The ability of boron and fluoride to migrate from a boron/fluoride rod was investigated over a 15 year period in Douglas-fir pole sections. Both components readily moved through the wood, but boron tended to be present at higher levels over the test reflecting the much higher boron content of the rods. The overall chemical levels suggested that higher dosages would be needed to more fully protect Douglas-fir poles.

No abstract

The ability of boron to diffuse from fused boron rods into surrounding wood was investigated on pentachlorophenol-treated Douglas-fir poles. Boron readily diffused into the wood surrounding the treatment holes and was present at protective levels in most poles within 1 year after application. The protected zone was generally confined to the treatment zone. Effective levels of boron were still present in this zone 15 years after treatment. Attempts to correlate the presence of decay fungi with residual boron levels indicated that these fungi were sometimes present in zones with boron at the lower threshold level of 0.5 kg m-3 boric acid equivalent (BAE), but most of the isolations could be explained by localized variations in distribution. Boron rods provided excellent long term protection against internal decay in Douglas-fir poles.

Wood guardrail posts are among the most common wood materials currently used in highway construction. Preservative treated hem-fir is an important species for guardrain applications in the western United States. The service life of treated timber post guardrail systems has been estimated to be between 10-20 years. However, there is surprisingly little information on performance of timber guard rails. One aspect of the service life estimate is wood durability. This study assessed the flexural properties, level of decay, and residual preservative levels in chromated copper arsenate preservative treated hem-fir guardrail posts removed from a project near Bellingham, WA. Increment cores were removed from each post for assessing preservative treatment and fungal colonization. The posts were then tested for flexure properties in a three point bending test. Posts that met the AWPA Standards for preservative penetration trended to have lower levels of internal decay after 20 years in service and nearly all posts tested retained sufficient flexural properties to meet AASHTO Standards.

Internal decay is a common problem in poles or timbers of thin sapwood species. Several internal treatments have been developed to arrest this attack, and these systems are widely used in North America. Although these treatments have been evaluated in numerous independent field trials, there is no single test of all treatments. The objective of this study was to assess the chemical distribution and fungal colonization in Douglas-fir poles treated with each of 13 different internal remedial treatments over a 10-year period. Metam sodium treatments provided the shortest protective period, with little evidence of residual chemical 3 years after treatment. Methylisothiocyanate (MITC) in pure form provided a very high initial flush of active ingredient and a longer protective period extending from 5 to 8 years after treatment. Dazomet, which must decompose to produce MITC, took slightly longer to reach effective levels, but was still present at effective levels 10 years after treatment. Chloropicrin, which has strong interactions with wood, was associated with the highest chemical levels after 10 years. Borates took longer to reach effective levels in the poles and their protective zone was narrower than the fumigants, but boron was still present at effective levels 10 years after application. The results illustrate the different properties provided by each treatment, but also show that all tested remedial treatments were effective within certain limitations.

No abstract

The effect of copper naphthenate treatment on electrical resistance of Douglas-fir utility poles was compared with similar poles either left untreated or treated with pentachlorophenol (penta). Penta-treated and untreated wood had similar electrical resistance shortly after treatment and after a 3-month outdoor weathering period. Electrical resistance of copper naphthenatetreated wood was more variable but consistently greater, indicating that poles treated with this chemical would not pose an increased risk to utility personnel working on them.

A solid, crystalline fumigant (dazomet) with and without a supplemental copper compound was evaluated as an internal decay control treatment on Douglas-fir poles in two long-term field tests. Methylisothiocyanate (MITC), the decomposition product of dazomet, was used as a measure of effectiveness. MITC levels in the wood were above the threshold near the groundline application zone within 1 year after treatment. MITC levels above the groundline were much lower, suggesting that the treatment zone would need to be extended to produce protection in these higher zones. The addition of copper sulfate markedly increased MITC levels. Copper naphthenate was slightly less effective as a dazomet accelerant, but slightly better than dazomet alone. The results indicate that dazomet treatment remains at protective levels for 10 to 12 years. This range is well within the typical inspection cycle used by most North American utilities.