ppt

1. UNIT -5- (8L+0T+0P)
Properties of Hardened Concrete:
Mechanical properties of concrete-Compressive strength, Split tensile strength, Flexural strength,
modulus of elasticity and bond strength tests, Tests on NDT.
Durability: Definition, significance, short term and long-term durability. Sulphate attack,
Chloride attack, carbonation of concrete, freezing and thawing, alkali aggregate reaction, alkali
silica reaction, effect of corrosion of steel on concrete.
Properties affecting the strength and durability of concrete
Shrinkage – Autogenous shrinkage and drying shrinkage, Factors affecting shrinkage, Factors
contributing to cracks in concrete

2. TEST FOR HARDEN PROPERTIES
OF CONCRETE
• Many destructive and non destructive tests are conducted
on hardened concrete to measure their properties such as
strength, permeability and durability;
Destructive testing
(Specimen is broken down)
Non-Destructive testing
(Specimen is not broken
down)
1. Compressive strength test
2. Flexural Strength test
3. Splitting tensile test
4. Modulus of elasticity
5. Pull out test etc.
1. Ultrasonic pulse velocity test
2. Rebound hammer test
3. Electrical resistivity test
4. Other corrosion studies
2

3. 3
TEST FOR HARDEN PROPERTIES
OF CONCRETE
Before starting these tests some of the points
should be considered,
• Concrete mix should be uniform and well compacted
• Curing should be proper
• At least three specimens are needed for a single test
and average value of these three specimens is taken.
• Each specimen test result should not exceed 5% of the
result of other specimens, if exceeded it indicates the
poor mix of concrete.

4. 1. Compressive strength of
concrete
P
Top plate of
Universal Testing
machine
Cylindrical
Specimen
Bottom plate of
Universal Testing
machine
4

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1. Compressive strength of
concrete
Testing procedure
• These cured specimens are taken from the curing tank
and excess water is removed from the surface.
• The cleaned specimens are tested by compression
testing machine after 7 days curing or 28 days curing
as required.
• Load should be applied gradually till the Specimens
fails.
• Load at the failure is noted and the compressive
strength of concrete can be calculated by the ratio of
failure load to surface area of the specimen
i.e f= P/A

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1. Compressive strength of
concrete
As per Indian standard code, the compressive
strength improvement percentages is
presented in the table
Curing period in days
Strength improvement in
percentage
1 16
3 40
7 65
14 90
28 99

9. 2. Flexural strength test
L/3 L/3 L/3 L/2 L/2
L
(b)
L
(a)
P
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P P

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2. Flexural strength test
Test procedure:
• Prepare the test specimen by filling the concrete into the
mould in 3 layers of approximately equal thickness. Tamp
each layer 25 times using the tamping bar.
• The specimen is placed to the machine as shown in above
figure.
• Hence the load is applied gradually to the specimen and
failure of the specimen is carefully noted.
• After getting of failure loading, the flexural strength can be
calculated by using following expression,
fb = PL/bd2
Where, P-load, L-Length of the specimen, B and d- breadth and depth of
specimen

12. TENSILE STRENGTH
• Tensile strength is one of the basic and important
properties of concrete. A knowledge of its value is
•
required for the design of concrete structural elements.
Its value is also used in the design of prestressed concrete
structures, liquid retaining structures, roadways and
runway slabs.
• Direct tensile strength of concrete is difficult to
determine; recourse is often taken to the determination
of flexural strength or the splitting tensile strength and
computing the direct tensile.

13. What is split tensile strength test?
A method of determining the tensile strength of
concrete using a cylinder which splits across the
vertical diameter. It is an indirect method of testing
tensile strength of concrete.
Why we are going for split
tensile test?
• In direct tensile strength test it is impossible to apply true
axial load. There will be always some eccentricity present.
• Another problem is that stresses induced due to grips. Due to
grips there is a tendency for specimen to break at its ends.

