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INTRODUCTION
LIME:
A white caustic alkaline substance consisting of calcium oxide, which is obtained by heating limestone and which combines with water with the production of much heat.
VARIETIES OF LIME
Shell lime:
• It is very pure lime obtained by calcination of shells of sea animals and corals.
• It is used for lime punning, whitewash and colour wash, soil stabilization and glass production
Stone lime:
• It is almost pure lime obtained by calcination of limestone and is used for making lime-sand mortar for superstructures, lime surkhi mortar for substructures and lime terracing.
Magnesium lime:
• It is manufactured from dolomite and contains magnesia more than 5%.
• It is used for making mortar and plaster
Kankar lime:
• It is an impure lime obtained by calculations of kantars dug out from underground sources.
• It is suitable for making lime sand mortar for substructures.
• It is commonly used for making hydraulic lime.
PURE, RICH OR FAT LIME
• This is known as fat lime because it increases 2 to 2.5 times in volume when soaked.
• This lime is obtained from burning pure limestone.
• This is also known as pure, rich, white, high calcium lime.
• This lime contains about 95% calcium oxide and 5% other materials inform of impurities.
• After burning when limestone containing mostly calcium carbonate is burnt in the atmosphere, carbon dioxide is driven out, leaving back calcium oxide known as quick lime.
• Fat lime is obtained by slaking quick lime.
• For setting, this lime absorbs carbon dioxide from the atmosphere and after chemical reaction gets converted into calcium carbonate which is quite hard substance insoluble in water.
• Setting and hardening of this lime is very low.
PROPERTIES OF FAT LIME:
• It hardens very slowly
• It has a high degree of plasticity
• It is soluble in water
• Its colour is perfectly white
USES OF FAT LIME:
• It is used in whitewashing and plastering walls.
• It is used for making lime-sand mortar for brickwork and stonework
• It is used for making lime-surkhi mortar for thick masonry walls, foundations. Etc.
HYDRAULIC LIME:
• It is obtained by moderate burning (900 – 1100 degree c) of raw limestone
• Raw limestone contains small proportions of clay 5-30% and iron oxide is a chemical combination with the calcium oxide content.
• In slaking considerable care must be required to provide just sufficient water since an excess of water would cause the lime to harden.
Depending upon the clay present in this lime, it is further classified into feebly, moderately and eminently hydraulic limes.
FEEBLY HYDRAULIC LIME:
• It contains silica and alumina or iron oxide less than 15%
MODERATELY HYDRAULIC LIME:
• It contains 15 to 25% silica and alumina.
EMINENTLY HYDRAULIC LIME:
• It contains 25 to 30% silica and alumina ingredients.
PROPERTIES OF HYDRAULIC LIME:
• It can set underwater
• It forms a thin plastic paste with water
• This lime is not perfectly white
• It contains 30% clay content
LEAN OR POOR LIME:
• It consists of calcium oxide and magnesium oxide 80 to 85% and clayey impurities of about more than 7% in the form of silica-alumina and iron oxide.
• Its sets on absorbing carbon dioxide from the atmosphere.
PROPERTIES OF POOR LIME:
• It hydrates slowly
• It makes a thin paste with water
• Setting and hardening is very slow.
• The colour varies from yellow to grey
PROPERTIES OF LIME:
• Lime possesses good plasticity and is easy to work with it.
• It stiffens easily and is resistant to moisture.
• It gives strength to the masonry when used as mortar
• It has good adhering properties with stone and bricks
• Its shrinkage is comparatively low and hence masonry in lime mortar is more durable.
USES OF LIME:
• It is used for whitewashing and for serving as a base coat for distemper.
• It is used in the production of glass
• It is used for the production of artificial stone, lime-sand brick, foam-silicate products etc.
• It is used as a flux in the metallurgical industry
• It is used as a matrix for concrete and mortar
• It is used as a chemical raw material in the purification of water and for sewage treatment.
• It is used for making mortar for masonry work.
• It is used as a refractory material for open-hearth furnaces
TIMBER
TIMBER:
Timber is a natural product, used for the construction of doors, windows, roofs, partitions, beams, posts, cupboards, shelves etc.
