Hardwood timber has been the predominant material of choice for crossties since the establishment of the railroad industry in the US. Recently, several concerns, including higher speeds, heavier loads, durability and negative environmental effects associated with deforestation and wood-treating chemicals, have invoked the railroad industry's interest in alternative materials for crossties. Currently, several manufacturers offer alternative and sustainable solutions using different recycled plastic composite materials. Thousands of plastic crossties are currently in service in a wide variety of railroad applications. Several researchers have been studying and testing these new materials, specifically high-density polyethylene, however, their behavior when subjected to rail loading is not yet fully understood. Uncertainties in mechanical properties, failure modes and fracture render their performance and safety questionable. More research is required to properly characterize, describe and model the behavior of these materials as well as to assess the feasibility of implementing these materials in railway applications in terms of performance, safety, practicality and economy. Therefore, this study aimed to investigate the performance of plastic composite crossties through experimental testing and analytical modeling. A flexural testing program addressing two AREMA recommended tests for crossties; center and rail seat bending, was conducted. The behavior of the crosstie with the rail and fastening system installed was also investigated. An analytical finite element model, capable of simulating the flexural behavior of plastic crossties, was constructed using a material model that was calibrated using the experimental data. The plastic composite crossties demonstrated adequate performance throughout the experimental testing program. This paper also highlights the potential structural, social and economic benefits of implementing high-density polyethylene crossties in railroad applications.
Railroad spikes represent a vital component of the rail track system, as they fasten the rail to the supporting crossties. Thus, it is important to understand its behavior and effect on the fastening assembly to mitigate any local failure, which, in turn, could lead to system deterioration or damage. Currently, alternative solutions to the traditional hardwood timber crossties are increasing being adopted by the railroad industry in the USA, with recycled plastic composite crossties being among the available alternatives. Their sustainably, environmental benefits, durability and ease of installation render them an attractive and competitive solution. Several research programs have studied this material and its fastening system in the past; however, additional research is required to fully understand the behavior of these materials and their interactions with the fastening system components. This paper presents an investigation that aims to understand and assess the performance of typical railroad spikes used for recycled high-density-polyethylene crossties. The study encompassed a comprehensive experimental investigation and analytical finite element modeling. The testing program evaluated railroad spikes using static testing methods recommended by the American Railway Engineering and Maintenance-of-Way Association (AREMA) manual. These tests addressed the rail spike pullout and lateral restraint for both screw and cut spikes. Finite element models were constructed and calibrated using the data obtained from the experimental program in order to extrapolate on the experimental results and predict the behavior of full-scale systems beyond the scale of the laboratory. The results observed in this study showed great promise, surpassing all the AREMA recommendations, which highlights the potential of these materials if properly optimized and engineered. Screw spikes exhibited a very good performance, surpassing the minimum recommendations by a significant margin (up to more than 200%) and are thus are highly recommended for future implementation.
The effect of temperature on structural materials is a major concern in engineering applications. Thermoplastic composites are highly sensitive to temperature changes and recycled high-density polyethylene (HDPE) is no different in that respect. Temperature variations may alter the mechanical properties for even the best designed HDPE compositions. Thermoplastic materials usually experience a lower modulus of elasticity and higher ductility at elevated temperatures and a higher modulus of elasticity and lower ductility at low temperatures. Therefore, it is of vital importance to study and fully understand the nature and extent of this effect. This knowledge will enable the safe implementation of these materials in structural applications where low or elevated temperature exposure is expected. In this paper, an experimental testing program that aims to assess the effect of temperature variation on the performance of HDPE composite railroad crosstie is presented. It employs an AREMA-recommended flexural testing method for crossties; center bending, to investigate a practical operating temperature range; from 10 F (À12.22 C) to 125 F (51.67 C). The effect of the temperature variation has been studied for several vital performance criteria: initial modulus; modulus of elasticity; secant modulus; ultimate strain; and modulus of rupture. Finally, the development and calibration of temperature-scaling models capable of predicting these vital parameters at an arbitrary exposure temperature within the investigated range is also presented. The HDPE composite crossties exhibited favorable qualities and predictable performance variation due to temperature changes. Moreover, optimization strategies are recommended to limit and control the effect of temperature on the HDPE crossties.
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