World-first green concrete trial

City of Sydney green road trial

The City of Sydney is trialling the world’s first ‘green’ road on a major high-volume traffic road leading to Sydney Airport, with the concrete made from industrial by-products of coal-fired power stations and co-products from the steel industry. The project is an important step in creating road surfaces that are more environmentally friendly, while remaining commercial viable.

For most people, the suggestion of driving over industrial by-product would conjure up images of an apocalyptic environmental disaster. But, the City of Sydney is trialling a new ‘green’ approach that could be the first step in environmentally-friendly paving and footpaths.

The trail is being conducted on a 30m section of road on Wyndham Street – a busy inner-city Sydney street that leads to Sydney Airport in the suburb Alexandria. The site was chosen because the road was already in need of repair and as a major road leading to Sydney Airport, it has a high traffic volume, providing the perfect environment for an intensive trial.

Laid bare

As part of the trial and to test the green concrete durability, the City has laid 15m of traditional concrete and 15m of geopolymer concrete, a sustainable blend of concrete and recycled materials.

Researchers from the University of New South Wales and the CRC for Low Carbon Living (CRCLCL) have placed nine sensors under the concrete to monitor and compare how the geopolymer concrete performs against the traditional variety.

UNSW Sydney researchers will monitor the road performance for up to five years. This data will help create new industry guidelines for using sustainable concrete blends in pavements and roads, and will form the basis of a handbook titled Guide and Standard Specification for Construction with Geopolymer Concrete. This handbook will provide engineers and end users with practical information and specifications for using geopolymer in construction projects.

It is also hoped that the trial will reduce perceived risks about using geopolymers and demonstrate that alternatives to concrete can be found, paving the way for this approach to be used elsewhere.

City of Sydney green road trial

Green road part of a bigger picture

Sydney Lord Mayor, Clover Moore, said the City was committed to finding new ways to lower carbon emissions and have outlined measures as part of its sustainability strategy.

“I’m proud that the City of Sydney was Australia’s first carbon-neutral local government and that we’re continuing to take significant steps to reduce our carbon footprint,” Mayor Moore said.

“Projects like this geopolymer trial can result in new products that make a real difference in slashing carbon emissions.

“Local governments are responsible for maintaining local roads, so if we can purchase more environmentally sustainable materials, we can fight climate change and provide quality infrastructure for our community.”

Seventy per cent of concrete that is produced goes into pavements and footpaths, and concrete contributes seven per cent of all greenhouse gas emissions. In 2018, 4.1 billion tonnes of cement was produced around the world, which creates ten billion tonnes of concrete. This contributed about 3.5 billion tonnes of CO2.

However, geopolymer concrete has a 50 per cent reduction in carbon emissions compared with conventional cement.

“We’re continually working with concrete suppliers to reduce the amount of pollution and greenhouse gases emitted during the production of concrete for our local roads, and we already use sustainable green concrete for all our footway renewal works – which adds up to 25,000m² per year,” Mayor Moore said.

City of Sydney green road trial

Concrete construct

Made from fly ash and blast furnace slag, geopolymer generates just 300kg of CO2 per tonne of cement, compared to the 900kg from traditional cement production – saving the equivalent of the electricity used by an average household every two weeks.

Research has been undertaken since the 1990s into geopolymer, but it’s only now that it is being explored as a product that is not only better for the environment, but also commercially viable.

The low CO2 concrete has the potential to put the 400 million cubic tonnes of globally documented by-product from the coal and steel industries to good use. While a small amount is currently used in construction, much of it is currently stored on site.

Paving the way forward

Professor Stephen Foster, Head of School of Civil and Environmental Engineering, is the CRCLCL project lead and describes the trial as “a huge step forward”.

“This trial will help drive step change in the industry. Many concrete companies are already doing a lot to change, but this trial really gives it another push,” Professor Foster said.

“While we’ll monitor the road performance for up to five years, a lot of the data collected in the first three to 12 months of this world-first trial will be used to confirm our models and strengthen our predictions.

“Alternative, low CO2 concrete materials offer potential benefits in reducing greenhouse gas emissions associated with conventional concrete.

“This trial is important because we need demonstration projects to accurately assess the performance of geopolymer over time so that there can be broader uptake.”

Industry Partner, Craig Heidrich, the Executive Director of the Australian (Iron and Steel) Association and Ash Development Association, said the benefits of the trial will be far-reaching.

“Our collaboration with organisations such as the City of Sydney and the publication of the research findings will further demystify and promote the use of geopolymer concrete in construction.

“Geopolymer concrete has great engineering properties. It is a durable, high performance product that has a low carbon footprint when used in construction,” Mr Heidrich said.
“It’s a fundamental tenet in business that you need to be constantly innovating and investing into new technologies. This trial will provide real examples of geopolymer concrete use that we can all use.”

According to Dr Tommy Wiedmann, Associate Professor of Sustainability Research at UNSW, if all concrete was produced in one year was geopolymer instead of traditional concrete, this would save 12,000 kilotons CO2 per year.

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