'A Bridge NOT Too Far' - Copper Naphthenate Treated Softwoods for Bridge Ties

摘要

Long service life in bridge ties is a major goal for railroads since they are expensive and time-consuming to replace and critical to the overall logistics network. Increasing preservative retention to increase service life is not always feasible becauseof environmental concerns over preservative bleeding/dripping onto roadways, wetlands and waterways. Bridge ties and timbers have much larger dimensions than typical crossties. Hardwoods can take too long to air season, must be slowly kiln dried, and may be difficult to acquire at short notice. Softwoods such as southern pine and Douglas-fir are widespread, fast growing and can be easily kiln dried, meaning adequate stocks of large diameter ties are usually on hand. Copper naphthenate (CuN) has a longhistory in wood preservation and is finding increased usage as a treatment for wooden crossties and timbers. CuN has gained market acceptance in ties, not only because of its efficacy against decay fungi and wood-destroying insects, but also for its cleanliness and low environmental impact. CuN-treated ties were recently adopted by two Class 1 railroads to replace creosote-treated hardwood ties in several regions for both performance and environmental reasons. This paper reviews four recent bridge tie replacement projects using CuN-treated softwood ties, including both solid sawn and glulam. Full penetration into thick sapwood southern pine ties resulted in deep treatment without excessive bleeding or surface deposits.