Transcript The Time Value of Money

1
WHAT IS CONCRETE?
 Construction material
 Mixture of portland cement, water, aggregates,
and in some cases, admixtures.
 The cement and water form a paste that hardens
and bonds the aggregates together.
 Often looked upon as “man made rock”.
 Versatile construction material, adaptable to a wide variety of
agricultural and residential uses.
 Strong, durable, versatile, and economical.
http://www.inlandcanada.com/NR/rdonlyres/F0EBC912-01A0-4D58-AE7D6F9FD7DE0FF7/0/ConcreteRecycler3.jpg
CONCRETE
CONCRETE
 Can be placed or molded into virtually any shape and
reproduce any surface texture.
 The most widely used construction material in the world.
 In the United States almost twice as much concrete is used as
all other construction materials combined.
 The ready-mix concrete producer has made concrete an
appropriate construction material for many applications.
Composition of concrete
 Water
 Aggregates
 Chemical admixtures
 Cement
http://www.bu.edu/sjmag/scimag2008/images/Texture__Concrete_Crac
ked_by_ivelt_resources.jpg
WATER
 Good water is essential for quality concrete.
 Should be good enough to drink--free of trash, organic matter and
excessive chemicals and/or minerals.
 The strength and other properties of concrete are highly dependent
on the amount of water and the water-cement ratio.
http://pure-perfection.net/custom/Water-Droplet-1039X761.jpg
AGGREGATES
 Aggregates occupy 60 to 80 percent of the
volume of concrete.
 Sand, gravel and crushed stone are the
primary aggregates used.
 All aggregates must be essentially free
of silt and/or organic matter.
http://www.bondedaggregate.co.uk/images/select-aggregatedriveway.jpg
CHEMİCAL ADMİXTURES
 Materials in the form of powder or fluids that are added to
the concrete to give it certain characteristics not obtainable
with plain concrete mixes.
 In normal use, admixture dosages
are less than 5% by mass of cement,
and are added to the concrete at the
time of batching/mixing.
CHEMİCAL ADMİXTURES
The most common types of admixtures are:
 Accelerators :
- Speed up the hydration (hardening) of the concrete.
- Typical materials used are CaCl2 and NaCl.
 Acrylic retarders :
-Slow the hydration of concrete, and are used in large or
difficult pours.
- Typical retarder is table sugar, or sucrose (C12H22O11).
CHEMICAL ADMIXTURES
 Air Entraining agents:
-The most commonly used admixtures for agricultural
concrete.
-Produce microscopic air bubbles throughout the concrete.
-Entrained air bubbles:
 Improve the durability of concrete exposed to
moisture and freeze/thaw action.
 Improve resistance to scaling from deicers and
corrosive agents such as manure or silage.
CHEMICAL ADMIXTURES
 Water-reducing admixtures
-Increase the workability of plastic or "fresh" concrete,
allowing it be placed more easily, with less consolidating
effort.
-High-range water-reducing admixtures are a class of
water-reducing admixtures
 Increase workability
 Reduce the water content of a concrete.
 Improves its strength and durability characteristics.
REINFORCEMENT
 Strong in compression, as the aggregate
efficiently carries the compression load.
 Weak in tension as the cement holding the
aggregate in place can crack, allowing the
http://www.eurocode2.info/images/rein
forcement.jpg
structure to fail.
 Reinforced concrete solves these problems by
adding either metal reinforcing bars, steel fibers,
glass fiber, or plastic fiber to carry tensile loads.
CEMENT
 Crystalline compound of calcium silicates and other calcium
compounds having hydraulic properties.
 Considered hydraulic because of their ability to set and harden
under or with excess water through the hydration of the
cement’s chemical compounds or minerals
http://img.alibaba.com/photo/11654315/Portland_Cement_42_5_N_R.jpg
CEMENT
 Uses
Main use is in the fabrication of concrete and mortars
 Modern uses
-Building (floors, beams, columns, roofing, piles, bricks,
mortar, panels, plaster)
-Transport (roads, pathways, crossings, bridges, viaducts,
tunnels, parking, etc.)
-Water (pipes, drains, canals, dams, tanks, pools, etc.)
-Civil (piers, docks, retaining walls, silos, warehousing,
poles, pylons, fencing)
-Agriculture (buildings, processing, housing, irrigation)
CEMENT

HYDRAULIC CEMENTS:
 Hydraulic lime: Only used in specialized mortars. Made
from calcination of clay-rich limestones.
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Natural cements: Misleadingly called Roman. It is made
from argillaceous limestones or interbedded limestone and clay
or shale, with few raw materials. Because they were found to
be inferior to portland, most plants switched.
