Recycled plastic railway sleepers: a sustainable alternative to timber?

Railway sleepers made from recycled plastic have been installed at Richmond Station.

By Kim Ho, Assistant Editor, Infrastructure magazine

With China banning the importation of recyclable materials in 2017, the issue of what Australia should do with its waste has grown more and more urgent. A new initiative, backed by research funded by Sustainability Victoria, proposes one innovative solution: creating railway sleepers out of recycled plastics.

Look down at the tracks at Richmond Station in Melbourne – from behind the yellow line of course – and you won’t see concrete railway sleepers. Rather, those dark grey replacements are made of recycled plastic – a composite of polystyrene and end of primary life agricultural plastics from regional Victoria.

The sleepers are currently part of an 18-month trial by Metro Trains, during which they will be monitored against a variety of criteria. Should they pass the test, approval will likely be issued for deployment across Victoria’s Metropolitan Rail Network. Once approved, the sleepers will provide a suitable alternative for timber sleepers and low-profile concrete sleepers in mainline track.

Manufactured in Mildura in northwest Victoria by Integrated Recycling, the Duratrack® sleepers use local agricultural waste such as cotton bale wrap, vine covers and pipe from the mining industry, which was previously unable to be recycled and sent to landfill.

Recycled plastic makes up approximately 85 per cent of the content of each sleeper. This includes both rigid and flexible plastics alongside polystyrene, combined with virgin materials carrying specific functions to enable the performance required.

One kilometre of Duratrack sleepers (about 1,500 units) will use approximately 64 tonnes of recycled plastic. They are also fully recyclable at the end of their life – a major step towards creating a circular economy for Australian railway infrastructure.

Crucially, the properties the Duratrack® composite sleepers make them competitive with traditional sleepers on the market in performance, durability, and return on investment.

With a lifespan of up to fifty years, they last three times longer than timber sleepers and operate at par with concrete sleepers. They also require less maintenance than timber sleepers because they have low water absorption and are fire tolerant and resistant to termites, UV, fungal decay, rot and split.

These properties mean the sleepers’ environmental benefits are threefold: they reduce the need for timber resources; reduce concrete production (the second-largest carbon emitter in the world); and meaningfully recycle plastic waste.

Duratrack sleepers became the first Australian-made plastic railway sleep to meet Monash IRT's specifications for use.

Duratrack sleepers became the first Australian-made plastic railway sleep to meet Monash IRT’s specifications for use.

Developing the guidelines for rigorous testing

The big hurdle persisting throughout the development of the sleepers was the lack of standards for recycled plastic railway sleepers in Australia, which meant rail operators had no benchmark against which to assess the performance of this new material. Add to this the cost and time expenditure of testing, formulating and approving a new product – not to mention the inherent risks involved – and the undertaking was ambitious.

The Monash Institute of Railway Technology (Monash IRT) was brought on board to create the guidelines by which to measure the sleepers’ success.

The core component of the guidelines is to provide the required mechanical tests to critically evaluate whether the sleepers could functionally replace timber sleepers. A series of laboratory-based tests were proposed and designed to provide a comprehensive assessment of the sleeper and rail fastening system as a whole. These tests included:

  • An Electrical Test to assess the capability of the sleeper system to provide adequate electrical insulation for use in circuited tracks in both dry and wet conditions.
  • A Fastener Pull-out Test to ensure that the fastening system used to secure either the rail or baseplate to the sleeper had adequate strength to maintain an appropriate clamping force once installed.
  • A Bending Moment Capacity Test to ensure that there was sufficient strength in the manufactured sleeper so it would not break or deform excessively under load during service.
  • A Fastener Repeated Load Test to ensure that the fastening system in combination with the sleeper material was capable of resisting the repetitive vertical and lateral loads during service. This test was particularly important where sleepers were to be used in tight radius curves, as it provided confidence in the fastening system to limit lateral rail movement.
  • A Rail Seat Durability Test to measure whether the manufactured sleeper was capable of withstanding cyclic bending moments during service.
  • A Sleeper Lateral Stability Test was designed to compare the alternative sleepers against timber sleepers in terms of lateral resistance.

The testing confirmed that the plastic-composite sleepers’ load bearing capabilities and durability made them a safe, cost-effective and sustainable alternative to timber sleepers.

