RMIT University engineers have converted low-grade clay into a cement supplement, opening a potential new sustainable construction materials market
RMIT University engineers have demonstrated cheaper and more abundant illite clay can be mixed with low-grade kaolinite clay, to make stronger concrete.
The study published in Construction and Building Materials 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.
According to RMIT, the global production of cement – a key ingredient in concrete – is responsible for eight per cent of global CO2 emissions.
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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, RMIT adds.
Project lead 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 can replace 20 per cent of cement usage using low-grade illite and kaolin combinations, while achieving even better performance of the yield product,”Gunasekara says.
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 per cent, with its compressive strength increased by 15 per cent, 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.