 Portland cement: Artificial cement. Made by the mixing
clinker with gypsum in a 95:5 ratio.
CEMENT

Portland-limestone cements: Large amounts (6% to
35%) of ground limestone have been added as a filler to a
portland cement base.
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Blended cements: Mix of portland cement with one or
more SCM (supplementary cemetitious materials) like
pozzolanic additives.

Pozzolan-lime cements: Original Roman cements. Only a
small quantity is manufactured in the U.S. Mix of pozzolans
with lime.
CEMENT

Masonry cements: Portland cement where other materials
have been added primarily to impart plasticity.

Aluminous cements: Limestones and bauxite are the main
raw materials. Used for refractory applications (such as
cementing furnace bricks) and certain applications where rapid
hardening is required. It is more expensive than portland. There
is only one producing facility in the U.S.
PORTLAND CEMENT
 Most active component of concrete
 The greatest unit cost in concrete,
 Its selection and proper use are
important in obtaining most
economically the balance of
properties desired for any particular
concrete mixture.
http://www.cement.org/decorative/images/overview
2.jpg
PORTLAND CEMENT
 The production process for portland cement first involves
grinding limestone or chalk and alumina and silica from shale
or clay.
 Type I/II portland cements are the most popular cements used
by concrete producers
-Type I cement is the general purpose cement and most
common type. Unless an alternative is specified, Type I is
usually used.
-Type II cement releases less heat during hardening. It is
more suitable for projects involving large masses of concrete-heavy retaining walls
Types of Portland cement
Cement
type
Use
I1
General purpose cement, when there are no extenuating
conditions
II
Aids in providing moderate resistance to sulfate attack
III
When high-early strength is required
IV
When a low heat of hydration is desired (in massive structures)
V
When high sulfate resistance is required
IA
A type I cement containing an integral air-entraining agent
IIA
A type II cement containing an integral air-entraining agent
IIIA
A type III cement containing an integral air-entraining agent
PORTLAND CEMENT
Physical Properties of Portland Cements
1) Fineness,
2) Soundness
3) Consistency
4) Setting time
5) Compressive strength
6) Heat of hydration
7) Loss of ignition
Concrete production
 This process develops physical and chemical properties like
mechanical strength, low moisture permeability, and chemical
and volumetric stability.
A properly proportioned concrete mix will provide
 Mixing concrete
 Workability
 Curing
Mixing concrete
 Essential for
The production of uniform concrete,
II. High quality concrete.
 Equipment and methods should be capable
of effectively mixing
I.
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Workability
 The ease with which freshly mixed concrete can be placed and
finished without segregation.
 Difficult to measure but ready-mix companies usually have
experience in determining the proper mix.
 Important to accurately describe what the concrete is to be used
for, and how it will be placed.
Curing
 Concrete that has been specified, batched, mixed, placed, and
finished "letter-perfect" can still be a failure if improperly or
inadequately cured.
 Usually the last step in a concrete
project and, unfortunately,
is often neglected even by professionals.
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Curing
 Curing has a major influence on the properties of hardened
concrete such as durability, strength, water-tightness, wear
resistance, volume stability, and resistance to freezing and
thawing.
 Proper concrete curing for agricultural and residential
applications involves keeping newly placed concrete moist and
avoiding temperature extremes (above 90°F or below 50°F) for
at least three days.
 A seven-day (or longer) curing time is recommended.
Curing
 The best curing method depends on:
 Cost,
 Application equipment required,
 Materials available,
 Size and shape of the concrete surface.
 Prevent the loss of the mixing water from concrete by sealing
the surface.
 Can be done by:
 Covering the concrete with impervious paper or plastic
sheets,
 Applying membrane-forming curing compounds.
Curing
 Begin the curing as soon as the concrete has hardened
sufficiently to avoid erosion or other damage to the freshly
finished surface.
 Usually within one to two hours after placement and finishing.
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Properties of concrete
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Strength
Elasticity
Cracking
Shrinkage cracking
Tension cracking
Strength
Concrete has relatively
 High compressive strength,
 Low tensile strength
 Fair to assume that a concrete sample's tensile strength is about
10%-15% of its compressive strength
 The ultimate strength of concrete is influenced by
- water-cementitious ratio
-the design constituents
- the mixing
-placement
-curing methods
Elasticity
 Function of the modulus of elasticity of the aggregates and the
cement matrix and their relative proportions
 The American Concrete Institute allows the modulus of elasticity
to be calculated using the following equation:
where
wc = weight of concrete (pounds per cubic foot) and where
f'c = compressive strength of concrete at 28 days (psi)
Cracking
 All concrete structures will crack to some extent.
 Cracks due to tensile stress induced by shrinkage or stresses
occurring during setting or use
Shrinkage cracking
 Occur when concrete members undergo
restrained volumetric changes (shrinkage)
as a result of either drying, autogenous
shrinkage or thermal effects.
 The number and width of shrinkage
cracks that develop are influenced by
-the amount of shrinkage that occurs
-the amount of restraint present
-the amount and spacing of reinforcement
provided.
http://epg.modot.org/files/thumb/3/39/216_Remo
val_of_existing_expansion_joint.jpg/550px216_Removal_of_existing_expansion_joint.jpg
Tension cracking
 Most common in concrete beams where a transversely applied
load will put one surface into compression and the opposite
surface into tension due to induced bending.
 The size and length of cracks is dependent on
- The magnitude of the bending moment
- The design of the reinforcing in the beam at the point
under consideration.
Types of concrete
 Regular concrete

 High-strength concrete
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 Stamped concrete
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 High-performance concrete
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 Self-consolidating concretes
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 Vacuum concretes
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 Shotcrete
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 Pervious concrete
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 Cellular concrete,
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 Cork-cement composites
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 Roller-compacted concrete

Glass concrete
Asphalt concrete
Rapid strength concrete
Rubberized concrete
Polymer concrete
Geopolymer or green concrete
Limecrete
Refractory Cement
Concrete cloth
Innovative mixtures
Gypsum concrete
Concrete testing
Compression testing of a concrete cylinder
http://www.antouncivil.com.au/vca/Images/testing.jpg
Same cylinder after failure
http://www.concrete-curb.com/wpcontent/uploads/BreakageCylinder.jpg
General test methods
 Compaction Factor Test (Compacting Factor Test, Glanville)
 Compaction Test
 Free Orifice Test (Orimet Test)
 K-Slump Tester
 Free Flow Test Methods
 Slump Test
 Modified Slump Test
 Slump Rate Machine
 Kelly Ball Test
 Ring Penetration Test
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Cone Penetration Test
Moving Sphere Viscometer
Flow Trough Test
Delivery-Chute Torque Meter
Delivery-Chute Depth Meter
Surface Settlement Test
Concrete recycling
 increasingly common method of disposing of concrete
structures
 recycling is increasing due to
-improved environmental awareness
- governmental laws
-economic benefits
 Recycling concrete provides
-environmental benefits
-conserving landfill space
Construction materials
 Asphalt
 Aggregate
 Brick
 Gypsum
ASPHALT
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Also known as bitumen
Dark brown to black
Highly viscous
Hydrocarbon produced from petroleum
distillation residue.
 At least 80% carbon, which explains its
deep black color.
 Sulphur is another ingredient.
 Primarily used as a sealant for rooftops
and a durable surface for roads, airport
runways, playgrounds and parking lots.
http://www.ekocozum.com/blog/wpcontent/uploads/2008/05/asfalt.jpg
the other components in crude
oil
 By the process of fractional
distillation, usually under
vacuum conditions.
http://www.cranedigital.com/case_studies/oil_and_gas/fractional_distillation_column2.jpg
ASPHALT
 Asphalt can be separated from
TYPES OF ASPHALT
 The major types of asphalt
http://www.pkeenanroads.com/wp-content/gallery/stone/rolled.jpg
http://www.highwaysmaintenance.com/JPEGsurf/smisSMA.jpg
used in construction are ;
 Rolled asphalt
 Mastic asphalt.
Rolled Asphalt
 Made of aggregate, or solid materials such as sand, gravel, or
recycled concrete, with an asphalt binder.
 Used to make roads and other surfaces, such as parking lots,
by being applied in layers and compacted.
 Different types of rolled asphalt are distinguished according to
the process used to bind the aggregate with the asphalt.
TYPES OF ROLLED ASPHALT
 Hot mix asphalt concrete
(HMAC)
- Produced at 160 degrees
Celsius.
-This high temperature serves
to decrease viscosity and
moisture during the
manufacturing process,
resulting in a very durable
material.
-HMAC is most commonly
used for high-traffic areas,
such as busy highways and
airports.
http://www.crossroadspaving.com/images/asphalt-paving-repair.jpg
ROLLED ASPHALT
 Warm mix asphalt concrete
(WAM or WMA)
-Reduces the temperature
required for manufacture by adding
asphalt emulsions, waxes, or
zeolites.
-Benefits both the environment
and the workers, as it results in less
fossil fuel consumption and reduced
emission of fumes.
http://www.wispave.org/images/iStock_000007064664XSmall.jpg
ROLLED ASPHALT
 Cold mix asphalt concrete,
-Emulsified in soapy water before
mixing it with the aggregate,
eliminating the need for high
temperatures altogether.
