Developing a Standard to Assess Water Repellency and Dimensional Stability of Preservative Treated Railroad Ties and other Large Timbers

摘要

Moisture content variations in wood can have substantial effects on dimensional stability leading to the development of deep surface checks that further enhance moisture uptake and ultimately encourage deterioration. The horizontal exposure of wood crossties makes water repellency and dimensional stability particularly important in railroad applications. Ties are typically preservative treated to prolong service life. Preservatives primarily protect against insect and fungal attack, but many also alter hygroscopicity and enhance dimensional stability. Currently, there is no standard method for assessing water repellency and its interaction with dimensional stability in large wooden members such as railroad ties. Potential methods for assessing moisture behavior were investigated on red oak {Quercus rubra) without treatment or materials treated with creosote, pentachlorophenol, or ammomacal copper zinc arsenate. Dimensional stability and water repellency were evaluated after each of eight accelerated wetting and drying cycles using digital image analysis techniques to quantify checking and observing water droplet contact angle over time, respectively. Water repellency varied widely with cycles, but creosote and pentachlorophenol treated samples provided the best resistance to moisture uptake. Dimensional stability was more variable and more dependent on treatment in terms of check development. The results of this work will be used to develop a rapid, reproducible, and cost effective method for assessing the water repellency and dimensional stability of preservative treated wood used in railroad and other applications.