Crossties is published for users and producers of treated wood crossties.
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TACT US A DVERTISE RTA EVENT CALENDAR S tella-Jones C orp. Wheeler Lumber R ailway Tie A ssociation Nisus Corporation Corporation Nisus CROSSTIES • JANUARY/FEBRUARY 2015 1 7 M O R R E L L ples were immersed in water until the mois- ture contents in the largest samples had in- creased to 30 percent based upon weight gain of the largest specimens. This value was chosen because wood swelling ceases when the moisture content reaches the fiber satura- tion point, which is generally around 30 per- cent. The number of checks and the width of the largest check were assessed on the widest face of each sample. The samples were then immersed again. This cycle was repeated three times. In addition, a subsample of the 1-by-4-by- 8-inch long samples of black gum were subjected to a repeated wet dry cycles and the ability of the wood surface to repel mois- ture was assessed between each cycle. The shape of a water droplet placed on the sur- face of a sample was observed over a 25- minute period as a measure of water repellency (Figure 2). Water droplets were rapidly absorbed by non-treated wood, reflecting the tendency for wood to absorb moisture. Samples treated with CuN in diesel followed a trend that was similar to the non-treated samples, indicating that this treatment imparted little or no water repellency to the wood (Figure 3). Creosote- treated black gum samples experienced only a minimal change in droplet shape over the 25-minute exposure period, indicating that the treatment imparted a high degree of water repellency (Figure 4). Water repellency by itself does not neces- sarily mean that the wood will perform bet- ter; however, wood that is slower to absorb moisture will be less likely to experience the continued wetting and drying that leads to checking and splitting over time. The longevity of this effect would also be important in terms of performance. For example, water repellency has little benefit if it is lost in a few wet/dry cycles; however, we saw no loss of water repellency over eight cycles with the creosote treated ma- terial. The results indicate that water repellency can be easily assessed using simple visual methods and that relatively few cycles are required to as- sess this property. However, repeated wet/dry cycles might be useful for determining if the water repellency is long lasting or only temporary. It is also important to note that the water repellency of preservatives such as copper naphthenate could be modified through alter- ations of the solvent either by using more aromatic components or by adding some level of another water repellent. Thus, this test might be useful for rapidly screening the potential effects of system modifications on per- formance. While water repel- lency can be an impor- tant attribute, the most important measure of performance is the abil- ity of a treatment to protect and stabilize the wood. The preservatives tested are capable of pro- tecting wood from bio- logical attack. However, the ability to stabilize the wood to limit the development of deep checks remains less thoroughly explored. Deep checks that develop in service can expose non-treated wood to potential fungal and insect attack, thereby reducing tie per- formance. Measuring the largest check proved to be a poor measure of stability because shrinking and swelling of the wood sometimes resulted in one large check ➤ 1 2 3 4 5 Example of water droplet characteristics over time for droplets applied to non-treated, creosote treated or copper naphthenate treated black gum samples. Figure 2 Examples of droplet shape as an indirect measure of water repellency where a contact angle >90 degrees represents highly water resistant and a contact angle of 0 represents no water repellency. Figure 3 Example of water droplets on the surface of a creosote- treated tie. The droplets would have an estimated contact angle of >90°. Figure 4 Contact angle > 90º Contact angle 90-60º Contact angle 60-30º Contact angle 30-0º Contact angle 0º MiTek ustries ustries MiTek