Moisture Content Variation in Treated and Untreated Eucalypt Poles

Moisture content measurements were made over a period of 5 years on nine preservatively treated and untreated messmate (Eucalyptus obliqua) poles. The poles were installed at a test site near Melbourne, Australia in 1966. Three of the poles were pressure treated with creosote, three pressure treated with CCA waterborne salts and three were left untreated. Preservative penetration was limited to the sapwood in all the treated poles. Measurements of moisture content were made on plugs taken soon after felling and immediately before and after preservative treatment. Further measurements were made at 10, 30, 90, 180, 365, 730, 1095, and 1825 days after treatment. At the time of each sampling two plugs were taken from the opposite sides of each pole at positions about 4 feet above groundline. The length of plug was approximately 5 inches. After sectioning into five zones the moisture contents of the 90 specimens generated at each sampling were calculated. Creosote treatment retards the drying of the heartwood to an extent that in eucalypt poles of 12 – 15 inches diameter the centers remain well above fiber saturation point even after 5 years. The heartwood in salt-treated poles dries in much the same way as it does in untreated poles with the central heartwood moisture content falling to around fiber saturation point after 3 to 5 years.

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