-The asphalt produced is not
nearly as durable as HMAC or WAM
-Typically used for low traffic
areas or to patch damaged HMAC.
http://www.dykespaving.com/wp-content/themes/classic/images/coldmix.jpg
ROLLED ASPHALT
 Cut-back asphalt concrete
-Illegal
in the United states since the 1970s, but many other
countries around the world still use it.
-The least environmentally friendly option, resulting in
significantly more air pollution than the other forms.
-Made by dissolving the asphalt binder in kerosene
beforemixing it with the aggregate, reducing viscosity
while the concrete is layered and compacted.
MASTIC ASPHALT
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
Also called sheet asphalt.
Lower bitumen content than the rolled asphalt.
Used for some roads and footpaths.
Used also in roofing and flooring
.
http://www.e470.com/images/newsSMAfullsized.jpg
MASTIC ASPHALT
 Stone mastic asphalt (SMA), is another variety.
 Becoming increasingly popular as an alternative to rolled
asphalt.
 Benefits include
-Anti-skid property
-The absence of air pockets
But if laid improperly
-May cause slippery road conditions.
PHYSICAL PROPERTIES OF
ASPHALT
 Durability
- A measure of how asphalt binder physical properties
change with age.
- Sometimes called age hardening
.
- In general, as an asphalt binder ages, its viscosity increases
and it becomes more stiff and brittle.
PHYSICAL PROPERTIES OF
ASPHALT
 Rheology
 The study of deformation and flow of matter.
 Deformation and flow of the asphalt binder in HMA is
important in HMA performance.
 HMA pavements that deform and flow too much may be
susceptible to rutting and bleeding, while those that are too stiff
may be susceptible to fatigue cracking.
PHYSICAL PROPERTIES OF
ASPHALT
 Safety
 Asphalt cement like most other materials, volatilizes (gives off
vapor) when heated.
 Flash point.
 For safety reasons, the flash point of asphalt cement is tested
and controlled.
 Purity.
 Asphalt cement, as used in HMA paving, should consist of
almost pure bitumen.
 Impurities are not active cementing constituents and may be
harmful to asphalt performance.
AGGREGATE
 Collective term for sand, gravel and crushed stone mineral
materials in their natural or processed state
 Roads and highways constitute the largest single use of
aggregate at 40 percent of the total
AGGREGATE ORIGINS AND PRODUCTION
 Can either be natural or manufactured
I.
II.

Natural aggregates are generally extracted from larger rock
formations through an open excavation
Manufactured rock typically consists of industrial
byproducts such as slag (byproduct of the metallurgical
processing – typically produced from processing steel, tin
and copper)
Specialty rock that is produced to have a particular physical
characteristic not found in natural rock (such as the low
density of lightweight aggregate).
AGGREGATE PHYSICAL PROPERTIES
 Toughness and abrasion resistance. Aggregates should be
hard and tough enough to resist crushing, degradation and
disintegration from activities such as manufacturing,
stockpiling, production, placing and compaction.
 Durability and soundness. Aggregates must be resistant to
breakdown and disintegration from weathering
(wetting/drying) or else they may break apart and cause
premature pavement distress.
 Particle shape and surface texture. Particle shape and
surface texture are important for proper compaction, load
resistance and workability. Generally, cubic angular-shaped
particles with a rough surface texture are best.
 Specific gravity. Aggregate specific gravity is useful in
making weight-volume conversions and in calculating the void
content in compacted Hot Mixed Asphalt
 Cleanliness and deleterious materials. Aggregates must be
relatively clean when used in HMA. Vegetation, soft particles,
clay lumps, excess dust and vegetable matter may affect
performance by quickly degrading, which causes a loss of
structural support and/or prevents binder-aggregate bonding
GYPSUM
 Occurs in nature as :
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- flattened
- often twinned crystals
- transparent cleavable masses
called selenite.
May also occur in a silky, fibrous
form, in which case it is commonly
called satin spar.
Finally may also be granular or quite
compact.
In hand-sized samples.
Can be transparent or opaque.
http://www.warmtec.co.nz/mediac/400_0/media/variotherm3.JPG
 A common mineral, with thick
and extensive evaporite beds in
association with sedimentary
rocks.
 Gypsum is deposited in lake and
sea water.
 Hydrothermal anhydrite in veins
is commonly hydrated to gypsum
by groundwater in near surface
exposures.
 Often associated with the minerals
halite and sulfur.
http://en.wikipedia.org/wiki/Gypsum
USES OF GYPSUM
 Gypsum Board primarily used as a finish for walls and
ceilings; known in construction slang as Drywall
 Plaster ingredient.
