Effective and eco-friendly solutions for Australia's railways

The surge in rail demand in Australia can be attributed to several key factors, including ongoing urban and regional population growth, expanding trade activities and the recognition of the environmental advantages of rail over road transport.

To meet this growing demand and ensure efficient operation of railways, it is crucial to prioritise timely upgrades to the materials and techniques used in railway construction. These upgrades should not only accommodate rising demand but also reduce the frequency of maintenance cycles.

A primary focus of these upgrades should be the incorporation of sustainable materials and environmental practices.

The weight of railway demand

The layer of crushed stones beneath train tracks, known as the ballast layer, ranges from 200 to 300 mm and is designed to withstand the maximum impact caused by train loads. However, these stones can break over time as a result of impact, creating a frequent need to replenish ballast with freshly quarried materials. Rail authorities have identified this as one of the most expensive items in their track maintenance schemes.

Recycled rubber to the rescue

To optimise track maintenance costs and while enhancing passenger comfort and safety, the construction of rail tracks requires the use of appropriate materials and improved techniques for ballast and its layer formation. Extensive research conducted by the Transport Research Centre at the University of Technology Sydney (TRC-UTS) has demonstrated that incorporating recycled rubber conveyor belts, waste tyre segments, or their derivatives in track substructures can enhance track performance and prolong its lifespan.

Implementing these research and development outcomes from theory to practice was conceptualised through a close collaboration between the Australian Research Council Industrial Transformation Training Centre for Railway Infrastructure (ITTC-Rail) and Sydney Trains, with Bridgestone and EcoFlex as industry partners. This collaboration, which commenced in 2018, led a world first implementation of three innovative approaches to track sections at the Chullora Technology Precinct. These approaches were tested according to the specifications outlined by the Transport for New South Wales (TfNSW).

This field trial allowed the performance and feasibility of these innovations to be evaluated on a larger scale and delivered valuable insights into the adoption across future railway infrastructure projects.

Below I highlight the three-fold solution used in this collaboration that will revolutionise our railways.

Energy Absorbing Rubber Seam

Recycled conveyor belts are transformed into 11mm thick rubber seam grids using the waterjet cutting method. These grids are strategically positioned beneath the ballast layer to interlock the stones and also act as shock-absorbing dampers. By effectively resisting lateral movement and maintaining the stability of the track formation, the rubber seams ensure long lasting track integrity.

Additionally, the rubber material acts as a cushion, absorbing and dissipating impact energy from rail corrugations, track imperfections, and wheel wear.

Rubber intermixed ballast

Large-scale laboratory tests demonstrated that rubber granules derived from waste tyres can replace a portion of the high-quality and increasingly scarce crushed stones used in the load bearing ballast layer.

The composition of rubber granules is carefully determined to minimise particle breakage during train operations, surpassing the performance of conventional tracks. The inclusion of rubber particles reduces friction and wear between rock particles, so reducing the maintenance per year by around 40%, thus extending the average life span of ballast.

The track construction process is similar to conventional methods, utilising readily available volumetric mixers to blend natural rock aggregates and rubber granules to the desired proportion.

This approach offers technical effectiveness, extended ballast lifespan, and compatibility with existing construction equipment, making it a promising avenue for sustainable and efficient railway track construction and maintenance.

Infilled tyre cell foundation

The infilled tyre cell approach involves repurposing used car tyres by removing one side rim and filling the tyres with granular waste materials like used ballast or coal wash.

The filled tyres are then arranged in a grid pattern beneath the ballast layer. The innovative structure serves two purposes: reducing lateral movement of the track formation and minimising the load transfer into the untreated ground beneath the track.

By dispersing the load and ensuring an even distribution of forces, this approach reduces the risk of track settlement and associated maintenance issues.

Circular economy on track

Fundamental and applied research efforts like the Chullora field tests have shown that the blending and placement of these new materials in the track substructure can be technologically superior to the current minimum technical standards prescribed for conventional tracks.

The combined implementation of rubber seam grids, rubber intermixed ballast, and infilled tyre cell foundations offers a comprehensive solution to improve railway tracks. It enhances track stability, extends the lifespan of the ballast layer, reduces maintenance requirements and promotes sustainable and efficient railway infrastructure.

These innovations are an attractive way to reduce Australia’s carbon footprint while embracing the circular economic perspectives strongly encouraged by the state and commonwealth governments in Australia.