This document provides information about timber used in civil engineering. It defines timber, wood, and lumber. It classifies trees as endogenous or exogenous and describes types of wood. It discusses seasoning of timber, including natural, kiln, chemical, and electric methods. It also describes defects in timber like shakes and cracks. Methods to preserve timber include applying coal tar oils or zinc chloride. Preservatives can be applied by painting, pressure treatment, or empty cell processes.

2. Mehran University College of Engg: & Technology KhairpurMehran University College of Engg: & Technology Khairpur
Civil Engineering MaterialsCivil Engineering Materials
11stst
Term 1Term 1stst
Year B.E.CivilYear B.E.Civil

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TIMBER:
The wood which is
suitable or fit for
engineering construction
or engineering purpose
is called timber.

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WOOD:
The organic matter
obtained from trees is
called wood.

5. LUMBER:
The sawed wood meant
for construction in the
form of boards is called
lumber.

6. Structure of a Tree

7. TYPES OF TREES:
Trees are classified into two
groups depending upon
growth pattern.
(1) Endogenous trees:
The trees which grow inwards
in longitudinal fibrous mass
are called endogenous trees.

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(2) Exogenous tress :
The trees which grow in out wards
across horizontal section of stem
are called exogenous trees.
These trees are only fit for
engineering construction.
Exogenous trees are again
subdivided in to two types.

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Conifers or Evergreen:
They give soft wood.
They have pointed leaves.
Examples:
Deodar
Pine
Chir
Kail,etc

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Deciduous:
These have hard wood.
These have broad leaves.
Examples:
Teak
Sal
Shisham, etc.

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SEASONING OF TIMBER:
As fresh timber which is obtained
from trees contains about 30 to 40
% sap or moisture. This sap is very
harmful for the life of a timber.
Therefore, it is necessary to remove
that sap by applying some special
methods. All those methods which
are used for removing the sap from
timber are collectively termed as
seasoning of timber.

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Advantages of seasoned timber:
It has reduced weight,
It is strong and durable,
It has resistance to decay or rot,
It takes high polish,
It is easier to work,
Its life is more.

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Types of Timber Seasoning:
The main types of timber seasoning are
as under.
(1)Natural Seasoning,
(2)Artificial Seasoning,
(a) Kiln Seasoning,
(b) Chemical Seasoning,
(c) Electric Seasoning,
(3) Water Seasoning,

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(1) Natural Seasoning:
In the air seasoning or natural seasoning or
natural drying, seasoning of timber, timber
is dried by direct action of air, wind and
sun. In this method, the timber logs are
arranged one over the other, keeping some
space or distance between them for air
circulation of fresh air.
Generally this type of seasoning requires
few months to over a year, this is very slow
process.

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16. (2) ARTIFICIAL SEASONING
(a) Kiln Seasoning,
(b) Chemical Seasoning,
(c) Electric Seasoning,
Developed by:G.S.Solangi 16

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(a) Kiln Seasoning:
In kiln seasoning timber is placed in a
chamber with some special heating
arrangement.
In this process one thing should be
kept in mind that heating system
should be under control, other wise
timber will be crack or wrap. The time
required for this seasoning is 3 to 12
days. This is quick process.

18. Kiln Seasoning
18

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(b) Chemical Seasoning:
In chemical seasoning carbon
dioxide, ammonium carbonate or
urea are used as agents for
seasoning, those are applied in dry
state, the inter surface of timber
dries first than outer side.
This ensures uniform seasoning.
The time required for this
seasoning is 30 to 40 days.

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(c) Electric Seasoning:
In this method electric current
is passed through the timber
logs. The time required for this
seasoning is 05 to 08 hours.

21. Electric Seasoning
Developed by:G.S.Solangi 21

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(3) Water Seasoning:
In water seasoning, timber logs are
kept immersed whole in the flowing
water. The sap present in timber is
washed away. After that logs are
taken out from water and are kept
in open air, so water present in
timber would be dried by air. The
time required for this type of
seasoning is 2 to 4 weeks.

23. Prepared by:G.S.Solangi
USES OF TIMEBR:
Timber is used in:
1.Building construction,
2.Construction of house posts,
3.Construction of beams,
4.Construction of rafters,
5.Construction of bridges,
6.Construction of piles, poles and
railway sleepers,
Continued--------

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7. For furniture making,
8. For light packing cases,
9. For high packing cases (for
machinery and similar stores),
10.For manufacturing of agricultural
implements,
11.For making toys, etc,
12.For manufacturing of veneers and
ply woods.

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VENEER:
Thin sheet of uniform thickness of
wood is called veneer.
PLYWOOD:
Veneers used for making plywood are
known as plies and ply wood is made
by gluing together plies in odd
numbers. Gluing is done under
pressure.

