Engineers at RMIT University have achieved a breakthrough in sustainable construction materials by transforming low-grade clay into a high-performance cement supplement, potentially opening a new market for eco-friendly building products.

Cement production, a central component of concrete, is responsible for about 8 per cent of global CO₂ emissions, making the search for greener alternatives a pressing concern for the industry.

Traditionally, high-grade kaolin clay has been used to partially replace cement in concrete, reducing environmental impact.

However, kaolin is in growing demand for ceramics, paints, cosmetics, and paper, limiting its availability for construction.

The RMIT team has now demonstrated that more abundant, lower-cost illite clay, when mixed with low-grade kaolinite clay and processed together, can serve as a superior cement substitute.

The study, published in Construction and Building Materials, details a new process in which illite and kaolin clays are blended in equal parts and heated to 600 degrees Celsius.

This joint heating, known as co-calcination, significantly enhances the binding ability — or pozzolanic reactivity — of illite clay, which on its own does not bind well with cement and water.

Project lead Dr Chamila Gunasekara explained: “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.”

The research found that the co-calcined clay blend increased the proportion of disordered material by 18 per cent, a change that boosts strength and durability.

The new material also retains more water in a chemically stable form, supporting longer-term structural integrity.

“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.

These performance gains mean the illite-kaolin blend can match or exceed traditional kaolin-based cement substitutes.

With global demand for kaolin projected to reach US$6 billion by 2032, researchers hope this innovation will spur the development of a new market for illite clay.

The process also offers industrial and environmental benefits.

Study lead author Dr Roshan Jayathilakage noted: “Since raw materials are processed together, it streamlines industrial operations and lowers fuel use compared to multiple calcination steps.

“This makes the method not only technically sound but also economically and environmentally scalable.”

Supporting this work is a new computational tool, developed in partnership with Hokkaido University, Japan, that allows for advanced analysis and design of concrete mixtures.

Dr Yuguo Yu from RMIT’s School of Engineering said: “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.

“This virtual tool could enable the construction industry to accelerate the adoption of eco-friendly materials, paving the way of greener transformation for a more sustainable future.”

The research is part of 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 expertise from nine Australian universities and 36 industry and international partners to minimise waste and repurpose reclaimed materials for construction and advanced manufacturing.

The full study, A combination technique to improve natural low-grade illite as supplementary cementitious material for concrete, is published in Construction and Building Materials.