Effects of Post-Treatment Drying Schedule on the Strength of CCA-Treated Southern Pine Dimension Lumber

The objective of this work was to determine the effect of post-treatment, high-temperature, and conventional drying upon the strength of CCA-treated southern pine dimension stock. A total of 318 pieces of No. 1 high-temperature dried dimension lumber (2 by 6) were randomly divided into three groups. Two groups were treated with CCA-Type A (average retention of 0.3 pcf). The third group was designated as the control group and not treated. The two treated groups were redried, one using a high-temperature schedule (HTD), the other a conventional schedule. After conditioning at 12 percent EMC conditions, the specimens were tested in edgewise bending as specified by ASTM D 198-74. The results indicated that the method of post-treatment drying did not affect modulus of elasticity or work to proportional limit. Modulus of rupture was significantly reduced by CCA treatment, but not by drying schedules. High-temperature redrying caused a reduction in hygroscopicity of that treated group, while the conventional redrying schedule did not. The reduced moisture content of the group redried using HTD apparently resulted in a significant increase in the mean fiber stress at proportional limit of that group. Significant strength reductions were associated with CCA-treated material whether conventionally or high-temperature dried. Drying southern pine dimension stock treated with CCA-A at temperatures of 190?F and above is not recommended, unless some strength loss can be tolerated.

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