14. Computations: Calculate the splitting tensile
strength of the specimen as follows:
T = 2P
πLd
Where:
T : splitting tensile strength, kPa
P : maximum applied load indicated by testing
machine, kN
L : Length, m
d : diameter, m

15. Bond Strength

16. Bond strength is defined as the strength with which a chemical bond holds two atoms together in
chemistry. This is usually expressed in terms of the amount of energy required to break the bond
in kilocalories per mole.
Bond Strength

17. Factors Affecting Bond Strength
The amount of energy necessary to break one mole of a specific type of bond and separate it into gaseous atoms is
known as bond energy. The bond energy is directly related to the strength of a chemical bond.
The following are the factors that affect the bond strength.
• The bond length increases as the atom’s size increases, and the bond dissociation energy decreases, resulting
in a decrease in bond strength.
• The bond dissociation energy of a bond between two identical atoms increases as the bond multiplicity
increases.
• The larger the number of lone pairs of electrons on linked atoms, the greater the repulsion between them, and
thus the lower the bond dissociation energy.
• As the hybrid orbitals’ orbital contribution grows, the bond energy increases. As a result, bond energy drops in
the order sp sp2 sp3.
• The higher the electronegativity difference, the higher the bond polarity and thus the bond strength.

18. Determination of Modulus
of elasticity
Top layer of UTM
machine
Compressometer
Dial gauge
Specimen (150 mm dia.
with 300 mm height)
Bottom layer of
UTM machine
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19. Modulus of elasticity of concrete(Ec) is defined as the ratio of the applied stress to the
corresponding strain. Not only does it demonstrate the ability of concrete to withstand
deformation due to applied stress but also its stiffness. In other words, it reflects the ability
of concrete to deflect elastically. Modulus of elasticity of concrete is sensitive to aggregate
and mixture proportions of concrete.

20. Determination of Modulus of elasticity (cont)
Strain

21. Determination of modulus of elasticity of Concrete
• Testing of cube or cylinder in uni-axial compression test.
• Measure load and the corresponding deformation as the load is increased.
Draw the stress strain curve.
• Strain =Dial gauge reading/gauge length = dl/L
• Stress = Load/Cross sectional area= P/A
• Use Compressometer and Extensometer to measure deformations. Draw
stress strain diagram and determine the required modulus.
• Deflection: E can be determined from testing of beam also.

22. Determination of Modulus of Elasticity

23. • The test uses a 150 X 300 mm cylindrical specimen, which is loaded in
compression. A compress meter is used to measure the longitudinal
strains, and an extensometer is used to measure the transverse strains on
the specimen.
• The chord modulus (E) is calculated as:
□ where S2 = stress corresponding to 40% of ultimate strength
□ S1 = stress corresponding to a strain of 50 X 10-6
□ Ε2 = longitudinal strain produced by stress S2
Determination of Modulus of Elasticity

32. Definition :
The durability of cement concrete can be defined as its ability to resist
weathering action, chemical attack, abrasion or any other process of
deterioration. A durable concrete should maintain its original form and
serviceability when exposed to adverse environment.

33. Factors affecting the durability of concrete
The strength of the concrete depends on many factors, as described below.
• Quality & Shape of Coarse Aggregates
• Quality of Fine Aggregate
• Quantity of Cement
• Mix Ratio
• Water Cement Ratio
• Cover Provision
• Compaction of Concrete
• Workmanship
• Curing Period
• Moisture content
• Sulphate Attack
• Chloride attack
• Environmental Conditions

34. Quality & Shape of Coarse Aggregates
The quality of coarse aggregates is significant for the durability of concrete. The coarse aggregate, which
occupies 70-80% of the concrete volume, is responsible for its compressive strength.
• The irregular shape of aggregates makes more voids in concrete.
• The angular aggregates make bonding with each other, and it helps develop the strength of the concrete.
Quality of Fine Aggregate
The river sand is used as filler material in concrete. It should be free from silt & other marine impurities.
The silt content test for sand has to be performed to measure the silt particles in sand. The allowable silt in
the sand in the ranges between 6 to 8%.

35. Quantity of Cement
The durability of concrete will be affected by the shrinkage of concrete.Ordinary Portland Cement
If the cement content is exceeded, it leads to shrinkage happening in concrete.
The lower cement content decreases the bondage between the concrete materials, reducing concrete
strength.
Mix Ratio
The proper recommended mix ratio should be used for any construction work. Improper mix ratio
directly affects the compressive strength of the structure. Eventually, it led to structural failure.
Water cement Ratio Concrete Mix
A high amount of water increases the porosity in concrete then the water molecules easily penetrate the
concrete and rust the steel bar.
In the case of low water content in concrete, it affects the workability of concrete. The recommended
water-cement is 0.45 to 0.65 as per IS standards.