An investigation of the durability of UK grown softwood distribution poles CCA-treated by sap-displacement

  • Sandra Hainey

    Student thesis: Doctoral Thesis


    The decay susceptibility of UK grown Corsican pine, Scots pine, Norway spruce and Sitka spruce poles treated with CCA by the high pressure sap-displacement process, was investigated using full size poles in a field site and representative pole sections in an accelerated decay system.

    Analysis of cores removed from the field poles showed a significant difference in the treatability of the four wood species. While satisfactory uptake and penetration of copper, chromium and arsenic were recorded for Corsican and Scots pine and Norway spruce, significantly lower levels of CCA penetration and retention were found in Sitka spruce poles. The narrow preservative penetration and extensive checking recorded in Sitka spruce poles contributed to the isolation of decay fungi after only four years field exposure.

    Radial distribution of the three preservative elements showed a gradient of chromium and arsenic which generally decreased from pole surface to centre, however, in all species except Sitka spruce an intermediate peak in copper concentration was recorded. Analysis of core samples removed annually from the groundline region of field poles indicated that migration of the CCA salts had occurred. This migration appeared to be complete after the first year of field exposure. Significant increase in copper and chromium levels in soil adjacent to poles of each species, indicated that leaching of the CCA components had occurred from the poles to surrounding soil. This small leaching effect is not expected to have a significant adverse effect on protection of the poles or to act as a soil pollution hazard.

    Exposure of pole sections to the natural soil microflora in the accelerated decay system resulted in untreated control sections suffering extensive soft rot decay of their curved and checked surfaces. Soft rot attack of CCA-treated sections was however, limited to small surface pockets at the untreated or poorly treated regions of their checked surfaces.

    Inoculation of the pole sections with basidiomycete fungi produced major differences in the type and location of decay development between the untreated and CCA-treated samples. Despite the presence of a heavy basidiomycete inoculum, decay of untreated control sections continued to be due to soft rot attack of curved and internal checked surfaces. Severity of decay was in the order of Corsican pine > Scots pine > Norway spruce > Sitka spruce. Decay of CCA-treated sections however, was produced principally by internal basidiomycete attack with large internal pockets of brown rot decay in the Sitka spruce sections. Severity of decay was the reverse of that for untreated pole sections i.e. Sitka spruce > Norway spruce > Scots pine > Corsican pine. The unexpected patterns of decay in CCA-treated pole sections was linked to the presence of CCA in the wood and soil, and the significantly lower moisture levels present in these sections.

    The validity of using the accelerated decay system to assess the performance of the four treated wood species is discussed.
    Date of AwardAug 1992
    Original languageEnglish
    Awarding Institution
    • Council for National Academic Awards
    SponsorsElectricity Council

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