Prestressed concrete sleepers (PCSs) are the most commonly used type of sleepers. They play an essential role in track performance, behaviour and safety. The focus of the published literature on PCSs has primarily been on quantification of dynamic load and resulting structural behaviour of sleepers, interaction with other components of track and failure mechanisms. While structural performance of PCSs is very important and researched as reflected by the large volume of published literature, concrete sleepers also need to meet the durability requirements. It is known that only a small percentage of concrete sleepers remain in service when reaching their intended design life, resulting in heavy maintenance and replacement costs. This paper reports a summary of the review of literature conducted as part of a broader investigation undertaken at the University of Melbourne. The aim of the investigation is to establish the material requirements of the concrete sleepers in order to meet the structural and durability requirements. A summary of the latest works on dynamic responses (including natural frequencies and mode shapes, damping, bending moments and strain rates), failure modes, fatigue and durability aspects of PCSs are presented. Moreover, design approach and dynamic loads are discussed briefly. It is established that a comprehensive research with a focus on material characterisation for concrete sleepers is currently lacking.
Prestressed concrete sleepers (PCSs) play an essential role in structural response and performance of ballasted railway tracks. Due to defects in track or train components, high magnitude dynamic loads may generate at the rail head and transfer to the PCSs which can generate cracks in PCSs. Cracking from dynamic loads have been reported as the most critical problem of PCSs around the world and impose an early replacement of sleepers which is a financial burden to the rail industry. This paper investigates the effects of strain rates on the strength enhancement of PCS. By using available measurements, the strain rates are calculated at two critical points of the PCSs, the rail seat and midspan. Considering the dynamic increase factor (DIF) of concrete, the cracking loads of a PCS are calculated and are compared with commonly occurring dynamic loads. Results show that the maximum strain rates at both rail seat and midspan are about 0.08 and 0.016 1/s, respectively. The increase of cracking wheel load due to the strain rate effects is about 5 to 26 percent. The results are also shown to be able to demonstrate the level cracking from dynamic loads with very short return periods.
Concrete wastes such as recycled concrete aggregates (RCA) make up a significant part of construction and demolition waste (C&DW) which can be used to minimize usage of natural aggregates and reduce carbon footprint. This paper studies the salt-scaling resistance of recycled aggregate concrete produced with pretreated RCAs. The test method for evaluating salt-scaling resistance in concrete according to DIN EN 1340: 2003 was performed. Four series of concrete mixes using natural aggregates, RCAs, manually pretreated RCA, and modified RCA in a desiccator were subjected to the different tests in terms of bulk electrical resistance in two directions (X and Y) before and after freeze-thaw cycles, ultrasonic pulse velocity, and weight loss of the surface layer of concrete specimens. Moreover, Scanning Electron Microscopy (SEM) of mixes was conducted and the microstructure of mixes considering the interface transition zone was studied. Results show that after exposure to cycles of freezing and thawing, the quality of concrete regarding ultrasonic pulse velocity did not change. The electrical resistance of specimens decreased significantly in X-direction and slightly in Y-direction after applying freeze-thaw cycles in all mixes. Nevertheless, surface modification of RCAs can increase electrical resistance and improve durability of concrete. SEM images show that the interface transition zone before and after freeze-thaw cycles remained unchanged which means strong bond between aggregate, new mortar, and old mortar. An estimation of the total charge passed indicated that all recycled aggregate concretes can be classified in a safe area and with very low chloride ion penetrability according to ASTM C1202.
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