Engineers at RMIT University 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 8% 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 team 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.
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% of cement usage using low-grade illite and kaolin combinations, while achieving even better performance of the yield product,” Gunasekara said.
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 said 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 said.
“This makes the method not only technically sound but also economically and environmentally scalable.”
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.
This research was enabled by the ARC Industrial Transformation Research Hub for Transformation of Reclaimed Waste Resources to Engineered Materials and Solutions for a Circular Economy (TREMS).
Led by RMIT’s Professor Sujeeva Setunge, TREMS brings together top scientists and industry experts from nine Australian universities and 36 state, industry, and international partners to minimise waste and repurpose reclaimed materials for construction and advanced manufacturing.