The Performance of Copper Naphthenate Treated Wooden Pole Stubs After 12 Years of Field Exposure¹ (cont)

Selected trees of loblolly pine (Pinus taeda L.) were cut, bucked into nominal 8-ft pole stubs and immediately debarked, and cut into matched 4-ft sections for use in this study.  Nominal pole stub diameter was eight inches.

After cooling overnight, each 4-ft pole stub was bored to the pith on third points around the circumference of the stub at the mid-point and 1-ft from the end of each stub.  Borings were segmented into the following zones for analysis: 0.0-0.5, 0.5-2.0, 2.0-3.0, and 3.0-4.0 inches from the surface.  Similar zonal segments from all stubs in a charge were combined for copper analysis by X-ray fluorescence spectroscopy (AWPA Standard A9).  The data were cross-checked by atomic absorption (AA) spectrometry (AWPA Standard A11) using wet ashing procedures (AWPA Standard A7).  In December 1987, half of the treated pole stubs were placed 18 inches into the ground while the remainder were placed horizontally on treated 4x4s in above-ground exposure (Figure 2).  In 1999, selected pole stubs were bored and reassayed using AA spectroscopy.

Poles representing the extremes in the treated population were chosen.  For pole stubs placed in ground contact, four borings were taken at quarter-points mid-way between the ground line and the stub top and four additional borings were taken mid-way between the ground line and the butt end of the stub.  For stubs exposed above ground, four borings were taken at approximately mid-length.  One boring from each position was reserved for future testing while the three from each location were separated into the 0-0.5, 0.5-2.0, and 2.0-3.0 inch zones for assay.  The three cores for each zone and location were combined for assay.  All pole stubs, whether assayed or not, were physically examined for signs of decay by visual inspection, sounding, and probing.

 RESULTS AND DISCUSSION

The combinations chosen for evaluation are given in Table 2.  The steam conditioning represents the most severe initial conditioning step, while the fixation cycle and steam flash cycles represent the extreme in post-treatment conditioning.

None of the cores taken exhibited any signs of biodeterioration, Sounding and probing of all the pole stubs (42 in ground contact plus 42 in above-ground exposure for a total of 84) failed to indicate any decay including colonization by soft rot fungi.  Heavy checking (Figure 3) in the above-ground portions of most of the pole stubs placed in ground contact was noted.  However, no colonization by wood-destroying fungi was evident.  The same was true for attack by insects.  No termite or beetle activity was noted.  The only insect activity was some fiber pull by wasps for nesting material.

Preservative gradients and copper losses for air-dried (AD) stubs in ground contact are shown in Figure 4 , Figure 5, and Figure 6 .  Gradients in the above-ground (AG) and below-ground (BG) portions of the exposed stubs are compared with the original gradients obtained immediately after treatment.  Copper losses in both zones are shown by bars.

Loss data for CuNap by treatment combination can be found in Table 3.  Both the initial gradients for AD stubs and those after exposure were relatively flat and linear.  Copper loss across the outer three inches in the AG portion of the air-dried stubs averaged 35% for stubs with no final conditioning, 30% for stubs which were steamed after treatment, and 7% for stubs undergoing a final fixation cycle.  In the BG portion of the stubs, the loss values were 38%, 34%, and –4% for no post-treatment conditioning, final steaming, and fixation, respectively.  The negative value represents a gain in preservative, most probably from movement by gravity from the top portion of the stub and/or radial movement from the interior of the pole stubs.  These data suggest that the incorporation of a fixation cycle at the end of the pressure period may enhance the resistance to leaching.

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