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DEFECTS IN TIMBER:
Most common defects in timber are:
1. Heart Shakes
2. Star Shakes
3. Cup Shakes
4. Radial Shakes
5. Rind Galls
6. Wind Cracks
7. Knots
8. Dead Wood

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(1) Heart Shakes:
These are splits occurring in the centre of the
tree and running from the pith (inner most
part) to wards the sap wood from the
medullary (vascular tissues) rays.
In some timbers, these splits are hardly visible
and in some timbers these are quite
permanent.
Heart shakes are caused due to shrinkage of
interior parts due to age. A heart shake
straight across the trunk is not a serious
defect.

28. Heart Shakes

29. Medullary Rays:
These are thin horizontal veins
radiating from the pith to wards the
bark. These carry sap from outer side
to inner side.

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(2) Star Shakes:
These are splits which radiate from
the centre of the timber or from the
bark (outer side), running in the
planes of medullary rays.
These occur due to severe frost or
scorching heat of the sun.

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(3) Cup Shakes:
These are curved splits which
separate the whole or part of one
annual ring from an other. These
are caused due to the unequal
growth of the timber.

33. Cup Shakes

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(4) Radial Shakes:
These are similar to the star
shakes and occur in felled timber
when exposed to the sun during
seasoning.
Radial shakes are generally
irregular, fine and numerous.
In this many splits are appeared.

35. Radial Shakes

36. Radial Shakes

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(5) Rind Galls:
These are typical enlarged
swellings and occur due to
branches cut-off.

38. Rind Galls

39. Rind Galls

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(6) Wind Cracks:
These are shakes or splits
on the sides of a bark of
timber due to shrinkage of
exterior surface exposed to
atmospheric influence.

41. Wind Cracks

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(7) Knots:
These are the roots of the small
branches of the tree. These are not
harmful.

43. Knots

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(8) Dead Wood:
It is the deficient in strength
and weight and is the result
of trees being felled after
maturity.

45. Dead Wood

46. DETERIORATION OF
TIMBER
(OR)
DECAY OF TIMBER:
46

47. DETERIORATION OF TIMBER
(OR)
DECAY OF TIMBER:
There are so many agencies which
may cause decay of timber. But there
are three main harmful agencies
which cause timber decay.

48. (1) Decay or Rot:
Decay or rot of timber is the result of
the activity of various bacterias and
fungi, which utilize various portions
of timber as food; they require both
oxygen and excess moisture. Hence
timber having moisture content
below 25 % will not rot easily.

49. (2) Insects:
There are so many insects
which attack the wood, out of
them termites (white ants) are
the main insects which are very
dangerous for timber. Termites
of one class live under ground
and eat wood and forms tubes
or tunnels inside it.

50. (3) Fire:
Fire is also the damaging
factor for timber. As timber
has tendency to burn, so fire
can damage it easily.

51. PRESERVATION
OF
TIMBER
51

52. TIMBER PRESERVATIVES:
There are three main classes of timber
preservatives.
(1) Oily substances insoluble in water
(2) Water soluble salts

53. (1)Oily substances insoluble
in water:
Coal tar oil is the best known and
widely used preservative material of
this class. It is obtained during the
destructive distillation of bituminous
coal. It is available in many grades and
types. It has high degree of penetration.
It has highly toxic effect to wood
destroying fungi.

54. (2) Water soluble salts:
Zinc chloride is the most extensively
used preservative of this type. It is
clean and odourless.

55. SPECIAL PAINTS TO SAVE TIMBER
FROM FIRE:
Following paints are used to save
timber from fire.
Diammonium phosphate,
Mono ammonium phosphate,
Mono magnesium phosphate,
Phosphoric acid.

56. METHODS OF APPLYING
PRESERVATIVES:
Before applying preservatives, the
timber should be completely seasoned.
There are some important methods of
applying timber preservatives which are
given below.
1.Painting and dipping method
2.Pressure process or full cell process
3.Empty cell process

57. (1) Painting and dipping method:
This is the most common method in
which the preservative material is
applied by means of a brush several
times. The timber is also immersed in a
tank full of liquid (preservative material).
In both types the penetration hardly
exceeds 1/16’’. The duration of
immersion and temperature of solution
is increased the penetration rate.

58. (2) Pressure process or full cell process:
In this process, the timber is placed in an air
tight chamber, from which air is with drawn
by creating a vacuum. The cells are full
emptied to receive preservative material.
After that preservative material is pumped
under pressure of 100 to 200 psi and at a
temperature of 120degreeF. As the timber
contains required quantity of preservative a
low vacuum is maintained to remove excess
preservative. Such a timber is generally
used in case of piles in salt water and
railway sleepers.

59. (3) Empty cell process:
This method is similar to the full cell
process but initial vacuum is not to
be maintained and no attempt is to
be made to remove the air from
cells. The preservative material is
applied under pressure of 200 psi.

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