DURABILITY OF TIMBERS

DURABILITY OF TIMBERS : 

DURABILITY OF TIMBERS PRESENTED BY N.KANAGARAJ BSF-06-007 BSC [FORESTRY]

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CONTENTS Durability –definition chief causes of non durability Classification Classification based on the durability in marine conditions Classification of wood in order of durability Factors affecting durability of timber Causes of natural durability

Natural durability “Natural durability is the broad term used to define the resistance of wood in its natural form to the combined effects of decay or rot” orthe resistance to bio degradation is termed as Natural durability : 

Natural durability “Natural durability is the broad term used to define the resistance of wood in its natural form to the combined effects of decay or rot” orthe resistance to bio degradation is termed as Natural durability Durability is meant the property of wood remain sound It is also described as the measure of time during which wood remains unaffected by fungi ,insects or other destroying agents Durability -definition

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From utilization point of view durability is very necessary such as construction of house buildings railway sleepers ship building The durability is of course most variable and differences are found not only in the same species growing in different areas but also with in trees

Sapwood Sapwood of most species has little durability because there are no extractives contained in the wood, and it is laden with starches (normally intended for the growth of the tree, but also essential for the growth of fungi). : 

Sapwood Sapwood of most species has little durability because there are no extractives contained in the wood, and it is laden with starches (normally intended for the growth of the tree, but also essential for the growth of fungi). Heartwood   The resistance of a particular species to attack from fungi and termites is determined by the type of extractives stored in the heartwood

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The chief causes of non durability of wood is Fungi Insects Animals Mechanical wear and tear

Fungi : 

Fungi Fungi are the worst enemy of wood They gain admittance by means of spores and germinate in the wood cell and send out minute filaments-Hypae Action- reduces wood to soft spongy mass of disintegrated wood tissues. The commonest are Trametes pinii, Ganoderma lucidum, polyporous gilvus and polyporous shoreae

Insects : 

Insects Reduces the durability of wood Worst of these are termites (white ants) These insects destroy the wood by eating softer timber and cell content The others are-borers, beetles which do often as much harm as termite Eg. Bostrychidae, cerambycidae , Buprestidae, Scolytidae and platypodidae

Termites : 

Termites Dry wood termite Termite nest

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Gallery Carpenter ants damage

Animals : 

Animals Amongst wood destroying animals, the marine molluscs and crustaceans are the most serious They are found in the brackish water in harbours and river mouths, Wooden piers and marine structure are often completely destroyed by these animal crustaceans

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molluscs

Mechanical wear and tear : 

Mechanical wear and tear The use to which the timber is put, results in course of time, in its wearing off due to mechanical fracture and abrasion. Although not natural agents, they are nevertheless important in the life of timber.

Durability types : 

Durability types Three types of durability is found durability by design durability by nature durability by treated wood

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durability by design design the building to protect the wood elements, keep wood dry during construction, and practice good maintenance of the building. This approach is called durability by nature Select the species which are naturally durable Durability by treatement Most of our construction lumber is not naturally durable, but we can make it decay resistant by treating it with a preservative. Preservative-treated lumber is more reliably resistant to decay than naturally durable lumber p

Classification in the field test , stake samples from heartwood portion are placedin the ground , half buried and half exposed to the atmosphere and there condition is inspected periodically : 

Classification in the field test , stake samples from heartwood portion are placedin the ground , half buried and half exposed to the atmosphere and there condition is inspected periodically Class 1: Timbers of the highest natural durability. Class 2: Timbers of high natural durability. Class 3: Timbers of only moderate durability . Class 4: Timbers of low durability. These timbers have about the same durability as untreated sapwood, which is generally regarded as Class 4, irrespective of species spp

IN USA and some other countries the above classification is done in five categories i.e : 

IN USA and some other countries the above classification is done in five categories i.e Perishable, non durable moderately durable, durable and very durable

Non durability of wood in marine water : 

Non durability of wood in marine water Resistance to sea animals is spectacularly low as compared to resistance to land pest But some shows useful resistance under marine condition E.g Xylia dolabriformis, Tectona gradis, Eucalyptus marginata and acacia catechu Lignum vitae and ocotea rodiaei most durable foreign wood species

Classification based on the durability in marine conditions : 

Classification based on the durability in marine conditions Class I- Life >5 years Anogeissus latifolia, Dipterocarpus indicus Lagerstroemia microcarpa Tectona grandis Terminalia alata Xylia Xylocarpa Pterocarpus dalbergioides Class II- b/w 3 to 5 years Callophyllum sp. Hopea parviflora Mesua ferrea Pterocarpus marsupium

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Class III- < 3 year Abies pindrow, bombax ceiba Bombax insigne, Albizia spp. Shorea robusta Mimusops spp. Terminalia paniculata Chukrasia tabularis The species which proved very durable on land did not survive more than 8 years in Sea waters. Thus durability on land has no direct relation to durability in sea waters.

Classification of wood in order of durability : 

Classification of wood in order of durability The trials for durability carried out in FRI Dehradun constitute a record of untreated timbers, and on the basis of the important species have been classified as under Extremely durable- Very durable Durable Fairly durable Slightly durable Perishable

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Extremely durable- Acacia catechu, Mesua ferrea, Tectona gradis, sylia doabriformis, Hardwickia binata Very durable Artocarpus lakoocha, Cedrus deodera, Cupressus torulosa, Dalbergia latifolia, Dalbergia sissoo, Hopea spp. Shorea robusta Durable Acacia nilotica, Adina cordifolia, Albizia spp. Syzygium cuminii, Ougeinia oojeinensis, Pinus wallichiana, Terminlia alata

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Fairly durable Anogeissus latifolia, Toona ciliata, Mangifera indica, Picea smithiana, Abies pindrow, Quercus spp. Terminalia belerica, Terminalia chebula Slightly durable Bombax ceiba, butea monosperma, Trewia nudiflora Prishable Dalbergia paniculata, Sapium insigne, Sterculia spp.

Factors affecting durability of timber : 

Factors affecting durability of timber Moisture content Specific gravity and hardness Presence of resins and oils in wood Use of wood

Moisture content : 

Moisture content The presence of sap reduces the durability of wood Hence sapwood is less durable than heartwood The actual moisture content of the wood is also and important factor in the case of fungus attack Well seasoned wood is less subject to fungus attack

Specific gravity and hardness : 

Specific gravity and hardness Heavier and harder wood are durable Hardness repels the attack of insects and borers and increases the durability of wood Presence of resins and oils in wood The content and exudations of wood cells, affect durability considerably and the presence of toxic substances such as oils, gums and resins keep away fungi and insects.

Use of wood : 

Use of wood The use to which the timber is put determines its durability. Wood used in a dry location is not liable to decay. Wood indefinitely kept submerged in water does not rot. Wood embedded in the ground decays rapidly and the presence of organic matter in the soils encourages its decay Wood lying on the ground and damp places with littlie air circulation is liable to decay and rot rapidly

Causes of natural durability of wood : 

Causes of natural durability of wood Extractives are responsible for durability of heartwood in some species The extractives are mostly phenolic in nature or terpenes The effectiveness is determined by Amount present Type Chemical stability Resistance to depletion by leaching, microbial degradation, volatilization

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Thank you