In cities, concrete is everywhere: roads, parking lots, buildings, footways. But concrete comes at a big environmental cost, as production causes heavy emissions of carbon dioxide.
Alternate forms of the material, made from recycled industrial waste, have been on the radar for decades, but were never widely considered for commercial use. Until now.
In 2019, the city of Sydney embarked on the world’s first test to learn how geopolymer concrete performs as a greener alternative for paving roads. By monitoring the trial via sensors over the next five years, the city hopes to find not only a solution for its own sustainability efforts, but also a set of best practices that can be shared for widespread adoption.
Concrete’s environmental problems
The majority — about 70 percent — of this concrete is used in roads and footways. What if there was a more environmentally friendly solution? What if cities could use a greener material to pave surfaces and build construction?
Sydney’s Lord Mayor Clover Moore understands the role cities must play in the effort to find a better approach:
In theory, it’s a huge opportunity. But any materials used also have to be strong, safe, and easy enough to produce for widespread use. So Sydney set out to test its viability.
What is geopolymer concrete?
Sydney is experimenting with geopolymer concrete, a blend of fly ash and blast furnace slag — in other words, industrial waste from coal power stations and steel plants.
In addition to recycling byproducts, producing the geopolymer material creates only 300 kg of carbon dioxide per tonne of concrete. Standard concrete, on the other hand, produces 900 kg of carbon dioxide per tonne. This means that geopolymer offers an energy savings that’s about the same as the amount of electricity an average family home uses in two weeks.
It’s also tough stuff. According to one of the trial’s partners, Craig Heidrich, executive director, Australian (Iron and Steel) Association and Ash Development Association:
But is it as durable enough to be used commercially? The city of Sydney partnered with the University of New South Wales, the CRC for Low Carbon Living, and other organisations like Heidrich’s to find out.
Testing the geopolymer concrete
To test the concrete, the city selected Wyndham Street, a highly trafficked road in the suburb of Alexandria. The route leads to the airport, meaning the volume of cars should be a good stress test.
A 30-metre stretch of road (that already needed repair) was split into two sections: 15 metres were laid with standard concrete. The other 15 metres got the geopolymer concrete. A series of sensors was placed in the concrete to monitor its status and compare performance.
The test will be monitored for up to five years — though some early data should be available sooner, even after 12 months.
Ultimately, the city and researchers plan to turn the trial into a handbook that outlines best practices and details how to use sustainable concrete options in roads and construction.
It’s an effort that could have a huge global impact: By looking beyond local benefits and creating a shared resource for greener construction, Sydney’s geopolymer trial could help repurpose more than 400 million cubic tonnes of coal and steel waste worldwide, and help reduce carbon emissions. It’s a great example of how when local governments share their learnings, it can affect greater change beyond one community.
Sydney’s environmental mission
According to Sydney’s Lord Mayor Clover Moore, the geopolymer concrete trial is another step toward a more sustainable future: