Effects of long-term elevated temperature on CCA-treated southern pine lumber

The objective of this study was to determine the influence of extended high temperatures on the mechanical properties and chemical composition of southern pine treated with chromated copper arsenate (CCA). Different treatment processing factors were evaluated to determine their effect on the rate of thermal degradation for CCA-treated lumber. When compared to untreated lumber, CCA-treated lumber (9.6 kg/m3 (0.6 pcf)) exhibited accelerated thermal degradation on extended exposure to temperatures near 65?C (150?F) and 75 percent relative humidity. Both modulus of rupture and work to maximum load were significantly reduced, but modulus of elasticity was not affected. The effect of CCA retention levels less than 9.6 kg/m3 (0.6 pcf) is unknown. Chemical analysis indicated that arabinose and galactose contents were reduced more than 50 and 25 percent, respectively, after the 160-day high-temperature exposure. The rate of change in arabinose and galactose content seemed directly related to the rate of strength loss. Results indicate a possible need to develop an independent temperature modification factor for design stresses of preservative-treated material intended for use in high- temperature environments.

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