Resistance of Out-of-service Utility Poles as Related to the Distribution of Residual Creosote Content

Decay resistance of out-of-service poles was investigated to evaluate their effectiveness against biodegradation for possible recycling of these poles for composite products. Decay resistance was related to creosote content and creosote distribution in poles with service durations of 5 and 25 years and also freshly treated poles. Weathering of the poles had caused reduction in creosote content such that the residual content of the outer and upper portions of the poles was lower than the inner and bottom portions. Overall residual creosote content in the 5-year poles was lower than in freshly treated poles, but still higher than in 25-year poles. Above a 14 percent level ofresidual creosote content, the decay resistance ofweathered poles was still high. Below that level, the decay resistance decreased dramatically. Decay resistance of 5-year poles was mostly still comparable to freshly treated poles, while the decay resistance of 25-year poles, especially in the outer portions, was much lower and approaching that of untreated southern yellow pine. In reutilization ofout-of-service poles for composite woodproducts, components with lesser creosote content should be placed in the interior, while those with higher creosote content are more suitable for the outer part. T h e r e are about I SO million wood poles in service carrying electrical transmission and distribution lines. Each year, the ever-expanding basic electric and communication industries consume about 6 million treated poles. Approximately 75 percent of the annual consumption of the poles consist of southern yellow pine (SYP) (Pinus spp.) (13). Creosote was used in 17 percent of U.S. pole production (1 1 million ft.3) in 1993 and part of this volume was exported (4). About 1 to 2 million poles are being replaced each year, mostly due to mechanical wear and not because of biodegradation. As a result, utility companies are faced with a dilemma concerning the disposal of outof-service poles that still contain residual creosote. Popular waste disposal options, such as combustion and landfilling, are becoming more and more limited due to strict environmental regulations. Reutilization of waste poles by conversion to useful products, such as wood composites, can be regarded as one way to solve disposal problems. Moreover, the remaining creosote content in the poles can still have the preserving capability against decay. Nearly 5 million metric tons of preservative-treated wood are disposed of annually into landfills (11). About 2 million m3 per year of weathered utility poles treated with creosote are available for recycling (12). Standing poles in service are affected by long-term weathering, thereby causing changes in their creosote content and its distribution inside the poles. As a result, these changes may affect the effectiveness of the weathered poles, and also their converted wood products, against biodegradation. The authors are, respectively, Former Graduate Research Assistant, School of Forestry, Wildlife, and Fisheries, Louisiana State Univ. Agri. Center, Baton Rouge, LA; Principal Wood Scientist, Southern Res. Sta., USDA Forest Serv., Pineville, LA; Professor and Assistant Professor, School of Forestry, Wildlife, and Fisheries, LouisianaState Univ. Agri. Ccnter, Baton Rouge, LA. This paper (No. 99-22-0650) is published with the approval of the Director of the Louisiana Agri. Expt. Sta. This paper was received for publicatio~l in October 1999. Reprint No. 9037. %Forest Products Society Member. @Forest Products Society 2000. Forest Prod. J. 50(11/12):64-68.