Effect of Drying Temperature on the Clear Wood Strength of Southern Pine Treated with CCA-Type A

The objective of this work was to determine the effect of post-treatment drying on selected properties of small, clear southern pine specimens cut from dimension lumber previously treated with CCA. Small, clear specimens were cut from 318 pieces of No. 1 high-temperature dried dimension stock (2 by 6) which was previously sorted into three groups. Two groups were treated with CCA-Type A (average retention of 0.3 pcf) and dried at 240?F.or 190?F. The third group was designated as the control group and was not treated. Two-foot sections were removed from each end of all pieces to provide blanks. Clear specimens were sawn from randomly selected blanks and conditioned at 12 percent equilibrium moisture content. Static bending, toughness, compression parallel to the grain, and hardness tests were conducted according to ASTM D143-78 (1). Dynamic vibration tests were also conducted. Treatment with CCA and the method of post-treatment drying did not affect bending, compressive, or dynamic moduli of elasticity, fiber stress at the proportional limit, hardness, maximum crushing strength, or damping capacity. CCA treatment followed by drying significantly reduced modulus of rupture, and there was no significant difference between the two drying methods. Work to proportional limit of material dried at 190?F was significantly reduced compared to the control group. Toughness was significantly reduced by treatment followed by redrying. High-temperature redrying caused a significant reduction in hygroscopicity while redrying at 190?F significantly increased hygroscopicity. These results agree with those of full-size bending tests. Significant strength reductions occur in clear pine when CCA-treated material is dried at temperatures of 190?F or greater. As a result, drying southern pine stock treated with CCA-A at temperatures of 190?F and above is not recommended.

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