Common low-grade clay claimed to strengthen low-carbon concrete
Engineers at RMIT University have converted low-grade clay into what they describe as a high-performance cement supplement, opening a potential new market in sustainable construction materials.
The global production of cement – a key ingredient in concrete – is responsible for 8% of global CO₂ emissions, according to a release to industry.
Replacing some cement with clay reduces the environmental impact, but the high-grade kaolin clay best suited for cement replacement is in increasingly high demand for ceramics, paints, cosmetics and paper.
Now the RMIT team has demonstrated cheaper and more abundant illite clay can be mixed with low-grade kaolinite clay, to make stronger concrete.
The published study introduces a new process, where low-grade illite and kaolin clays are mixed at an equal ratio then heated at 600 Celsius.
Processing the two ingredients together, rather than separately, led to several improvements in the material’s performance, the study found.
Project lead Dr Chamila Gunasekara, says low-grade illite clay does not normally bind well with cement and water, but that the joint heating, or co-calcination, process greatly enhances illite clay’s binding ability, known as pozzolanic reactivity.
“Based on this approach, we are able to replace 20% of cement usage using low-grade illite and kaolin combinations, while achieving even better performance of the yield product,” says Gunasekara, from RMIT’s School of Engineering.
There was an 18% increase in the amount of disordered material in the new clays, which is beneficial for strength and durability. The material also holds more water in a chemically stable form, which points to better long-term reactions that help the structure stay strong.
“Porosity is reduced significantly by 41%, with its compressive strength increased by 15%, where changes in the way iron compounds formed help create a tighter and more compact internal structure,” Gunasekara says.
These enhancements demonstrate that the co-calcined illite-kaolin blends can match or surpass the performance of traditional kaolin-based substitutes.
Demand for kaolin is steadily growing, with the market projected to be worth US$6 billion by 2032 and its hoped, thanks to this research, a market for illite clay could follow suit.
Study lead author Dr Roshan Jayathilakage says the technique was also more energy efficient.
“Since raw materials are processed together, it streamlines industrial operations and lowers fuel use compared to multiple calcination steps,” Jayathilakage says.
“This makes the method not only technically sound but also economically and environmentally scalable.”
The research also showcases computational advancements in material science.
Underpinning the group’s work is an advanced computational tool for analysing and designing concrete, developed in partnership with Hokkaido University, Japan.
The tool allows the team to evaluate performance in various activated clays in concrete mixtures, providing detailed insights into their mechanical properties, durability and energy-efficiency, where currently available approaches had struggled.
Dr Yuguo Yu, from RMIT’s School of Engineering, says their computational tool enabled a more efficient assessment of material performance, reducing 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 says.