Presentation on theme: "Durability- Natural Durability Biological/ Physical Hazards Weathering Fire Chemical TIMBER Species Natural durability of heartwood Maintenance ensures."— Presentation transcript:
Durability- Natural Durability Biological/ Physical Hazards Weathering Fire Chemical TIMBER Species Natural durability of heartwood Maintenance ensures protection remains functional Treatment enhances durability of sapwood Fungi Termites / borers Marine Design Detailing minimises exposure to hazards
Natural Durability l Measure of resistance of heartwood (older wood) to fungal or insect attack l Used when selecting a species for a specific function n Can match the hazard with natural durability and avoid the use of treated timber n If can’t find readily available timber with appropriate ND, use a treated timber product l Measured by field trials in which small samples are driven into the ground at different sites around Australia. Regularly inspected for signs of decay or attack
Natural Durability l Different for different species n Different natural chemicals (extractives) stored in wood as a by-product of growth. n Some extractives are toxic to fungi and insects n Different cell structures in different species allow some insects to breed in the cells. Other species will not accommodate their eggs l Find ND for Australian species in AS5604:2003 (also in AS1720.2.)
Natural Durability (Sapwood) All sapwood has low natural durability l Starches transported in the sap are very attractive to all fungi and most insects.
Natural Durability (Heartwood) Extractives and growth characteristics affect natural durability of timber species ClassDurabilitySpecies 1 Highly durableIronbark, Tallowwood, Cypress, Turpentine, Forest red gum 2 DurableSpotted gum, Blackbutt, River red gum, Western Cedar, Stringybark (yellow & white) 3 Moderately durable Brush box, Rose/flooded gum, Sydney blue gum, Silver topped stringy bark 4 Non-durableDouglas fir, Hoop pine, Radiata pine, Mountain ash/ Tasmanian oak, Unidentified timbers Blackbutt Tallowood Tasmanian Oak Sydney blue gum
Long-term Performance of Timber Can match natural durability class with environmental hazard to estimate long-term performance of untreated timber heartwood Natural Durability Class Heartwood Service Life (years) H1 fully protected H3 Above ground exposed H5 in-ground Class 150 + 25 + Class 250 +3015 – 25 Class 350 +158 – 15 Class 450 +5 - 8< 5
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