Chapter-1-Introduction.pptx

Chapter-1 (4 hrs)
Introduction
1.1 Scope of construction materials
1.2 Selection criteria of construction materials
1.3 Classification of construction materials
1.4 Properties of construction materials
1.5 Griffith’s theory
1.6 Hardness and toughness tests of construction
materials
Prepared by: Ramesh Bala; Khwopa College of
Engineering 1

Scope of the Subject
Civil Engineering Sector
 Hydropower -> construction of
Power house, dam reservoir and
other structures.
 Road Construction -> Road
Protection work, Retaining Wall,
Pavement Work etc
 Building Construction ->
Foundation work, Superstructure
work, Finishing work etc
 Water Supply -> construction of
headwork , canal, dam etc
 Sanitary -> Drainage system,
sludge tank construction etc
Engineering 2

1.2 Selection Criteria of Construction
Material
Material selection criteria depends upon:
 Locally availability of natural resources
 Availability of skilled Manpower
 Availability of material in nearest market
 Technology Used
 Budget availability
 Economic Benefit
Engineering 3

1.3 Types of construction materials:
A) According to chemical compositions
1) Organic materials:
◦ Organic materials contains basically carbon as
key material
◦ E.g.: timber, plastic, bitumen, petroleum etc.
2) Inorganic materials:
◦ Inorganic materials basically contain silica,
calcareous materials containing calcium
compounds & argillaceous materials like clay.
Prepared by: Ramesh Bala; Khwopa
College of Engineering 4

B) According to uses:
1) Structural material
 Stone, brick, steel etc.
2) Aesthetic material
 Tiles, marbles, paints etc.
C) According to existence:
1) Natural material
 Stone, sand, clay, wood etc.
2) Artificial material
 Cement, plastic, brick etc.

D. According to metallurgy
Metal
 Ferrous metal and its alloys e.g. Cast Iron,
Wrought Iron and steel similarly silicon steel,
spring steel etc
 Non Ferrous metals and their alloys e.g.
copper, aluminium, zinc etc similarly, brass ,
bronze etc
Non- Metal
 e.g. Building Stones, Cement, Rubber,
Plastics, Paint and Varnishes, asbestos ,etc
Engineering 6

1.4 Properties of Construction Materials
 Physical Properties
 Mechanical properties
 Thermal Properties
 Electrical Properties
 Magnetic Properties
 Chemical Properties
Engineering 7

Physical Properties
1. Specific gravity:
 It is the ratio of density at material to the density of
water at standard condition.
2. Density:
 It is the ratio of mass of the material to the total volume
of the materials.
 Density = M/V Unit kg/m3
3. Porosity:
 It is the ratio of volume of voids in the material to the
total volume of the materials.
Engineering 8

4. Permeability:
 It is the property where by the material allows
water to pass through its pore.
5. Water absorption:
 It is the ability of material to absorb & retain
water.
6. Fire resistance:
 It is the property of material to resist fire
7. Durability:
 It is the resistance of material to disintegrate by
natural agencies like humidity variation,
chemical attack, action of atmosphere gases
etc. Prepared by: Ramesh Bala; Khwopa

Mechanical properties
Mechanical properties are important to determine the load resisting
capacity, durability etc. These are:
1. Strength:
 property of material to resist the applied load without failure.
 Common types of strength properties found in construction
material are:
a. Tensile Strength:
 It is maximum stress that a material can withstand under a
tensile load without failure is known as strength.
b. Compressive strength:
 It is maximum stress that a material can withstand under a
compressive load without failure is known as compressive
strength.
c. Shear Strength:
 It is the maximum stress that the material can withstand
under shear force without failure is known as shear strength.

Stress and Strain
• When a body is
loaded, the restoring
force per unit area,
comes into play inside
the body, it is called
stress. Its unit is
N/mm2 or KN/m2.
• Types:
1. Tensile stress
2. Compressive stress:
3. Shear stress:
• change in dimension
to original dimension
when a body is
subjected to external
force
• Types:
1. Tensile strain
2. Compressive strain
3. Shear strain

Tension, compression, shear, and torsion

2. Elasticity
property of material by which material tends to
regain its shape after the removal of applied
load.
Elasticity of material is defined upto limit called
elastic limit. After crossing this limit material
become plastic.
A material is said to be perfectly elastic if the
whole of the stress produced by a load
disappears completely on the removal of
the load.
The modulus of elasticity of young’s
modulus (E) is the proportionality constant
between stress and strain for elastic materials.
Prepared by: Ramesh Bala; Khwopa College of Engineering 13

 Poisson’s ratio – The ratio of lateral
or transverse strain to the longitudinal
strain.
Poisson’s ratio for most materials ranges
from 0.25 to 0.35.
Cork ⇒ ν ≈ 0.0
Steel ⇒ ν = 0.27 – 0.30
Aluminum ⇒ ν = 0.23
Rubber ⇒ ν ≈0.5 (limiting value for
Poisson’s ratio)

3. Plasticity -> property that enables
the formation of permanent
deformation in a material. Gold and
lead are highly plastic material.

