A familiar sight on construction sites across the country are hi-vis vests. Playing an essential role in helping to increase visibility of personnel and improve safety on busy sites with machinery and equipment on the move, hi-vis vests are a mandatory requirement for high-risk work.
However, with many industries requiring staff to wear hi-vis vests in their work, this also generates a significant amount of clothing waste due to the short lifecycle of the reflective strips. With the reflectiveness fading after 25 washes, this makes the vests unsafe to use – meaning each vest is used for just six months on average before needing to be replaced.
Researchers at Victoria University found that end-of-life uniforms account for 11,000 tonnes of textile waste each year, of which 99 per cent ends up in landfill.
Melbourne social enterprise Assembled Threads is one company looking to address this waste. Set up in 2021, it provides training and employment in garment manufacturing for disadvantaged groups and recycles textiles including hi-vis vests into new workwear.
However, this diverts just a small amount of the total volume of discarded uniforms, so Assembled Threads reached out to Victoria University to see if synthetic textile waste could be reused within concrete – diverting a higher portion of waste back into reuse but also driving research into a more resilient concrete product.
Concrete additive
Research into concrete additives has included reusing coffee grounds, coal ash and old tyres. A research team at Victoria University led by associate professor Malindu Sandanayake is furthering this with investigations into adding a combination of cardboard and textile waste made from hi-vis vests.
Speaking with Earthmovers & Excavators, Sandanayake says the overall aim was to generate a circular economy for locally-sourced textile waste, by diverting it from landfill and into concrete.
“When we started our research, we found out that around 6,000kg of textile waste is sent to landfill every 10 minutes in Australia,” he says.
“That by itself is a huge amount of waste that is being put into landfills. We then focused on how the construction industry contributes to this textile waste, particularly the high turnover of hi-vis vests.
“Assembled Threads has been working on recycling this hi-vis vest waste, but they mentioned to us that they were also generating a lot of waste material as a result. We therefore wanted to investigate how to reuse this textile material so that we can develop something sustainable.”
The research team was already looking into using cardboard within concrete as a way of improving its performance and reducing the amount of virgin cement used, so this was expanded to incorporate the synthetic textiles as well.
“As well as reducing the amount of virgin cement used, we were also looking to increase the fire resistance of the concrete,” Sandanayake says.
“We started with four or five different mixes, including just using the textile fibres by themselves and then the cardboard mixture by itself, alongside various composite mixes.
“We then developed around 12 different mix designs that we tested at laboratory stage. We also undertook durability testing and came up with a composition that was ideal for us to achieve a higher compressive strength compared to a normal concrete mix. At this point we took this to real-world trials to see how it performed.”
Proof in the pavement
The first pour of the textile and cardboard concrete was undertaken last year at a site on the Eastern Freeway upgrade in Melbourne.
To test the mixture in a low-stress situation, a pavement was poured alongside a reference mix. The pavements are still in place with ongoing observation of their wear.
“We have been looking at things like the crack pattern of the concrete mixed with textile fibres compared to the reference concrete when they are experiencing the same environment, humidity levels and weathering conditions, etc.,” Sandanayake says.
“What we’ve observed so far is that the mix including fibre material has a more pleasing appearance as it’s a bit lighter in colour compared to normal concrete, but also in terms of the crack propagation, there are fewer cracks.
“The other important thing is that this mix is showing superior fire-resistant properties. We hope that this inclusion of textile fibres will improve spalling, which is when concrete explodes at high temperatures. If that process can be delayed, in the case of a structural fire, this would give people more time to evacuate to safety.”
Sandanayake says that this improved fire resistance would also be a benefit in bushfire areas, where pavements and roads would be more able to withstand natural disasters.
To further investigate the properties of this new concrete mix, a second Melbourne trial will get underway in April this year, where a car park will be poured in Hoppers Crossing to test its performance under a higher traffic load.
“The site is around 100 square metres, and around 60 to 70 per cent of that would be the sustainable mix, with the rest being a reference mix so we can do a side-by-side comparison,” Sandanayake says.
“We are looking forward to seeing how it performs under the weight of vehicles.”
Commercial opportunities
With the textile mix showing positive benefits for structural integrity and fire resistance, Sandanayake says Victoria University has already developed a business case for real-world applications.
“The idea would be for us to start this as a low stress concrete application product, while we continue to do more research on developing this into a structural concrete material,” he says.
“We’re looking for companies to get involved in this and we are in discussion with a few concrete manufacturers. We are hoping that, in the next year or so, this product will be available for use on residential sector driveways for example.
“It’s been a great team effort between the research team here at Victoria University and our partners the Eastern Burke to Tram Alliance and Assembled Threads. We would like to invite any potential collaborators to join with us to do any testing work or do further research.”
For more information, associate professor Malindu Sandanayake can be contacted at Malindu.Sandanayake@vu.edu.au.
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