RMIT University engineers have converted low-grade clay into 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 eight per cent of global CO₂ emissions.
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 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.
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Project lead Dr Chamila Gunasekara, said 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 per cent of cement usage using low-grade illite and kaolin combinations, while achieving even better performance of the yield product,” said Gunasekara, from RMIT’s School of Engineering.
There was an 18 per cent 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 said.