4. Ductility -> ability of metal to
withstand elongation or bending. Due
to this property, wires are made by
drawing out through a hole.
5. Malleability -> property by virtue of
which a material may be hammered or
rolled into thin sheets without rupture.
Such properties increase with increase in
temperature.

6. Toughness (or tenacity)
 ability of material to
absorb energy due to
straining action
undergoing the plastic
deformation
 Due to molecular
attraction of metal the
power resist the metal
tearing apart, strength
with which the material
rupture.
 Area under stress strain
curve indicate the
toughness.
 It is express as energy
absorbed (Nm)per unit
volume of material

7. Brittleness -> lack of ductility thus break
easily when subjected to shocks.
8. Hardness -> resistance of material to
penetration. It resist scratch or being worn
out by friction with another body.
9. Fatigue -> development of facture
when material subjected to fluctuating
or repeating load. Such failure starts at
the point of highest stress.

10. Creep -> Slow plastic deformation of
metals under constant stress or under prolong
loading usually at high temperature.
11. Impact strength:
 It is the property of material to the resist certain
sudden shock or impact over the material.
12. Abrasive Resistance
 property to resist the wearing of the surface of
the material due to the friction between one
another.

13. Resilience: is the capacity of a material
to absorb energy when it is deformed
elastically and then, upon unloading, to
have this energy recovered.

Chemical Properties
- describes the combining tendencies,
corrosion characteristics, reactivities,
solubilities, etc. of substances.
- Some chemical properties are:
 Corrosion resistance
◦ Corrosion is a gradual chemical or electro
chemical attack on a metal by its
surroundings so that the metal is
converted into an oxide, salt or some
other compound.
Engineering 21

 Oil & petrol resistance:
◦ ability of material to withstand attack by
liquid, fuels etc.
◦ Oil & petrol resistant must be taken
choosing floor covering for garage,
industrial building, service station etc.
 Acid resistant & alkali resistant:
◦ ability of material to withstand attack by
acid & alkali respectively.

Thermal properties of material
 Important in the
structure where there is
frequent change in
temperature.
1. Specific heat capacity:
 It is defined as the
amount of heat required
to raise the temperature
of unit mass of material
by 1⁰C.

2. Thermal conductivity (K):
 amount of heat transmitted in unit time
through unit area over unit length
perpendicular to the direction of heat
flow when the temperature gradient
across the heat considering unit is
1⁰C.

Electrical Properties
- It indicates the ability of material to permit or
resist the flow of electricity.
- Following are the electrical properties of
material:
 Resistivity - Electrical property of material
that resists the flow of electricity through it.
Resistivity, ρ =
R.A
l
Where, R = resistance of the conductor
A = cross section area of the
conductor
l = length of the conductor

 Conductivity - reciprocal of resistivity. i.e.
material provides an easy path for the flow of
electricity through it.
σ =
1
ρ
=
l
R.A
 Temperature coefficient of resistance -
indicate the variation of resistivity with
temperature.
αT=
ρ−ρo
ρo
1
T−To
Where,
Ρ = resistivity at temp. T
ρo= resistivity at temp. To
T and To are degrees kelvin Prepared by: Ramesh Bala; Khwopa

Electrical Properties cont. ..
 Dielectric strength - insulating capacity
of a material against high voltages. A
dielectric is an insulation.
 Thermoelectricity
– production of small
voltage in the junction between two
dissimilar metals when they are joined
together.
Engineering 28

Magnetic Properties
 Such properties of material create a
magnetic field in the surrounding.
- Magnetic properties arise from the
spin of electrons and orbital motion of
electrons around the atomic nuclei.
- Study of magnetic properties is
necessary as it helps to know the
structure and behavior of the matter.
Engineering 29

Magnetic Properties of
Materials
 Ferromagnetic: material with a
permanent magnetic dipole
 Paramagnetic: material attracted by
a magnetic field
 Diamagnetic: material repulsed by a
magnetic field
 Non-magnetic: material insensitive
to a magnetic field

 Define the term ductility and
resilience. Determine the young’s
modulus and Poisson’s ratio of
metallic bar of length 60cm, breadth
6cm, when subjected to an axial
tensile load of 500KN. The increase in
length as 0.09cm and decrease in
depth is 0.005cm

Griffith theory for brittle
fracture:
 Fracture is a separation of a body
caused either by physical or chemical
forces into two or more parts resulting
in the creation of new surface.
 When the fracture of material occurs
without or with less plastic deformation
the fracture phenomenon is known as
brittle fracture.

 The fracture of brittle material was
studied by A. A. Griffith in 1920.
 He suggested that, “in any brittle non metallic
substances such as glass, minute crack or
fissures particularly occurring at the surface
acts as stress raiser by concentrating
stresses at their tips.”
 It means energy required for fracture of
brittle material is not uniformly distributed
over the volume of materials. But their
region of energy concentrated is
produced by minute faults & cracks in the
materials. Prepared by: Ramesh Bala; Khwopa

Griffith theory of brittle fracture:
Crack propagation criterion:
 Consider a through thickness crack
of length 2a, subjected to a uniform
tensile stress σ, at infinity.
 Crack propagation occurs when the
released elastic strain energy is at
least equal to the energy required
to generate new crack surface.