 A component of Portland cement used to prevent flash setting
of concrete.
BRICK
 Masonry unit
 Does not infer any particular material
 About %90 of UK, bricks made from
some form of clay.
 %8 of UK bricks made of concrete
crushed rock aggregate and portland
http://www.urbanrevivals.com/images/brick/brick_all_web.jpg
cement are main constituents.
 %3 of UK of brick made from sand and lime,
sometimes with the addition of crushed flint.
REFERENCES
 WEB,http://www.fhwa.dot.gov/infrastructure/materialsgrp/cement.html
 WEB ,http://www.concrete.org/general/fE4-03.pdf
 WEB,http://architecture.arqhys.com/construction/properties-asphalt.html
 WEB,http://www.cement.org/basics/concretebasics_aggregate.asp
 Standard specification for portland cement (AASHTO M 85-89). 1986. AASHTO standard
specification for transportation materials. Part I, Specifications. 14th ed.
 Powers, T. C., L. E. Copeland, J. C. Hayes, and H. M. Mann. 1954. Permeability of portland
cement paste. ACl Journal Proceedings 51 (3):285-98.
 Whiting, D. 1988. Permeability of selected concretes. ACI special publication. Permeability of
concrete SP-108: 195-222.
 Tsuji, Y., and N. Miyake. 1988. Chemically prestressed precast concrete box culverts. Concrete
International: Design and Construction 10 (5):76-82 (May).
 Ramachandran, V. S., and R. F. Feldman. 1984. Cement science. In Concrete admixtures
handbook: Properties, science, and technology, ed. V. Ramachandran, 1-54. Park Ridge, N.J.:
Noyes Publications.
Thank you for your attention
 Simple question about our presentation.
What is the composition of concrete?
2. What is the purpose of curing?
3. What is the types of asphalt mostly used in construction?
4. What type of construction material is used for lining the
kilns?
1.
Wood
An Ancient building
Material
By
Engr. Dr. Attaullah Shah
SWEDISH COLLEGE OF ENGINEERING AND TECHNOLOGY
63
Wood
Wood and Timber
 Wood is a hard, fibrous tissue found in many plants. It has been used for
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centuries for both fuel and as a construction material for several types of
living areas such as houses, known as carpentry.
In the United Kingdom and Australia, timber is a term also used for
sawn wood products (that is, boards), whereas generally in the United
States and Canada, the product of timber cut into boards is referred to as
lumber.
Throughout history, the unique characteristics and comparative
abundance of wood have made it a natural material for homes and other
structures, furniture, tools, vehicles, and decorative objects.
Today, for the same reasons, wood is prized for a multitude of uses.
Types:
 Wood suitable for buildings: Timber
 Woof of fallen tree: Rough Timber
 Sawed and finished wood: Converted Timber /Lumber
 All wood is composed of cellulose, lignin, hemicelluloses, and minor
amounts (5% to 10%) of extraneous materials contained in a cellular
65
Types of Trees:
 Exogenous Trees/ Endogenous
 Exogenous Trees
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Grow in girth and material contained in the bark.
Most of the building wood
In the form of concentric rings called ‘”Annual rings”
Normally one rings represents one year growth
 Endogenous Trees:
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Grows inwards by adding every year a fresh layer of internally
The older formation are outside
Flexible and slender and not fit for buildings
 Deciduous/Evergreen Trees:
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Shed their leaves each winter –Building wood mostly
 Evergreen:
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Don’t shed leaves every winter
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X-section of tree:
Bark, Wood, Branches, and Cambium
 Cross section of white oak tree trunk:
 (A) outer bark (dry dead tissue):
 outer corky dead part (A), whose thickness varies
greatly with species and age of trees
 (B) inner bark (living tissue):
 which carries food from the leaves to
growing parts of the tree;
 (C) cambium:
 Outer ring between the sapwood and bark
 Lighter, weaker and vulnerable to decay.
 (D) sapwood:
 Transmits the sap from roots to branches
 (E) heartwood, (F) pith, and (G) wood rays.
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Sapwood and Heartwood:
 Sapwood is located between the cambium and
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heartwood
Sapwood contains both living and dead cells and
functions primarily in the storage of food;
In the outer layers near the cambium, sapwood
handles the transport of water or sap. The sapwood
may vary in thickness and number of growth rings.
Sapwood commonly ranges from 4 to 6 cm (1-1/2 to 2
in.) in radial thickness.
In certain species, the sapwood contains few growth
rings and usually does not exceed 1 cm (1/2 in.).
