Effect of variation in moisture content on the retention and penetration of CCA treated transmission poles

Abstract

Eucalyptus species commonly used as utility poles for transmission lines in Uganda are treated with preservatives which enhance their service life as they are known to be subject to decay and insect attacks while in field. Many treatment processes are available, however, pressure treatments with preservatives like Copper Chromium Arsenate (CCA) and creosote are regarded as the most effective. There have been frequent reports about premature failure of CCA treated poles while in service which is attributed to the preservative chemical, treatment method or wood species used. The objectives of the study were to determine the effect of moisture content on the penetration of CCA treated poles and its effect on the retention and to assess the retention and penetration of the preservative between different pole sizes. Poles in each category size (9m, 12m, 14m) with moisture content between 25% and 38% were subjected to the same treatment conditions of initial vacuum of 84Pa for 15 minutes to remove the air from the wood cells and create room for the chemical, pressure of 850Pa for 40 minutes to pump the chemical deep into wood cells and a fin al vacuum of 50Pa for 15 minutes to stop bleeding and collect the kickback and there after stacked in the yard for 24 hours to obtain penetration and retention of the preservative. Full cell pressure treatment process was used to treat all the charges using CCA preservative. Both penetration and retention registered a decrease in uptake. The 12m poles registered the highest penetration with a mean penetration of 26mm while 14m registered the lowest with a mean penetration of 22.9mm. However, 9m poles registered the highest retention values with a mean retention of 22.8kg/m3 while 14m poles registered the lowest with a mean retention value of 22.1kg/m3. One-way ANOVA showed that moisture content in poles greatly affects preservative penetration and retention. For better treatment, it is recommended that Poles with low moisture content of 25% and below should be used as they give higher retention and penetration values that ensures adequate protection of poles hence their longevity in service. Research on how density of wood affects the penetration and retention levels of CCA preservative, the effect of treatment time on the penetration and retention of the preservative and research to assess how eucalyptus wood species including clones affect preservative penetration and retention should be carried out. Key words: CCA, Transmission poles, Eucalyptus species, full cell pressure process