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 compositi on of southern pine treated with chromated copper arsenate (CCA). Diff erent treatment processing factors were evaluated to determine their e ffect 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 temp eratures near 65-degrees-C (150-degrees-F) and 75 percent relative hum idity. Both modulus of rupture and work to maximum load were significa ntly reduced, but modulus of elasticity was not affected. The effect o f CCA retention levels less than 9.6 kg/m3 (0.6 pcf) is unknown. Chemi cal analysis indicated that arabinose and galactose contents were redu ced more than 50 and 25 percent, respectively, after the 160-day high- temperature exposure. The rate of change in arabinose and galactose co ntent seemed directly related to the rate of strength loss. Results in dicate a possible need to develop an independent temperature modificat ion factor for design stresses of preservative-treated material intend ed for use in high-temperature environments.