As a rule, the more vigorously growing trees have wider
sapwood. Many second-growth trees of merchantable
size consist mostly of sapwood.
68
.
 In general, heartwood consists of inactive cells that
function in either water conduction or food storage.
 The transition from sapwood to heartwood is
accompanied by an increase in extractive content.
 Frequently, these extractives darken the heartwood
and give species such as black walnut and cherry their
characteristic color
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Growth Rings
 In most species in temperate climates, the difference between
wood that is formed early in a growing season and that formed
later is sufficient to produce well-marked annual growth rings.
 The age of a tree at the stump or the age at any cross section of
the trunk may be determined by counting these rings.
 However, if the growth in diameter is interrupted, by drought
or defoliation by insects for example, more than one ring may
be formed in the same season.
 In such an event, the inner rings usually do not have sharply
defined boundaries and are termed false rings.
 Trees that have only very small crowns or that have accidentally
lost most of their foliage may form an incomplete growth layer,
some times called a discontinuous ring.
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Cross section of pine log showing growth rings. Light bands are early wood ,
dark bands latewood.
An annual (growth) ring is composed of an inner early wood zone and outer
latewood zone.
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Cutting and Sawing Lumber
Shrinkage, distortion, and warpage of lumber depends partially on
the way lumber is cut from a tree. Wood shrinks most in the
direction of the annual growth rings (tangentially); less across
these rings (radially); and very little parallel to the grain
(longitudinally).
Cutting and Sawing Lumber
Lumber can be cut from a log in two different ways: tangent to
the annual rings, called plain-sawed in hardwoods and flatgrained or slain-grained in softwoods.
Lumber cut radially to the annual rings is called quarter-sawed
in hardwoods, and edge-grained or vertical-grained in
softwoods.
Cutting and Sawing Lumber
Lumber is classified as quarter-sawed if the grain is 45 degrees to
90 degrees to the wide face and plain-sawed if the grain is 0
degrees to 45 degrees to the wide face.
Cutting and Sawing Lumber
Characteristics of plain-sawed lumber include:
1. Distinct grain pattern,
2. May twist, cup, or wear unevenly,
3. Tends to have a raised grain,
4. Shrinks and swells more in width, less in thickness,
5. Less waste in cutting, and therefore less expensive.
Cutting and Sawing Lumber
Characteristics of Quarter-sawed lumber include:
1. Relatively even grain pattern,
2. Wears evenly with less warpage,
3. Shrinks and swells more in thickness, less in width,
4. More waste in cutting and therefore more costly.
Wood Defects
 Variety of defects that affect the strength,
appearance, use, and grading of lumber. Defects
may be natural or caused by manufacturing.
 Wood can be damaged by insects, decayed by
fungus, and of course, destroyed by fire.
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Wood Defects
NATURAL DEFECTS:
Knot: branch embedded in a tree and cut
through manufacturing.
Shake: pitted area sometimes found in cedar
and cypress.
Pitched Pocket: opening between growth
rings and containing resin.
Check: lengthwise grain separation caused
by seasoning.
Split: lengthwise separation of wood
extending from one face to another.
Wane: lack of wood on the edge or corner.
Warp: shrinkage distortion of a plane
surface, includes---bow, crook, cup and
twist.
Seasoning of wood
 seasoning is process of drying out timber after
conversion. (Conversion felled trees are converted in
sawmills into thick plank sizes).
 Freshly cut wood contains considerable water, which amounts
to from one-third to more than one-half of the total weight.
 The drying of wood before it is processed into timber is called
seasoning, and is done for a number of reasons. Seasoned
wood is far more resistant to decay than fresh wood;
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 it is much lighter and therefore less expensive to ship; it has
much higher heating value, which is important if it is to be
used as fuel; and, most important, wood changes in shape
during drying, and this change in shape should be
completed before the wood is worked or used.
 Wood may be seasoned either by air-drying or kiln-drying.
Air-drying takes several months, whereas kiln-drying takes
a few days. In both cases, the wood must be carefully
stacked to prevent warping, and the rate of drying must be
carefully controlled.
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Wood Seasoning Methods
Air Seasoning – the natural method. Boards are stacked in the
open air with sticks (thin strips of wood) between them to allow
air to circulate. The stack is raised clear of the ground on piers
and has a roof to protect it from the weather.
The ends of the boards are painted, or have cleats (wood or metal
strips) nailed across them to prevent the end grain drying more
quickly than the rest of the board, as this causes splitting
(checking).
Advantages. It is cheap and needs little
skilled attention.
Disadvantages. It takes 3 to 6 years to dry.
The moisture content can only be reduced to
15 –18% by air seasoning.
