Engineers at RMIT University in Australia have been able to transform low-grade clay into a high-performance cement supplement, opening a potential new market in sustainable construction materials.
While high-grade kaolin clay is best suited for cement production it's in increasingly high demand for ceramics, paints, cosmetics and paper. However, a paper published in the journal Construction and Building Materials outlines a new process where low-grade illite and kaolin clays are mixed at an equal ratio then heated at 600°C.
Co-calcination
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, 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 Dr Gunasekara.
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," Dr Gunasekara added.
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$6bn by 2032 and it's hoped, thanks to this research, a market for illite clay could follow suit.
