Industrial waste concrete trial in the City of Sydney

The City of Sydney and the University of New South Wales are testing concrete made using industrial waste from coal-fired power stations and steel manufacturing.

According to UK non-governmental organisation Royal Institute of International Affairs, cement is the source of around eight per cent of the world’s carbon dioxide emissions every year.

The extensive carbon footprint has for decades prompted researchers to look for new and greener solutions to construction.

One alternative that has been looked at is geopolymer concrete. The material aims to significantly reduce CO2 emissions and is made using recycled industrial materials.

Geopolymer concrete has been researched since the 1990s, including in the research paper Geopolymeric concretes For Environmental Protection, published in Concrete International in 1990.

However, despite ongoing research efforts, practical results showing its durability and performance have only come into the spotlight during the last five years.

For the first time, the City of Sydney is trialling geopolymer concrete on a busy city road. It estimates the alternative only produces 300 kilograms of CO2 per tonne compared to 900 kilograms per tonne with traditional concrete.

The City of Sydney is trialling the geopolymer concrete on Wyndham Street in Alexandria, a road leading to the airport. The concrete is made using fly ash from coal-fired power plants and blast furnace slag, a bi-product of the steel manufacturing industry.

The road has been constructed with 15 metres of traditional concrete and 15 metres of the ‘green’ geopolymer concrete. The even spread ensures each section receives the exact same amount of traffic.

Lord Mayor of the City of Sydney Clover Moore says projects like this can result in new products that can make a real difference in reducing carbon emissions.

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

She says with 70 per cent of the concrete produced going into pavements and footpaths, there’s great potential to lower emissions from their operations.

The strip of concrete will be monitored over five years by the University of New South Wales (UNSW) and the Cooperative Research Centre for Low Carbon Living (CRCLCL).

Team will use results from the trial to create the first set of industry guidelines for geopolymer concrete.

Professor Stephen Foster, Project Lead and Head of School of Civil and Environmental Engineering at UNSW, says the trial is a huge step forward.

“This concrete compared to conventional concrete will halve the amount of CO2 produced in the process of making it,” Dr. Foster says.

Dr. Foster says despite being researched for nearly 30 years, the CRCLCL identified research gaps around the durability and performance of the concrete over the last five years.

He says now there is sufficient research to have confidence in the concrete’s performance.

The UNSW has performed a series of trials in a lab to determine the durability of geopolymer concrete to ensure it could perform to a high standard. For this trial, the university used commercial geopolymer concrete to demonstrate their findings.

The product is already commercialised by some small companies such as Wagners and Zeobond. For large uptake, Dr. Foster believes engineers need to have widespread confidence in its performance.

“This trial will help us to create a handbook to give engineers and owners confidence that if they use this material they won’t be ripping the road up in five to 10 years time,” Dr. Foster says.

He says the tests are incredibly important to demonstrate a product’s performance, particularly as it will be verified by an independent body, as opposed to a commercial operation. Standards Australia will develop the handbook for geopolymer concrete and its quality for industry use.

Dr. Foster’s current prediction for the test is there will be no difference between the performance of the geopolymer concrete and the traditional concrete.

“We expect the geopolymer concrete to perform at least as well as conventional concrete, if not better,” he says.

When monitoring the road the researchers will take two approaches: The first is visual, at the start of the trial photos were taken of the entire road surface. The team will then monitor those images for any visible changes.

The second is through sensors, nine were placed into the concrete slab to collect data on its movement.

“We are in the process now of getting the data loggers for the sensors up and we will be able to measure or see in real time how and if there are any changes to the performance of the slab remotely,” Dr. Foster says.

He says the team will monitor the road over a period of five years but after one year it will have a large amount of data and should be able to make reliable predictions of its durability.

“We will be looking to see the quality of its abrasion resistance, how well it will hold up under a traffic load and we will also monitor how well the concrete resists water and salt to determine if there is a faster or slower corrosion of the reinforcing steel inside the slab,” Dr. Foster says.

Once the durability and quality of the geopolymer concrete is proved, it is hoped the product will be scaled up for use industry wide.

The only difference in the making and construction of geopolymer concrete from traditional concrete is changing the mix design. Dr. Foster says there should be no discernible difference for on-site workers between geopolymer and traditional concrete.

“The main thing is, it uses the same equipment mostly as conventional concrete and there will be almost no requirement for retraining the workforce. As it is made and applied with the same equipment there is almost no cost involved,” he says.

While Dr. Foster acknowledges some government specifications may limit the use of geopolymer concrete, or any concrete with a certain amount of recycled material, he is hopeful this will change.

“I think one of the key things to avoid is being prescriptive in the way specifications are developed. At the moment there’s too much prescription by some government authorities. Specifications should focus on the performance a product needs to give and then let industry innovate around that,” Dr. Foster says.

He believes in the near future concrete will evolve to be more sustainable and all governments need to allow this.

“Whether it’s changing conventional concrete by using less cement and more bi-products or using waste products such as the fly ash, or using a replacement product such as geopolymer concrete to take all of the cement out, the whole industry is moving to try and reduce its carbon footprint.”

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