Flexural behavior of high-density polyethylene railroad crossties

Abstract

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.

Characterization and Model Validation for Large Format Chopped Fiber, Foamed, Composite Structures Made from Recycled Olefin Based Polymers

“…The MOE is calculated by measuring the linear portion of the load-deflection curve and dividing the flexural stress measured at any point in the linear region. It is worth noting that the crossties tested in this study meet and exceed the requirements for crossties based on AREMA requirements for both MOE and MOR as shown in [4]. Even though the load-deflection curve is non-linear as shown in Figure 9, the first study in the region of interest for the crosstie is taken to be the initial linear region.…”

“…In the past decade, large format recycled polymer composites have found applications in composite structures such as short bridges, construction mats, railroad crossties (sleepers), and so on. The use of recycled polymer composite crossties has increased, and thousands of composite crossties have been in service throughout the world [4]. A typical polymer matrix composite crosstie is shown in Figure 1.…”

“…Wooden crossties are being replaced with composite crossties made of recycled High-Density Polyethylene (HDPE) and Glass Filled Polypropylene (GFPP) because wooden ties have a shorter expected lifespan and require chemically toxic preservatives such as creosote to increase their lifespan. There is a desire for an alternative material because creosote is a known environmental hazard with various health issues, and it has the potential to contaminate the water and soil when used in crossties [4]. Researchers have extensively reviewed alternative materials for crossties and noted fiber polymer matrix composites as a reasonable alternative solution (see, e.g., [5][6][7]).…”

“…In a subsequent paper, Bajracharya et al [29] extended the study by using glass fibers to the plastic solid wastes and used the modified rule of mixtures and FMA to predict the strength and elastic properties of glass fiber reinforced plastic solid composites by using constants to account for orientation and fiber length factor. Lofty et al [4] studied the performance and flexural behavior of composite crossties made of HDPE using an FEM with model inputs based on tensile tests from dog-bone specimen obtained from the manufactured crosstie.…”

Strength Prediction Sensitivity of Foamed Recycled Polymer Composite Structures due to the Localized Variability of the Cell Density Distribution

“…With the intent of reducing waste and also reducing the use of high density wooden structures, themselves a depleting resource, recycled polymer composite structures are being used as crossties (sleepers), marine pilings, short bridges, and other load bearing applications. Researchers have demonstrated the feasibility of these structures as viable load bearing applications, which are being used all over the world [5][6][7].…”