Ravi Ravitharan, Director of Monash IRT, said the sleepers are currently only made in trial quantities, but this will change once approvals are granted.

“With successful outcomes from the current feasibility trials, the costs of composite sleepers are expected to come down with dedicated production line to cater requirements of large quantities,” Mr Ravitharan said.

Vital support fosters growth

The development of the sleepers was made possible by an investment from Sustainability Victoria totalling $300,000 under its Research, Development and Demonstration (RD&D) grants program.

In line with the Victorian Government’s commitment to investing in research and development that will identify new end-market opportunities for recovered materials in local manufacturing, construction and other industries, one of Sustainability Victoria’s roles is to support the development of those end-markets for recycled products in Victoria.

The $4.5 million RD&D program supports projects that can increase the quantity of recycled products being sold in Victoria. Sustainability Victoria is currently funding numerous other projects that focus on recycling plastic into other types of infrastructure, such as footpaths, permeable pavements, municipal concrete structures, asphalt and roads.

Sustainability Victoria Interim CEO, Carl Muller, said the funding was about enabling Victoria’s growing circular economy.

“We need proven recycled content products and markets for those products to make recycling viable. This will build confidence and market demand,” Mr Muller said.

“With recent shifts in international markets, such as in China, there is an opportunity to develop strong local markets so the recovery of resources can be maximised.

“The environmental benefits of using recycled content products and materials are clear, including reducing the need for resources, reducing production of high energy products such as concrete and curbing greenhouse gas emissions from production.”

Recycled sleepers on a railway line.

Momentum is building for government and industry to explore the use of environmentally conscious infrastructure.

With technical and financial support, the Duratrack sleeper has achieved a series of green lights. In July 2017, it became the first Australian-made plastic railway sleeper to meet Monash IRT’s specifications for use. In April 2018 it also received provisional type approval from Queensland Rail (QR) and began a twelve month in-track trial on two freight lines in the Darling Downs and the Lockyer Valley.

Metro Trains provisionally approved the trial of Duratrack® sleepers in October 2018 and 200 sleepers were installed in Richmond mid-2019. V/Line also provisionally approved the sleepers for in-track trials at the new Wyndham Vale stabling yard. Their performance will be closely monitored by track inspection and compared with reference sleepers installed nearby.

The teams at Integrated Recycling, Sustainability Victoria and Monash IRT hope the tests will verify sleeper design and strength requirements, as well as additional benefits such as track compliance and noise abatement.

A vast criteria to meet

The outcome of these trials will dictate whether the plastics sleepers are suitable for their respective operating environments. Different environments place specific demands on the sleepers: different axle load and speed requires sufficient mechanical strength; different curve radii requires strong lateral holding capability for fasteners and so on. Different temperature cycles require sufficient lateral stability and gauge holding, to account for thermal expansion and contraction. Certain locations will require termite resistance.

But it was not enough for Duratrack® to meet these criteria alone. Other factors made the journey towards trials that much bumpier. There is a natural scepticism amongst rail engineers operating in a safety-conscious environment when asked to approve a new product. Whilst welcoming innovation, it is important to make sure the product will perform as expected.

Stephen Webster, General Manager of Integrated Recycling, said, “Sustainability needs innovation and collaboration to bring that innovation to commercial reality. The Duratrack® project required Monash IRT, Sustainability Victoria and the rail operators on this five-year journey.”

Each rail operator undertakes its own approval process, which was time-consuming before the in-track trials could commence. And since each state has a different rail gauge, one size sleeper does not fit all.

Despite the sleepers themselves crossing state boundaries, the plastic waste sourced comes exclusively from the Mildura region for the time being, as it makes economic sense to reduce transport costs and emissions associated with that process.

While there is work to do in the recovered resources and recycling space, momentum is building for government and industry to adopt more environmentally conscious infrastructure.

“Victoria is investing in a strong and sustainable circular economy that is environment, jobs and economy focused, where recovering resources and using recycled content products is the norm,” Sustainability Victoria’s Carl Muller said.

The recycled plastic railway sleeper trial represent a step forward in sustainable approaches to railway infrastructure construction and maintenance and sets a strong precedent for how we may use innovation to turn challenges into opportunities.

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