A manufacturing trial in Melbourne has produced low carbon concrete roof tiles using coal ash and glass waste, creating a lighter and more fire resistant material
The trial was carried out by the Royal Melbourne Institute of Technology(RMIT), a public research university, in partnership with Bristile Roofing, who’s manufacturing premises produced the tiles. The trial poses a solution to the pressing concern of how to handle industrial waste materials from coal-fired power stations and glass, reducing carbon footprints and offering possible engineering benefits.
The 300 low carbon concrete tiles produced were lighter and more fire resistant, while meeting Australian Standards for strength and durability. A circular life cycle assessment of the tiles demonstrated a 13% reduction in CO₂ emissions compared to conventional concrete tiles.
The tiles recycled harvested pond ash and unwashed recycled glass sand
RMIT project lead, Dr Chamila Gunasekara, said: “By replacing 10% of cement with harvested pond ash and 10% of river sand with unwashed glass waste – a total of 20% virgin material replacement – we not only reduce waste going to landfill but also produce an improved concrete product with enhanced fire resistance, a valuable feature for roofing in Australia’s climate.”
Australia produces around 12m tonnes of coal ash annually from electricity generation, with more than 400m tonnes of coal ash stored in large settling ponds. Similarly, over 1.3m tonnes of glass waste are generated each year, with more than half still ending up in landfills.
“While harvested waste pond ash is less reactive – primarily due to prolonged storage in settling ponds – it remains an attractive material due to its abundance and contribution to long-term engineering performance,” RMIT Principal Research Fellow, Dr Yulin Patrisia added.
“Despite its lower early reactivity, it helps enhance concrete performance over time. Our tests showed better dimensional stability, reduced shrinkage cracking, and continued strength gain – making it ideal for durable, non-structural applications.”
The team are now seeking to test the low carbon concrete roof tiles in real-world settings, via collaboration with local councils and commercial partners.
The low carbon concrete tiles engineering performance has been described in Sustainable Materials and Technologies, while the environmental assessment has been published in The International Journal of Life Cycle Assessment.
Low carbon concrete mixtures have other potential applications
Another of the RMIT team’s prototypes are concrete bricks using 15% harvested pond ash and 20% unwashed glass sand – totalling 35% waste materials – while satisfying Australian standards for load-bearing structural concrete and fire performance for wall elements.
Analysis found using these waste materials also improves insulation, reducing heat loss by 30% compared to conventional cement bricks.
Researchers have also developed a mixture utilising coffee grounds. The waste coffee is heated to 350°C in a low-oxygen environment, becoming a porous, charcoal-like material. This material is mixed into concrete, replacing a portion of the sand usually used in creating concrete. This method not only diverts the coffee waste from landfill, but reduces the intense demand on natural sand to meet demand for building materials.
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