Impact of Pretreatment Decay on the Mechanical Properties of Wood Railroad Ties

Abstract

Wood is the traditional material choice for railroad ties and one that is well-suited for the future. Wood railroad ties are preservative treated to ensure adequate service life. Borate treatment in combination with creosote or copper naphthenate (i.e., dual treatment) is a widely accepted practice. However, the timing of the borate treatment varies in different manufacturing processes and some ties are first treated only after the lengthy air-drying process. Before treatment, the wood is vulnerable to decay but there are limited data on the impact of pretreatment decay of wood railroad ties. This paper presents experimental testing to quantify the impact of pretreatment decay on the mechanical properties of wood railroad ties. Initial static bending and compression tests were performed on small clear samples subjected to different treatment schemes. Later testing included static bending, spike pull-out, and compression tests of full-size railroad ties. Several species were studied, including sweetgum and red oak, which are commonly used as railroad ties, and yellow poplar and southern yellow pine, which are not. Pretreatment decay resulted in as much as a 19% decrease in the average spike pull-out resistance and a 27% decrease in modulus of rupture in full-size ties. Degradation in mechanical properties from pretreatment decay was in some cases greater than the initial differences between species. The results of this study will enable more informed decisions to be made on the manufacture and use of wood materials in rail infrastructure and potentially enable the use of nontraditional abundant species.