Composites for Timber-Replacement Bearers in Railway Switches and Crossings

Recent developments in composite materials have resulted in their pilot adoption in railway industry, such as 'fibre-reinforced foamed urethane (FFU)', 'geopolymer concrete', 'recycled polymer', and 'CarbonLoc composite'. Railway track support systems are critical for safe and reliable operations of railway tracks. There are two types of support structures, which can be designed to be either a slab or a cluster of discrete bearers or sleepers. The choice of turnout support system depends on asset management strategy of the rail operators or maintainers. The aim of this paper is to present the criteria, fundamental and multi-disciplinary issues for the design and practical selection of composite materials in railway turnout systems. As a case study, a full-scale trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, is presented. Influences of the composite bearers on track geometry (recorded by track inspection vehicle 'AK Car' and based on survey data), track settlement, track dynamics, and acoustic characteristics are highlighted in this paper. Comparative studies of composite materials for railway track applications are reviewed and presented in order to improve material design process. This state-of-the-art review paper will also focus on practicality and environmental risks of composite components in railway built environments. It embraces the requirement considerations of new materials for use as safety-critical track elements.