11163 Synthesis of Published and Unpublished Corrosion Data From Long Term Tests of Fasteners Embedded in Wood: Calculation of Corrosion Rates and the Effect of Corrosion on Lateral Joint Strenght

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Product Number: 51300-11163-SG

ISBN: 11163 2011 CP

Author: Samuel L. Zelinka and Douglas R. Rammer

Publication Date: 2011

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In the past 5 years, several accelerated test methods have been developed to measure the corrosion of metals in contact with wood. It is desirable to contrast these accelerated results against those of long term exposure tests. While there have been several published long-term exposure tests performed on metals in treated wood, the data from these studies could not be used as a comparative baseline because the formulations and retentions of the preservatives were not reported or the amount corrosion was presented as percent mass loss instead of a true corrosion rate because the surface areas of the fasteners were unknown. This work reexamines four reports (two unpublished) that measured the corrosion of metals in treated wood. Where possible, the composition of the preservatives are reported from the original laboratory notebooks. In all cases, the percent mass loss data are presented in terms of a true corrosion rate by calculating the surface areas of the fasteners. The second part of this paper uses the long term corrosion rates to calculate the reduction in capacity of the joint using the yield theory equations from the National Design Specification for Wood Construction. Specific examples illustrate the loss of capacity with time using measured corrosion rates for wood treated with chromated copper arsenate and alkaline copper quaternary.

Key words: preservative treated wood, corrosion, yield theory, chromate copper arsenate (CCA), alkaline copper quaternary (ACQ)