Suitability of using plantation-grown Nauclea diderrichii Merill poles for electricity and telecommunication overhead support lines in Ghana - Part 2: Treatability

One hundred and sixty four (1 64) poles of plantation-grown Kusia (Nauclea diderrichii Merill) of lengths 8 to 13m extracted from the Pra-Anum Forest Reserve in Ghana were kiln-dried and then treated by the full cell vacuum-pressure impregnation method until 'refusal' with a copper-chrome-arsenate wood preservative. The depths of penetration were measured and preservative retention analysed by X-ray fluorescence spectroscopy. Mean sapwood penetration was 91-103% of the sapwood width (30.9 - 52.9 mm). The total oxides retentions (23. 75 to 24.81 kg/m3) in an assay zone of 0-25 mm were higher than the recommended retention of 20 kg/m3. The preservative oxides balance in the treated poles indicated some disproportionation, with slight differential fixation of the Cr03 at the expense of the As2O5 components. It is recommended that the minimum sapwood width be limited to 25 mm; and that 85-100% sapwood penetration be achieved during treatment. An assay zone of 0-25 mm is recommended. The treatability
properties of Kusia render it particularly suitable for use as 8-13 m long poles for high voltage electric transmission and distribution support lines.