Adequate preservative treatment of tropical and subtropical hardwoods for electric anchor logs
A K Lahiry
Most available 27 different hardwood species grown in Bangladesh was investigated regarding suitability as CCA-C (chromated copper arsenate type-C) impregnated anchor logs for rural electrification programme. The kiln-drying properties, sapwood thicknesses, CCA treatability grades of sapwood and heartwood, natural durability of heartwood and CCA retainability at specific assay zone separated 27 hardwoods into two different treatment groups A and B. The logs of both the groups were full cell pressure treated at initial vacuum of 600-700 mm Hg and at impregnation pressure of 14-18 kg/cm2. The logs are equivalent regarding service life. The treatment group A includes 7 species, characterized by pretreatment moisture content of 15%, thin sapwood thickness of at least 25 mm, high natural durability and refractory to treatment of heartwood, penetration requirement of at least 25 mm plus 100% sapwood with treatment grades of 75% (+++) and retention requirement of 20 kg/m3 dry oxides in an assay zone of 5-25 mm. The treatment group B includes 20 species, characterized by pretreatment moisture content of 20% thicknesses of sapwood and treatable wood equivalent to at least 44% of radius of logs, low natural durability of heartwood, penetration requirement of at least equivalent to 44% of radius of logs plus 100% sapwood with treatment grades of 75% to 100% (+++ to ++++) and retention requirement of 20 kg/m3 dry oxides in an assay zone of 12-50 mm.