Synthesis of wood treatment alternatives for timber railroad structures.

Synthesis of wood treatment alternatives for timber railroad structures.

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  • Abstract:
    A wealth of information exists on various wood preservatives, treatment techniques, curing practices, and other engineered controls, along with alternative materials for replacement. This study was initiated to review and synthesize available information so that future bridge timber work could be completed in a manner that would optimize performance while eliminating damage to the environment. This project was triggered by dripping creosote from the Frankenstein Trestle within an environmentally sensitive area. Of the seven products evaluated, two are recommended for railroad bridge timbers: Copper Naphthenate and Creosote. Copper Naphthenate is commonly used in other jurisdictions, especially over sensitive aquatic environments and where preservative drippage is a concern. The product has low toxicity, is not listed as a restricted-use pesticide (RUP) by the U.S. EPA, and has shown equal or superior performance compared to creosote or pentachlorophenol. State DOTs including Iowa and Minnesota specify Copper Naphthenate for replacement and renovation of wooden bridges. Its only disadvantage is a limited supply of product currently. Creosote-treated wood has proven its effectiveness and longevity. To minimize potential issues, best management practices (BMPs) are required. These include specification of the correct retention rate for the wood species and type of use, specification of the empty-cell process, and the use of expansion baths for post-treatment. Only straight creosote or a 75/25 creosote/petroleum solution should be specified. As a result of this study, the Department’s specifications for railroad bridge timbers have been modified to reflect improved standards for preservatives, including treatment techniques and post-treatment procedures. In order to optimize performance while mitigating environmental concerns, a series of best management practices (BMPs) covering the design, purchase, delivery, handling, installation, and inspection of timbers are also being incorporated into future projects. It is expected that these recommendations will be incorporated into wooden highway structures as well.
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