Effect of weathering exposure on the preservative and softening agent retentions, wood hardness and climbability of CCA-treated red pine utility poles
Besner, A.G.lbert, R.T.treault, P.L.brecque, J.
Forest products journal 49(10): 59-68
This study has been carried out to identify one or more wood preservatives capable of providing poles with climbability characteristics equivalent to those that the pentachlorophenol in oil (PCP-oil) treatment confers, in addition to eliminating some of the disadvantages. Wood poles taken from the same lot for each preservative formulation were installed at IREQ's outdoor test site at Varennes, Quebec. A number of untreated red pine poles and others impregnated with chromated copper arsenate (CCA) using various additives to counter wood hardening caused by CCA, such as an emulsion treatment (ET), a water repellent (ULTRA), and polyethylene glycol (PEG and PEGPLUS), were compared with PCP-oil-impregnated poles that constitute the reference treatment for Hydro-Quebec. The retention of PCP, oil, arsenic, chromium, copper, and additives was monitored in the first 0 to 0.5 cm of sapwood by periodically taking samples over an exposure period of 60 months. Changes in the surface wood hardness of the poles was monitored using a Pilodyn 6J. The moisture content in the first 1.5 cm from the pole surface was also measured using the ASTM D 4442-84 weight-loss method. The chemical analysis shows that there is no treatment that fully prevents leaching of the CCA components. There is some indication that the arsenic, chromium, and copper losses vary according to the type and persistency of the additives used in the CCA formulation, which can act either as a water carrier or as a water-repellent film. Significant losses were noted for additives used with the CCA formulation. These losses could reach roughly 75 to 85 percent in the first 0 to 0.5 cm of sapwood over 60 months of exposure. Although the losses noted for the oil of the PCP-oil treatment are similar to those of the CCA additives, they have very little impact on changes over time in wood hardness, which is not the case for the ET, PEG, and PEGPLUS additives. The disappearance of these additives in the first 0 to 0.5 cm below the surface allowed the wood to achieve an equilibrium moisture content at levels as low as 9 to 10 percent, which had a direct effect on the hardness from the perspective of the Pilodyn or the linemen's gaff. An estimate of the linemen's appreciation of these poles allowed the authors to conclude that although they met Hydro-Quebec's criteria at the time they were installed none of them was able to maintain over time the percentage of acceptability required to meet the performance achieved by the PCP-oil-treated red pine poles.