The stress required to create the new crack
surface is given as follows :
where,
σ = critical stress
E = Young’s modulus of elasticity
γs= Surface energy per unit area
a = half of length of an internal cracks
Note:
Fracture stress depends upon:
• Crack size
• Properties of material

Hardness & Toughness test of
Construction materials
Hardness tests
 One of the most simple & useful property
of metal is hardness.
 Hardness is used to find out many
qualities of a metal.
 indicate resistance to abrasion,
scratching, cutting or shaping.
 It may denote strength, stiffness,
brittleness etc.
 The hardness of the material implies the
resistance to deform or indentation.

Three types of hardness
tests:
1) Scratch hardness test
 determines scratching & abrasion
quality of a metal when scratched
by a standard substance.
 The standard substances are
either minerals or files.
 Some minerals have been given
hardness numbers from 1 to 10 on
the Mohr scale.
 The softest mineral on this scale is
talc.
 Diamond has the maximum
hardness of ten (10).
 determined by trial method like
which minerals scratch a smooth
surface of substance & which
mineral can be scratched by the
substance.
Mohr scale

 Another method is filling. The mineral
to be tested is rubbed against a
standard file or vice-versa & it is noted
whether a visible cut is produced or
not on the metal surface.
 The visible cut on the metal surface is
produced if the hardness is lower than
that of the file.

2) Indentation hardness test or penetration
test
 based on the principle of forcing a hard
material called an indenter against a flat
surface of the metal whose hardness is to be
measured under a fixed load depending upon
its hardness.
 The metal resists deformation & finally an
impression is made by the indenter on the
surface of the metal.
 The diameter or depth of the impression
determines the hardness of the metal & after
the measurement it could be converted into a
relative quantitative value.Prepared by: Ramesh Bala; Khwopa

 Some of the indentation hardness
tests are:
◦ Brinell hardness test
◦ Rockwell hardness test
◦ Vickers hardness test

i) Brinell hardness test
 The test consist in
forcing a steel ball of
diameter, D under a
load P into the test
piece & measuring
the mean diameter
of the indentation
left in the surface
under test after
removal of the load.

ii) Rockwell hardness test
 In this method, Rockwell
test machine measures the
depth of impression, the
measurement is read on
the dial of the micrometer
which is connected to the
indenter,
 The indenter in Rockwell
hardness testing machine
is either a steel ball, hard
steel ball or a carefully
ground diamond cone.
 Ball size varies from 1.5
mm to 3 mm diameter

Method:
 A completely flat specimen is supported by
the Anvil of the machine which is raised up
by a jack-screw until the specimen comes
in contact with the indenter.
 A minor load is then applied by raising
Anvil.
 The final load is then applied by releasing a
system of levers which forces the indenter
down onto the surface of the specimen.
 Before the reading of dial-gauge, the laser
is taken, the major load is removed leaving
the indenter in the new position but only
under the minor load of 10 kg.

iii) Vickers hardness test
 This test is similar to Brinell
hardness test.
 In this test indenter is a diamond
pyramid having four side.
 The angle between opposite side
is 136⁰. The indenter size is
square.
 The load is automatically applied &
released after the correct time.
 The specimen is removed from the
indenter & diagonal of the
impression is measured using
microscope & eliminating lamp.

3) Rebound hardness test
 In this test, the specimen at which hardness
is determined by dropping on a small
diamond pointed hammer, on the surface
& observing the height of rebound.
 A steel cylinder hammer is dropped from a
height of 25 cm through a glass tube on the
surface to be tested.
 The height of the rebound is used as a
measure of hardness of surface.
 The surface to be tested should be smooth,
free from oil and tube should be truly vertical.

Impact Test:
 When materials are subjected to a
sudden stress or shock, the behavior
of the material will not be as that in the
case of hardness test.
 Impact test is performed for very rapid
stresses & the impact load is applied
by swinging pendulum which collides
with the specimen.

Charpy
test:
A standard specimen of
55 mm long 10 mm
square section with U-
Notched facing
downward is supported
at each end.
i. Striking energy of
the testing machine
should 30 kg force-
meter & the
difference between
the supports is 40
mm.
ii. Notched in 5 mm
deep rounded off at
the base with a
iii. The test piece is
stroked by hammer in a
plane of symmetry of
notched & on the side
opposite to the notched.
Then impact strength of
the material is noted
from dial gauge.

 iv. The impact strength is the energy
absorbed per unit volume during the
fracture of the materials.

Izod test:
 The test consist
breaking of the
specimen by one
blow from a
swinging hammer.
 The specimen is
placed vertically
with bottom of the
Notched. In the
same plane, the
blow is stroked.

for your kind attention

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