 Kiln Seasoning – the artificial method.
Boards are stacked on trolleys with sticks
between them, and pushed into a kiln. The
kiln is sealed and seasoning proceeds in three
stages.
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Stage 1. Steam is injected at low temperature to
force free moisture out of the wood cells.
Stage 2. Steam is reduced and the temperature
is increased to dry the wood
Stage 3. Finally there is a flow of hot, almost
dry, air.
Advantages. It takes only a few days or weeks and kills insect eggs in the wood
(e.g. woodworm). It is possible to reduce moisture content to below 12%, making
the wood suitable for use in centrally heated and air-conditioned buildings
Disadvantages. Kilns are expensive to build and to run.
It needs a more attention and a lot of skill as incorrect drying will ruin he wood.
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 Water seasoning:
 Large logs are immersed in water for 15 days.
 Later dried in the open air.
 Suitable for wood containing more sap.
 Not suitable where strength is required like structural uses.
 Most of the fermentable matters removed and wood less
vulnerable to attacks of worms.
 Chemical seasoning or salt seasoning:
 Timber soaked in the solution of urea.
 Later dried in kiln.
 Electric seasoning:
 Quick but expensive.
 High frequency AC currents passed in the wood.
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Characteristics of good Timber
 Quality of timber depends on:
 Species used, the soil where tree is grown, time of felling and
methods of seasoning and treatment.
 Free of defects like knots, wanes, etc.
 Obtained from hearth of sound treed and sap removed.
 Uniform structure and color.
 Narrow annual rings.
 Heavier in weight
 Firm adhesion of fibers.
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Causes of wood decay and preservation
 Wood is naturally a very durable substance. If not attacked by living
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organisms, it will last for hundreds or even thousands of years.
Samples of wood used by the ancient Romans have been found virtually in
their original condition when a combination of circumstances protected
them against attack.
The most important of the organisms attacking wood are the fungi that
cause so-called dry rot, which actually occurs only when the wood is damp.
The sapwood of all trees is susceptible to this type of decay, but the
heartwood of a few species is naturally resistant to these fungi. Walnut,
redwood, cedar, mahogany, and teak are among the well-known woods that
are extremely durable
Other woods are resistant to various types of attack. Greenheart and teak are
particularly resistant to the attack of marine borers, and so are often used for
underwater construction for wharves.
A number of woods are comparatively resistant to termites, including
redwood, black walnut, mahogany, and several types of cedar.
In most of these cases, the woods are aromatic, and the resistance is
probably due to the resins and similar chemicals they contain.
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 Wood may be preserved by protecting it chemically against
deterioration. The most important method of treatment has long been
impregnation with creosote or zinc chloride.
 This method is still one of the best, although a number of newer
chemicals, notably several containing copper compounds, have been
introduced for the same purpose. Wood can be protected against
weathering by suitable surface coatings, applied by brushing, spraying,
or dipping. Surface applications yield little penetration, however, and
therefore do not prevent deterioration under attack by insects, fungi, or
borers.
 By applying a finish to wood we not only protect it but tend to improve
its appearance. A highly polished dining table or floor is not only safe
from attack by organisms and chemicals they become more attractive
or aesthetically pleasing. New paints and coatings are constantly being
developed to improve and enhance the appearance and properties of
both natural and processed wood
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 Commonly used wood preservation techniques:
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A good preservative must be:
 Cheap - Easy to use and handle - Non injurious to the tissues of
trees- Should preserve permanently and must not wash.
 Should not affect the color of the wood.
 Methods of Preservation
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Brush treatment and painting
 2-4 coats of oil, paint or creosote
Charring of timber:
 Charring the outer fibers of timber by fire
 Envelop of charcoal is devoid of food and restricts fungi.
 Reduces the strength as burns the outer fibers.
Dipping:
 Dipped in preservative and soaked for few minutes.
 Used for lower ends of poles and wooden piles.
Creosoting;
 Moisture extracted and the vacuum filled with creosote
 Creosote is by-product coal tar produced in manufacture of coal gas
Engineered Wood Products
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OSB
LVL
Plywood
Particle Board
Glulam
MDF
I-Beams
Trusses
Particle Board
manufactured from wood particles, such as wood chips, sawmill
shavings, or even saw dust. Made with larger pieces of wood
than used to make MDF
Chipboard or Particleboard
Most chipboard is of graded density, having smaller chips packed
tightly together on the outside to give a smoother and stronger
face. Chipboard is made by gluing wooden chips together under heat
and pressure.
It is suitable only for interior use. Veneered and melamine-faced
chipboard is widely used for worktops, shelves and furniture
making.
