Paving the way

Research by Melbourne’s Swinburne University of Technology has found a potential new use for flexible plastics and glass fines in the construction of footpaths.

An estimated 257,000 tonnes of glass is generated each year in Victoria, with 52 per cent made up of glass fines and stockpiles and about 76 per cent of the total generation recovered.

Likewise, flexible plastics contained three per cent by weight of landfilled waste in 2009. That’s according to fact sheets collated by statutory authority – Sustainability Victoria.

For flexible plastics, the market risks are contamination, high costs and a lack of technology processing options.

Recycled glass has been sensitive to price changes and stockpiled, while medium to long term contracts of glass cullet feedstock favoured by industry may cause some operators to hedge their bets against price volatility.

Fortunately, product research and development is helping develop new markets for glass fines, particularly in civil construction and flexible plastics, which are being made into bollards, fence posts, speed humps and outdoor furniture. In the area of flexible plastics, a 2013 report, Assessment of recycling infrastructure: current status and future opportunities, by the Australian Packaging Covenant Organisation suggests Victoria requires more local processing capability in this area.

The progress for increasing markets for both materials is being supported by Sustainability Victoria’s Research and Development for recovered glass fines and flexible plastics grant program, which recently saw promising results through project research at Melbourne’s Swinburne University of Technology. It is one of seven projects taking place at other Melbourne universities, including RMIT and Monash University.

The research project was undertaken by Dr Yat Choy Wong and his colleagues Dr Alireza Mohammadinia and Professor Arul Arulrajah, who were awarded $100,000 by Sustainability Victoria and an additional $10,000 by industry partner Polytrade, to investigate new blends of concrete for footpaths incorporating flexible plastics and glass fines.

The goal of the research was to ensure the material did not compromise engineering standards required for its use, akin to using virgin materials, while reducing the carbon footprint linked to footpath construction.

The research proved in the lab that these materials could be incorporated into concrete footpaths, while still meeting the standard requirements and not compromising on mechanical properties. The next stage is to include local governments and the civil and construction industry in the process to increase the amount of recycled materials in footpath construction.

Dr Wong, Senior Lecturer at Swinburne University of Technology, says the research trialled a varying blend of plastic and glass with concrete, along with plastic and concrete on its own and glass and concrete by itself.

With a background in materials engineering, Dr Wong says he was inspired to reduce waste based on the issue of stockpiling recycled glass.

The ranges of material in footpath construction blend varied from a mixture of 10 to 50 per cent.

He says as you increase on strength using these materials, the megapascal (MPa) – a metric pressure unit used to quantify internal pressure and stress drops.

“Plastic is soft when compared to sand and cement as they are very hard materials, so it’s about finding the right balance,” Dr Wong explains.

“Certain councils will want a footpath strength of 20 MPa, but it’s not a universal consensus and it also depends on the additive of glass or plastic fines.”

As one example, he says a three-metre by one-metre by 100-millimetre footpath could help divert more than 1000 PET bottles.

Material recycling provider Polytrade supplied Swinburne with the glass and flexible plastics fines, which were shredded via the company’s in-house crusher. From there, the researchers built a concrete cylinder sample of the concrete and blended the materials, of up to 100 by 200 millimetres in length. The footpath sat for 28 days to cure and was then placed into a universal tester machine under compression to crush the cylinder and discover any potential splits or cracks, putting the strength of the concrete to the test.

According to Dr Wong, the ASTM International standard, which provides a framework for commercially viable engineering, allowed the team to go anywhere near as high as 50 per cent materials.

Overall, Dr Wong is buoyed by the results and hopes the project can help divert more waste away from landfill.

“I think it’s a great way to deal with waste in a responsible way and we’re now trying to look at recycled bricks and see if we can produce a similar result.”

Pictured: Dr Alireza Mohammadinia, Professor Arul Arulrajah and Dr Yat Choy Wong with the compression test machine in the lab.