According to the Railway Tie Association (RTA), “Wood crossties have been supporting North American railroads for more than 160 years. No other material even comes close to wood’s track record.” That is indeed true: Even with major technological advances in locomotives, railcars and track construction, creosote-treated wood crossties continue to account for over 90% of the current installed rail tie base in North America. Creosote-treated wood ties work exceedingly well, with the wood providing additional flexibility under load gradients and the creosote extending structural integrity by providing lubricity between the tie and the metal plate on which the rail track rests. In addition, creosote-treated ties can last for decades, resisting insect infestation, fungi and weather decay.
While wood remains (by far) the preferred material for North American railroad crossties, recently there has been a notable change in how these wood crossties are chemically treated prior to installation in railroad track beds. Traditionally, oak and other hardwood ties have been pressure-treated with approximately seven pounds of creosote per cubic foot (pcf) retained in each tie. This well-established method conforms to guidelines issued by the American Wood Protection Association (AWPA), a non-profit trade organization that develops and publishes industry standards for the preservation of numerous wood products, including railroad ties, home lumber, marine pilings, outdoor furniture, fence posts and utility poles.
Recently, however, the rail tie treating market has seen an increase in demand for “dual-treated” wood ties, which are first treated with borate compounds (an insecticide) and subsequently treated with creosote. Although the process of treating wood ties with both borate and creosote has been around for decades to enhance insecticidal protection against the Formosan termite, the dual-treatment process that has gained popularity recently deliberately reduces the amount of creosote retained in each tie. In fact, a “dual-treated” tie produced today generally contains 15-20% less creosote than the AWPA-recommended level of approximately seven pounds pcf depending on the species of wood being treated.
Several months ago, the AWPA voted on and ratified a standard for the “dual-treatment” rail tie treating process, providing specific guidelines regarding the pre-treatment of wood crossties with borate. The purpose of this new guideline was to help standardize the “dual-treatment” process across the wood treating industry. Under the “dual-treatment” guideline, the AWPA made no change to the long-standing recommended average minimum creosote retention level of approximately seven pounds pcf in a hardwood crosstie pre-treated with borate. In fact, the AWPA “dual-treatment” standard description specifically states that “The DOT [Disodium Octaborate Tetrahydrate, a.k.a. borate] treated tie shall be secondarily treated with creosote…at currently accepted retention levels.”
Despite the clear language of the guideline, railroads are requesting, purchasing and installing crossties that contain less than the minimum average creosote retention levels as specified by the AWPA. To be sure, the AWPA is not an enforcement agency and it has no authority to prohibit the manufacture or sale of any products that do not meet its guidelines. However, the AWPA has long been recognized as the industry standard bearer and its place in the wood treating industry is well-captured by its mission statement to seek to improve the performance and longevity of sustainable wood products by developing competent, reliable, international standards through an open, consensus-based process, and to serve society as a resource for knowledge on all aspects of wood protection.
AWPA Technical Committees, which consist of individuals from all facets of wood preservation, develop the AWPA Standards in an ANSI accredited process that ensures peer review and allows feedback from all interested parties, including manufacturers of preservatives and preservative components; producers of treated and untreated wood products; end users of treated wood; engineers, architects and building code officials; and government entities, academia and other groups with a general interested in wood preservation. The robust nature of the AWPA process has resulted in many industries adopting the AWPA standards into their own specifications and standards. But this has not been the case concerning railroad crossties pre-treated with borate.
The amount of creosote retained in a crosstie influences its lifespan
While biological deterioration, particularly in the high decay zones like the Southeastern U.S., is a major factor in determining the service life of a wooden crosstie, the mechanical integrity of the tie is equally as important. Crossties manufactured with alternative materials, such as concrete and plastic, have suffered performance issues due to mechanical failures associated with wear around the spike and tie plate areas. The presence of creosote not only functions to prevent decay, it provides lubricity between the tie and metal components of the rail system, thus reducing friction and mechanical wear of the tie. By reducing the amount of creosote retained in the tie, we contend such a tie will degrade sooner as friction on the tie increases. The decrease in mechanical integrity will translate into shorter service life and more frequent replacement – a costly and time-consuming process that we believe could be avoided by installing ties that meet AWPA specifications regarding average minimum creosote retention.
As a leading supplier of creosote and as an AWPA sponsor, we support the AWPA’s guidelines regarding creosote retention in railroad crossties. Developed over many years and backed by real-word evidence proving their efficacy, the AWPA guidelines are considered “best practices” in the numerous wood treating industries. In short, crossties that conform to AWPA creosote retention specifications are: 1) proven safe; 2) proven to last 30-plus years, on average; 3) proven to provide excellent resistance to insect and weather-related decay; and 4) proven to exhibit sound mechanical integrity over an extended time period. For these reasons, we recommend that railroad ties continue to maintain a “full charge” of creosote.comments powered by Disqus