Usual sheet size is 2240 x 1220mm. Common thicknesses are
12mm and 18mm.
Blockboard and Laminboard
These are made by sandwiching strips of
softwood between two plies. The strips
are narrower in laminboard than in
blockboard.
They are usually made in interior grade only. The grain of the face
plies runs at right angles to the core strips. The core strips are
arranged with the heartside alternately on top and underneath (as
when edge jointing boards) to avoid warping.
Both block and laminboard can be faced with veneers of
decorative hardwood.
It is usually cheaper to make blockboard than to make multiply
over 12 mm thick.
Usual sheet size is 2440 x 1220mm. Common thickness is 18mm.
Hardboard
Hardboard is made by mixing wood fibres with water and synthetic
resin glue, hot-pressing it into sheets and leaving it to dry.
It is not very strong and is usually fixed onto a wooden frame.
Standard grade is for interior use. Tempered grade is impregnated
with oil for exterior use and for bending to make curved shapes.
Can be melamine-faced or ready painted.
Medium Density Fibreboard (MDF)
A fairly new material (1979) but extensively used that is like a very
smooth chipboard.
Fibreboard is made from a pulp of wood or other vegetable fibres
which is dried under heat and pressure.
For adhesion it relies principally on the natural resin contained in
the pulp.
It is used for model-making, light structural items such as speaker
cabinets and extensively for furniture – wardrobes kitchen units etc.
Usual sheet size is 2240 x 1220mm but may be supplied in half or
quarter sheets. MDF is available in a large range off thickness
from 5mm to over 50mm.
Oriented Strand Board (OSB)
Oriented Strand Board (OSB)
Laminate Strand Lumber (LSL)
Made up of strands of lumber instead of veneers
Laminated Veneer Lumber (LVL)
LVL is made by gluing sheets of veneer together. Unlike plywood, here all veneer layers
are going in the same direction. Wide panels are manufactured to the thickness of the
desired lumber. The panels are ripped into lumber of nominal width.
Masonite
Type of hardboard invented by William H. Mason. It is formed using the
Mason method, using wooden chips and blasting them into long fibers with
steam and then forming them into boards. The boards are then pressed and
heated to form the finished boards. No glue or other material is added.
Plywood
made from thin sheets of wood veneer, called plies or veneers,
layered in opposite directions
WOOD MATERIAL THEORY
Plywood
This is made from layers or plies of wood glued together so that the
grain of each ply is at right angles to the next. There is always an
odd number of plies so that the grain runs the same way on both
outside pieces and hence stresses are balanced.
Traditional 5- ply
plywood
Direction of layers at 90
degrees to each other
WOOD MATERIAL THEORY
Plywood can be faced with a veneer of decorative
hardwood to improve its appearance, or with melamine to
give a harder wearing surface.
Plywood is graded for interior or exterior
use depending on the water resistance of the
glue used, and this is shown by code letters
on each sheet.
WBP – Weather and boil proof.
BR – Boil resistant
MR – Moisture resistant
Int. – Interior use only
Plywood is also graded by the smoothness of the surface and
number of defects in it.
Plywood can be nailed near the edge without splitting. Thin
plywood is flexible and can be formed into curved shapes.
Usual sheet sizes are 2440 x 1220mm and 1525 x 1525mm.
Common thicknesses are 4, 6, 9 and 12 mm.
Wood I-Beams
Veneer lumber is used for the flanges and plywood or OSB is
used for the web to resist shear.
Glued Laminated Lumber (Glulam)
These beams are made by gluing many boards together to form a structural member
bigger than the trees from which the board were sawn. Since the load is carried by the
material in the top and bottom faces and the middle only has to resist shear, high
quality lumber is used in the top and bottom while medium grade lumber is used in the
center. (gluelam or glulam) Joints between boards are typically scarf of finger joints.
Wood Trusses
Important Wood types
 Deodar ( Cedrus Deodara)
 Kail ( Biar) or Blue Pine ( Pinus excelsa)
 Chir ( Pine) ( Pinus Longifolia)
 Bamboo or Bans ( Bambusa).
 Jaman
 Mango
 Neem
 Olive
 Phulai
 Shishum ( Tali)
 Teak or Sagwan.
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Group Assignment
G-1: Write the names of most commonly used two softwoods and
two hardwoods. Explain their properties and uses in Civil
Engineering.
G-2: Explain various methods for seasoning of wood.
G-3: Types and uses of Engineered Wood
G-4: Structural uses of Wood in Civil Engineering
G-5: Characteristics of Good Quality Wood.
G-6: Compare Plywood and Laminated Veneered Lumber ( LVL)
G-7: Common Types of Defects in Wood and their remedies
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