Engineers at RMIT University have discovered a new way to convert low-grade clay into high-performance cement.
The global production of cement – a key ingredient in concrete – is reportedly responsible for 8 percent of global CO2 emissions.
Replacing some cement with clay reduces its environmental impact. However, the high-grade kaolin clay best suited for cement replacement is already in high demand for ceramics, paints, cosmetics and paper, leaving a reduced quantity available for cement production.
To address this, the RMIT team has now demonstrated that cheaper and more abundant illite clay can be mixed with low-grade kaolinite clay to make stronger, more sustainable concrete.
A low-carbon future
Low-grade illite and kaolin clays are mixed at an equal ratio and then heated at 600 degrees Celsius.
Processing the two ingredients together, rather than separately, led to improvements in the material’s performance.
Project lead Dr Chamila Gunasekara from RMIT’s School of Engineering said low-grade illite clay does not normally bind well with cement and water.
However, the joint heating, or co-calcination, process significantly enhances illite clay’s binding ability, known as pozzolanic reactivity.
“Based on this approach, we are able to replace 20 percent of cement usage using low-grade illite and kaolin combinations, while achieving even better performance of the yield product,” Gunasekara said.
There was a reported 18 percent increase in the amount of disordered material in the new clays, which is beneficial for strength and durability.
The new material also holds more water in a chemically stable form, which indicates better long-term reactions that help the structure stay strong.
“Porosity is reduced significantly by 41 percent, with its compressive strength increased by 15 percent, where changes in the way iron compounds are formed help create a tighter and more compact internal structure,” Gunasekara added.
The findings of this study, published in Construction and Building Materials, demonstrate that the co-calcined illite-kaolin blends can match or surpass the performance of traditional kaolin-based substitutes.
Demand for kaolin is growing, with the market projected to be worth $6 billion by 2032.
“Since raw materials are processed together, it streamlines industrial operations and lowers fuel use compared to multiple calcination steps,” study lead author Dr Roshan Jayathilakage said.
“This makes the method not only technically sound but also economically and environmentally scalable.”
Technological advancements in material science
The research also demonstrated computational advancements in material science.
The team relied on an advanced computational tool for analysing and designing concrete, developed in partnership with Japan’s Hokkaido University.
It provided detailed insights into the material’s mechanical properties, durability and energy efficiency.
Dr Yuguo Yu, from RMIT’s School of Engineering, said that apart from enabling a more efficient assessment of material performance, it also reduced the reliance on extensive laboratory tests.
“By predicting how different clay compositions affect concrete behaviour, engineers are able to better design energy-efficient mixtures tailored for local clay types and specific environmental conditions,” he said.
RMIT is also collaborating with other international partners, including the European Synchrotron Radiation Facility (ESRF) in France. Jointly, the teams are continuing to investigate how different clay types and activation techniques influence concrete behaviour at multiple scales, while expanding performance testing in real-world conditions.
Image: Supplied
New sustainable concrete material uses treated water sludge.
