additional sophisticated production lines.
Gunasekara said that just one silo is needed to store the materials, and then RMIT can use a normal mixing process, like any generic manufacturing process.
“We can take advantage of existing batching plants,” he said.
“Performance-wise, it is comparable to conventional concrete, and the materials are readily available in Australia.”
