Effect of aging and temperature on the resistance to spur penetration in red pine poles treated with CCA-PEG 1000

The aim of this study was to measure the effect of aging and temperature on the resistance of wood fibers to the penetration of linemen’s spurs in utility wood poles. The measurements are made by simulating the principal movement of the spur in penetrating the pole on a mechanical test bench. The comparison involves specimens of wood distribution poles impregnated with a mixture of copper, chromium, and arsenic oxides containing polyethylene glycol with an average molecular weight of 1000. The results show that twice as much force is needed to drive the spur into the wood to a given depth when the outer-shell moisture content drops from 35 to 10 percent (800 N vs. 1600 N). Pole aging over a period of 4 years would result in a 62 percent increase in this force (1079 N vs. 1752 N) for specimens with a moisture content at in-service equilibrium. As for the temperature effect, the measurements at -35?C revealed a 23 percent increase in the force compared to those at the ambient (1079 N vs. 1327 N). Although these effects are not necessarily cumulative, they could affect the climbability of a pole. Meanwhile, measurements on a few specimens treated with pentachlorophenol in oil show only a slight sensitivity to in-service pole aging. Only the low-temperature environment (-35?C) increases the force required to drive the spur in the wood, by a value equivalent to the previous case. The chemical analyses allowed a relations to be established between the fiber resistance to penetration and the aging of the CCA-based specimens. The hardening of the wood could be attributed to the rapid leaching of polyethylene glycol in the area of spur penetration (loss of 71% in 24 mo. in the outer shell). Last, the mechanical test bench proved to be a far more sensitive instrument than the Pilodyn 6J for keeping track of variations in the pole surface hardness over time.

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