Low-grade clay turned into powerful cement for green construction

The illite clay, when blended with low-grade kaolinite, can yield stronger concrete.

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Mrigakshi Dixit

The combined clay mix after being heat treated, ready for use as a cement supplement.

RMIT

Concrete builds our world, but its core ingredient, cement, comes with a heavy environmental cost. It’s responsible for a total of 8% of global CO₂ emissions.

The industry is actively researching and implementing various strategies to reduce its carbon footprint.

Engineers have long recognized that swapping out some cement for clay can drastically cut environmental impact.

The go-to solution has been high-grade kaolin clay. But there’s a problem: kaolin’s high demand in industries like ceramics and cosmetics makes it increasingly scarce and pricey for construction.

Now, new research from RMIT University in Australia has unlocked the potential of low-grade illite clay, a cheaper and far more abundant alternative.

A key insight is that this illite clay, when blended with low-grade kaolinite, can yield stronger concrete.

A large chunk of cement’s CO₂ emissions result from a chemical reaction where limestone (CaCO₃) is heated in a kiln, breaking down into lime (CaO) and releasing CO₂. This process is an unavoidable step in creating cement clinker.

In this new method, low-grade illite and kaolin clays are mixed in equal parts and then heated together at 600 degrees Celsius.

This “co-calcination” process significantly improves illite clay’s ability to bind with cement and water, a property called pozzolanic reactivity, even though it doesn’t normally do so.

“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,” expressed Dr. Chamila Gunasekara, from RMIT’s School of Engineering.

This joint heating process, or co-calcination, isn’t just about mixing. It leads to major changes in the material’s performance, which are important for strength and durability.

What’s more, the material chemically locks in more water, ensuring improved long-term reactions for enhanced structural integrity.

It leads to a 41% reduction in porosity and a 15% increase in compressive strength, making concrete even stronger.

The team says this development is economically and environmentally transformative.

High-grade kaolin is projected to be a 6-billion-dollar market by 2032. Thanks to this research, a whole new market for abundant illite clay could emerge.

“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,” said Dr Roshan Jayathilakage, study lead author.

Adding another layer to this development is RMIT’s advanced computational tool, developed in partnership with Hokkaido University. This virtual tool dramatically speeds up material assessment, thereby reducing the need for lab tests.

“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,” stated Dr Yuguo Yu from RMIT.

“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,” Yu added.

This research paves the way for a low-carbon future, making sustainable construction a reality.

The research and development in sustainable construction is actively happening.

Recently, Montana State University researchers engineered a living building material made from fungal mycelium and bacterial cells.

Interestingly, this innovative bio-composite can self-repair and remain viable for weeks, paving the way for a new era of regenerative architecture. The material’s low-temperature production and reliance on living cells offer a promising solution to reduce the construction industry’s environmental impact.

The findings were published in Construction and Building Materials

Mrigakshi Dixit Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her work has been featured in well-known publications including Nature India, Supercluster, The Weather Channel and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.

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