Laboratory Immersion Method for Accelerated Prediction of Preservative Leaching from Pressure-Treated Wood Exposed to Precipitation
Keywords:Wood preservative, leaching, precipitation, accelerated test methods, immersion
This paper reports on the development of accelerated laboratory methods to allow estimation of preservative leaching from pressure-treated wood exposed to precipitation. End-matched lumber specimens were pressure-treated with a boron-copper formulation and exposed to either natural weathering for one year, laboratory immersion protocols, or a laboratory simulated rainfall protocol. The rainfall run-off or immersion water was collected at intervals according to the method used and analyzed for concentrations of copper and boron. Of the laboratory methods evaluated, the simulated rainfall approach resulted in leaching patterns most similar to outdoor exposure, especially in the case of copper. However, this method is relatively complex and not ideally suited for standardized use. Although the immersion methods evaluated initially exaggerated leaching, reasonable approximations of leaching from one year of natural weathering were achieved with accelerated testing. Models were developed to relate hours of immersion to millimeters of precipitation, and used to evaluate how well the immersion methods might predict leaching from natural weathering over many years of exposure. One of the methods produced boron and copper leaching estimates that were within 15% and 7% (respectively) of losses predicted for wood exposed to 5 years of natural weathering. The results indicate that laboratory immersion methods have value in estimating long term preservative leaching from treated wood products exposed to precipitation.
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