Sydney trials concrete made from industrial waste

The City of Sydney is trialling concrete made from industrial waste, replacing a 30 m section of road along an inner-city street in Alexandria. A busy road leading to Sydney Airport, Wyndham Street services high volumes of traffic and is thus considered a good candidate for trialling the integrity of the sustainable road material, which is made from a blend of concrete and industrial waste from coal-fired power stations and steel manufacturing.

Made from fly ash and blast furnace slag, the green construction material, known as geopolymer, generates 300 kg of CO₂ per tonne of cement compared with the 900 kg created by traditional cement production. The low CO₂ concrete has the potential to put the 400 million cubic tonnes of globally documented waste from the coal and steel industries to good use.

To assess durability, 15 m of traditional concrete has been laid alongside 15 m of geopolymer concrete, with nine sensors positioned under the concrete to monitor and compare how the material performs.

Researchers from UNSW Sydney will monitor the road performance for up to five years and, working with the CRC for Low Carbon Living (CRCLCL), will use the trial results to create industry guidelines for geopolymer concrete.

Professor Stephen Foster, Head of the UNSW School of Civil and Environmental Engineering and CRCLCL project lead, described 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,” Prof. Foster said.

“Concrete contributes 7% of all greenhouse gas emissions and in 2018 the world produced about 4.1 billion tonnes of cement, which contributed about 3.5 billion tonnes of CO₂. Alternative, low CO₂ concrete materials offer potential benefits in reducing the 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,” he said.

City of Sydney Lord Mayor Clover Moore said the city was committed to finding new ways to lower carbon emissions. “Projects like this geopolymer trial can result in new products that make a real difference in slashing carbon emissions,” Moore said.

“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,” she continued.

“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 25,000 m² per year.”

Industry partner Craig Heidrich, Executive Director of the Australasian (iron & steel) Slag Association and Ash Development Association of Australia, 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,” Heidrich said.

Image courtesy of City of Sydney.