Environmentally friendly concrete may be a step closer to reality after researchers from the University of Sydney successfully poured a layer of pavement made entirely of fly ash and waste material.

In its latest announcement, the University of Sydney says its researchers have successfully poured ‘green’ cement pavement made not from a unique mix of fly ash, and waste materials including ground glass and gaseous carbon dioxide.

Compared with a traditional pour using the same volume of concrete, the simple pour of the slab saved:

• 52kg of sand from being dredged
• 327kg of carbon dioxide being emitted into the atmosphere,
• (during production) the equivalent energy of 1,000 cups of coffee or driving a car over 1,800km.

Around the world, concrete is the most widely used man-made product due to its role as a structural material in buildings and infrastructure.

Advantages it delivers include durability; resistance to fire, weather and flood; good thermal performance; versatility and potential for reuse and recycling at the end of its life.

Environmentally, however, the material has a high carbon footprint due to the carbon intensive nature of the cement manufacturing.

As well, its production involves sand and aggregate dredging, which contributes to erosion and environmental degradation.

The concrete is made from a cement that uses fly ash and waste glass. Credit: Professor Ali Abbas

In a statement, Director of the Waste Transformation Research Hub and School of Chemical and Biomolecular Engineering researcher, Professor Ali Abbas , said the cement was designed to counteract the environmental impact of traditional concrete construction.

Traditional concrete production is energy and resource intensive, yet is one of the most common materials used by the construction industry,” said Professor Abbas, who worked alongside Delta Electricity, and in cooperation with recycling company, IQ Renew, construction materials and industrial minerals supplier Morgan Ash: an Adbri Company, to develop the technology.

“We sought to create a less energy intensive solution that would have less impact on the environment using carbon-capture and beneficially reusing materials that would otherwise end up in landfill.”

The concrete is made from a cement that uses fly ash – a by-product of coal combustion – and waste glass, which has traditionally been energy-intensive to recycle.

“Around 12 million tonnes of fly ash are produced each year in Australia. In our green concrete, we use fly ash as a cement replacement,” said Professor Abbas.

“Glass, on the other hand, has traditionally been an expensive and energy-intensive material to recycle. Less than half of the 1.4 million tonnes of glass produced each year in Australia is recycled. When crushed, glass can replace both sand and aggregates in green concrete.

“We are also testing an algorithmic intelligence technique that adapts the concrete blend to specific applications.”

Gaseous carbon dioxide is also directly sequestered or “locked” into the concrete in a stable mineral form, which prevents greenhouse gases from entering the atmosphere.

The researchers said greater environmental benefits could be realised when implemented on a larger scale. They plan to install another two eco-pavements on campus with differing blends to continue their trial studies.

Over the next 12 months the team will monitor the concrete’s performance, with the hope to later commercialise the technology and introduce it to the market as an alternative to traditional concrete.

Fly ash can be beneficially reused under the NSW resource recovery scheme.

(top image: After the first successful pour, the cement will be trialled across campus. Credit: Professor Ali Abbas)