Recycled materials in railroad substructure: an energy perspective

Abstract

Given that the current ballasted tracks in Australia may not be able to support faster and significantly heavier freight trains as planned for the future, the imminent need for innovative and sustainable ballasted tracks for transport infrastructure is crucial. Over the past two decades, a number of studies have been conducted by the researchers of Transport Research Centre (TRC) at the University of Technology Sydney (UTS) to investigate the ability of recycled rubber mats, as well as waste tyre cells and granulated rubber to improve the stability of track substructure including ballast and subballast layers. This paper reviews four applications of these novel methods, including using recycled rubber products such as CWRC mixtures (i.e., mixtures of coal wash (CW) and rubber crumbs (RC)) and SEAL mixtures (i.e., mixtures of steel furnace slag, CW and RC) to replace subballast/capping materials, tyre cells reinforcements for subballast/capping layer and under ballast mats; and investigates the energy dissipation capacity for each application based on small-scale cyclic triaxial tests and large-scale track model tests. It has been found that the inclusion of these rubber products increases the energy dissipation effect of the track, hence reducing the ballast degradation efficiently and increasing the track stability. Moreover, a rheological model is also proposed to investigate the effect of different rubber inclusions on their efficiency to reduce the transient motion of rail track under dynamic loading. The outcomes elucidated in this paper will lead to a better understanding of the performance of ballast tracks upgraded with resilient rubber products, while promoting environmentally sustainable and more affordable ballasted tracks for greater passenger comfort and increased safety.

Trends and Challenges in Railway Sustainability: The State of the Art regarding Measures, Strategies, and Assessment Tools

“…Regarding the sub-ballast layer, the literature shows that sustainable solutions are related to the use of the following: non-conventional bituminous mixtures made with recycled materials [6], which are able to ensure great layer stability; and geocell-reinforced coal mine overburden waste materials [46], which have been proved to ensure a decrease in vertical settlements, lateral deformations, and subgrade stresses. A recent study [47] demonstrated that the use of recycled rubber products, such as CWRC mixtures (i.e., mixtures of coal wash (CW) and rubber crumbs (RC)) and SEAL mixtures (i.e., mixtures of steel furnace slag, CW and RC), to replace sub-ballast, tire cell reinforcements for sub-ballast and under-ballast mats increases the energy dissipation effect of the track, hence reducing the ballast degradation efficiently and increasing the track stability.…”

Experimental Analysis of Hot-Mix Asphalt (HMA) Mixtures with Reclaimed Asphalt Pavement (RAP) in Railway Sub-Ballast

“…Global experiences demonstrated that the construction of sub-ballast [ 20 , 21 ] is a strategic solution for high-speed and high-capacity lines [ 11 , 22 , 23 ], although it has higher environmental and economic costs [ 24 , 25 ]. In the last few years, extensive efforts to address environmental protection led to the adoption of low-impact mixing and laying technologies and to the use of secondary and/or high-performance raw materials, low-temperature asphalt mixtures, modified bitumen, and high-performance additives [ 26 , 27 , 28 , 29 , 30 ]. In particular, mixtures modified with rubber and polymer returned interesting results in terms of fatigue resistance [ 31 , 32 ], mechanical properties [ 33 , 34 ], and damping vibrations [ 35 ].…”

The Effect of Waste Ballast Aggregates on Mechanical and Durability Properties of Standard Concrete

“…One of the construction/demolition wastes used in these applications is waste ballast (WB). A large amount of WB is formed due to the increasing need for new infrastructure along with developing rail track technology [ 40 ]. For example, Indian railways supplied around eight million cubic meters of ballast in 2017–2018 [ 41 , 42 ].…”