Development of non-prestressed fibre-reinforced concrete sleepers

Railway sleepers are one of the essential parts of the ballasted railway tracks that provide support to the rails, retain the track gauge, and transfer the rail-seat loads uniformly to the underlying ballast layer. Prestressed concrete (PSC) sleepers are currently the most well-known railway sleepers used by the railway industry. It is estimated that there are around 400 billion prestressed concrete sleepers used in railway tracks worldwide and this number is increasing rapidly. The manufacturing process of the PSC sleeper requires relatively spacious indoor area with expensive machinery. Additionally, this manufacturing process needs heat curing and, therefore, is energy-consuming and pollutes the atmosphere due to the emission of greenhouse gases. This research proposes the application of non-prestressed concrete sleepers as an alternative to the currently used PSC railway sleepers. For manufacturing non-prestressed concrete sleepers, ultra-high tensile strength concrete is needed to resist the significant flexural tensile stresses generated within the sleeper under the design wheel load. In this research study, the reactive powder concrete (RPC) material, also called ultra-high performance fibre-reinforced concrete (UHP-FRC), is utilised for manufacturing the proposed non-prestressed concrete sleeper. In the first stage, the optimal UHP-FRC mix design is determined through experimental testing of trial concrete mixes and a mathematical optimisation algorithm. Then, the standard rail-seat positive moment and the cyclic/fatigue tests are carried out for the prototype UHP-FRC sleepers. The prototype sleeper satisfies the criterion to pass the standard rail-seat static test. However, the fatigue performance of the UHP-FRC sleeper needs further improvements. Indeed, the prototype UHP-FRC sleeper sample failed under fatigue (cyclic) loading after around 200,000 load cycles, while according to the Australian Standard, concrete sleepers are expected to resist at least 3 millions of load cycles.