Characteristics of timber:
• It should have a uniform colour
• A freshly cut surface gives a sweet smell
• It should have annular rings
• It should have sonorous when stuck
• It should have straight and close fibres
• It should be heavy in weight
• It should be free from shakes, flaws, blemishes
• It possesses the property of elasticity
• It should be fire-resistant if the structure is very dense
• It should be hard and strong for structural uses.
Advantages of timber:
• Easy to handle, planed, saw, joined.
• Easy available and quick transport.
• Good insulator of heat and sound
• Since light weight-used in earthquake regions.
• Repairs, additions, alterations are easy.
• It resists corrosion, used in seawater or marine works.
Disadvantages of timber:
• Destroyed by decay induced by fungi.
• It swells and undergoes shrinkage with changing atmosphere.
• Built closely, serious conflagration hazard (fire)
Uses:
• It is generally used in the form of posts, beams, lintels, door-window frames and leaves, roof members.
• It is employed for flooring, ceiling, panelling and construction of partition walls.
• It is used for formwork for concrete.
• It is also used in making furniture, agricultural implements, sports goods, musical instruments, well curbs and carriages, railway sleepers, packing cases etc.
CLASSIFICATION OF TREES:
• Exogenous or outward growing trees
• Endogenous or inward growing trees
Exogenous tree:
It grows outwards and increases in bulk by the formation of successive annular rings on the outside under the bark.eg., deodar, teak wood etc.
Endogenous tree:
The tree grows inwards, too flexible, limited applications.eg. Bamboos, palms etc.
Endogenous trees are further divided into two types:
1) Hardwood
2) Softwood
Hardwood:
• It has broad leaves, dark colour, are generally dense and have narrow and well defined annular rings.
• It is capable of resisting all stresses equally well.
Softwood:
• Softwood has long and narrow pointed leaves.
• It is not capable of resisting all types of forces.
Factors affecting the strength of timber:
• Abnormalities of growth
• Way in which a timber piece is cut from the log.
• Faults in seasoning
• Moisture content
• Presence of knots shakes, etc.
• Invasion of insects, etc.
Seasoning of timber:
Seasoning of timber is a process of drying timber or removing moisture or sap, under more or less controlled conditions.
Objects of seasoning:
• To minimize the tendency of timber to shrink, warp and split.
• To increase strength and durability
• To maintain the shape and size
• To make timber safe from the attack of fungi, insects.
• To make fit to receive paints, preservatives, varnishes.
Advantages of seasoning:
• It decreases the weight of timber.
• It avoids defects appearing in timber.
• Improves the working qualities of timber.
• Increases the power in timber to held metal fasteners
Methods of seasoning:
1) Natural seasoning
2) Artificial seasoning
Natural seasoning:
i) Air-drying seasoning
ii) Water seasoning
Artificial seasoning:
i) Kiln seasoning
ii) Chemical seasoning
iii) Electrical seasoning
Air drying seasoning:
• Timber is stacked in a dry place about 30 cm above floor level.
• Arranged one upon another in longitudinal and cross pieces, leaving space for the free circulation of air.
• To protect from direct sunlight placed under a pitched roof covering.
• Cheap and simple method, but the seasoning needs 2 to 4 years.
• It requires large space to stack the timber.
• Very slow process extends over years.
Water seasoning:
• Logs of woods completely immersed in a running stream of water.
• By this time the sap, sugar, gum are leached out of the wood.
• The logs are taken out and left to dry in an open place.
• It is quick to process.
• As immersed in water causes more and regular drying, the tendency of wood to shrink or warp is reduced.
• The disadvantage it reduces the elasticity and durability of the timber.
• Boiling water seasoning reduces the strength, quick method and expensive process.
Artificial seasoning:
Kiln seasoning:
• It is adopted for rapid seasoning of timber on large scale to any moisture content.
• The scantlings are arranged for the free circulation of heated air with some moisture or super sulphated steam
• The circulating air takes up moisture required from wood and seasons it.
• The wood is immediately used.
• The timber is less liable to shrinkage.
• Moisture content can be reduced as per required
• Drying of different surfaces is even and uniform.
Chemical seasoning:
• Also called salt seasoning.
• Immersed in salt soluble solutions.
• Taken out and seasoned ordinarily.
Electrical seasoning:
• The logs are placed in such a way that their two ends touch the electrodes
• That the rise in temperature, the moisture gets evaporated
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