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Where once concrete structures might have been expected to stand for 100 years or more, the typical lifetime is now 50 years or less as a result of regular updates and design changes, says Professor Vivian Tam, Associate Dean Research and Discipline Leader Construction Management at Western Sydney University’s School of Engineering, Design and Built Environment.
Often, once a concrete structure reaches the end of its life, the only option for most concrete waste is landfill. Only about five per cent is recycled into aggregate for low-grade pavement.
“My research looks into how waste concrete can go from being recycled into low-grade aggregate to instead being made as strong as virgin concrete,” Tam said.
Tam has developed a method to create such density and strength using recycled aggregate. It involves treating the aggregate in a pressurised chamber and injecting carbon dioxide. This increases strength and reduces water absorption, bringing the “CO2 Concrete”, as Tam calls it, up to the level of structural concrete.
At current Australian levels of production, CO2 Concrete could provide a net lifecycle benefit of $16 billion and save 2.68 billion kg of carbon dioxide emissions, she says, compared to a cost of $22 billion for using virgin concrete.
So what’s the problem?
“Engineers are reluctant to be the first to use the CO2 Concrete,” Tam said.
But things are slowly coming together, as smaller projects such as a drinking station for cows at Western Sydney University use the recycled product.
“I still don’t have an industry case study,” Tam said.
“Part of the problem is perceived risk, and part is the government not pushing projects to use it. In Japan, for example, the government says industry has to use more recycled materials on projects of certain sizes. That drives innovation.”