Interaction of CCA Preservative Treatment and Redrying: Effect on the Mechanical Properties of Southern Pine

Preservative treatment with chromated copper arsenate (CCA) and kiln redrying can adversely affect the mechanical properties of southern pine. To assess the extent of the effect we treated small clear specimens to CCA target retentions of 0.25, 0.40, 0.60, 1.0, or 2.5 pounds per cubic foot (pcf) and dried at maximum drybulb temperatures of 80?, 140?, 180?, or 220?F. A highly significant interaction existed between the level of CCA treatment and redrying temperature. When southern pine treated to CCA retentions of up to l.00 pcf was dried at temperatures of <140?F and compared to similarly dried controls, neither maximum crushing strength (MCS), modulus of elasticity (MOE), modulus of rupture (MOR), nor work to maximum load (WML) were affected; when dried at >180?F, MCS and MOE were not affected, MOR was reduced 11 percent and WML was reduced 37 percent. When pine treated to a CCA retention of 2.5 pcf was dried at temperatures of <140?F, MCS was increased by 15 percent, MOE and MOR were not affected, and WML was reduced 27 percent; at 180?F, MCS was increased 9 percent, MOE was not affected, MOR was reduced 12 percent, and WML was reduced 46 percent. At 220?F, MOE was still not affected while MCS was reduced 9 percent, MOR was reduced 30 percent, and WML was reduced 68 percent. Statistical models were developed to quantify the response between CCA retention and the kiln-drying temperature. These models were used to establish guidelines for current Forest Products Laboratory studies on the response of CCA tested southern pine dimension lumber.

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