The influence of sleeper material characteristics on railway track behaviour: concrete vs composite sleeper

Composite sleepers and bearers formed of polymers and sometimes steel or fibre reinforcement are an alternative to traditionally used timber or prestressed concrete counterparts. Composite materials offer the combined benefits of the compliant sleeper/ballast contact of timber with the longer service life of concrete. However, composite and timber sleepers have lower bending stiffness compared with concrete, and this affects their track performance. To better understand the influence of sleeper material on performance, a concrete and a composite sleeper were tested in the Southampton Railway Testing Facility. Test results were interpreted with the aid of finite difference and discrete element method numerical modelling. It was found that composite sleepers can provide a more compliant sleeper/ballast interface with increased numbers of ballast grain contacts of larger area that attenuate the peak contact forces. However, owing to their lower bending stiffness, they have more exaggerated deflection profiles and a tendency to become centre-bound compared with stiffer prestressed concrete counterparts.