Crossties is published for users and producers of treated wood crossties.
Issue link: http://crossties.epubxp.com/i/468004
roducts P agle Metal E Janes Co. Gross & Hurdle Machine Works K oppers Inc. R TA WEBSITE BECOME A MEMBER CONTACT CROSSTIES • JANUARY/FEBRUARY 2015 1 6 R E S E A R C H & D E V E L O P M E N T More than 90 percent of all ties used to support rails are wood and the majority of those ties are treated with creosote (Conners, 2008; RTA, 2014). Creosote has a number of attributes that make it attractive as a tie preservative. It is broadly effective against fungi, insects, and even some marine borers. Because creosote is an oil product, it has some ability to lubri- cate the tie and reduce mechanical wear. And, at the end of its useful life, creosote can be burned in a properly licensed facility to produce energy. One other important attribute of creosote is its tendency to make the wood more water repellent. Anyone who has tried to open a drawer when the humidity is high knows that wood will absorb water (either from rainfall or humidity in the atmosphere) and swell as its moisture content increases from 0 to about 30 percent. Repeated wetting and dry- ing causes wood to shrink and swell, and this process can result in mechanical damage such as splitting or checking (Simpson, 1991; USDA, 2010). Creosote slows the rate of moisture absorption, and this process is generally believed to improve the dimen- sional stability of a tie. The role of creosote in tie stabilization has been generally accepted but not necessarily stud- ied. Recently, however, a number of alternative preservatives have entered the tie market, including copper naph- thenate and ammoniacal copper zinc arsenate (ACZA). Both of these systems have long histories of successful use as wood preservatives in other applications, and there is little question about their ability to inhibit fungal and insect attack. However, the ability of these treatments to repel water and potentially stabilize wood is less studied. Copper naphthenate is typically dispersed in a diesel solvent. This system could incor- porate a water repellent wax; however, this is not currently done. ACZA is a waterborne system with little or no inherent water repellency; however, water repellents could be added to this system as well. As these and other new systems are considered for use in ties, assessing ancillary attributes of each pre- servative will allow tie specifiers to make more informed deci- sions about chemicals. While there are tests to assess water repellency on small wood samples, these tests do not account for the subsequent effects on dimensional stability (AWPA, 2012; NWDMA, 1999). The development of a standard method for assessing the role of water repel- lency on stability of woods used for railroad ties would provide railroads with compara- tive data on the merits of new preservative systems. The purpose of this work was to develop a test method for assessing the ability of a pre- servative to resist water uptake and limit checking of wood used for wood ties. The goal was to determine the optimum species, test specimen dimensions and characteristics that would provide the best measures of stability. Air-seasoned white oak, red oak and black gum ties were cut into various sizes (Figure 1). The large samples represented a short section of a grade tie with no wane. The materials represented species that were easily treatable, moderately treatable and extremely resistant to treatment with slightly differing degrees of shrinkage when dried (Table 1). Samples were allocated to be non-treated or commercially treated with copper naph- thenate (CuN) in diesel or creosote to the current AWPA specification for ties. The samples were weighed after treatment. The radial and tangential dimensions of each sample were measured, then the sam- Source: USDA Wood Handbook, 2010 Examples of dimensions of samples tested for water repellency and stability following repeated wet/dry cycles. Table 1 Developing Test Methods For Assessing Performance Attributes Of Railroad Ties BY H. GREELEY BECK, JEFFREY J. MORRELL & DAVID A. WEBB Figure 1 MiTe Industr Industr MiTe