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Title: HARDENED CONCRETE
Description: Now this here guys is the real deal.all that you want to know about HARDENED concrete is in here you don't have to peruse through websites to get the information just did it for you.
Description: Now this here guys is the real deal.all that you want to know about HARDENED concrete is in here you don't have to peruse through websites to get the information just did it for you.
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Hardened Concrete
vIt is important for the engineer to understand the basic
properties of hardened Portland cement concrete and to
be able to evaluate these properties
...
Strength
Strength = ability to resist stress without failure
v
The most important property that is often required, simply
because Concrete is used for compressive loads
...
3 to 5
...
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Ø The strength of a concrete specimen prepared,
cured and tested under specified conditions at a
given age depends on:
ü
Amount of Cement
ü
Water-Cement Ratio
ü
Other influencing
factors:
§ Admixture(s)
§ Aggregate
Selection &
Gradation
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Typical sizes of test specimen
150 x 150mm cubes – British standard
Other sizes:
Cylinder:
Cubes:
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100 × 200 or 150 × 300 mm
100 × 100 × 100 mm3
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Typical Failure Modes for Test Cubes: (a) Non
-explosive; (b) explosive
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Tensile strength
Ø Tensile Strength can be obtained either by direct
methods or indirect methods
...
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SPLIT TENSILE STRENGTH
vThe split-tension test (ASTM C496) measures the
tensile strength of concrete
vConcrete cylinder of 150mm by 300mm is subjected
to a compressive load at constant rate along a
vertical diameter until failure
v
Failure is due to tension developed in the
transverse direction
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SPLIT TENSILE STRENGTH CONT…
Due to applied compression load a fairly uniform
tensile stress is induced over nearly 2/3 of the
diameter of the cylinder perpendicular to the
direction of load application
...
• The test is simple to perform and gives uniform
results than other tension tests
...
The results
obtained are useful
because concrete
is subjected to
flexural loads more
often than it is
subjected to tensile
loads
...
vThe length of beams should be at least three times
the depth of the beam plus 50 mm
...
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2
...
However, specially for
cylindrical specimens
with h/D=2, it can be
assumed as linear
upto 40-50% of σult
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Modulus of Elasticity
As per ASTM
S2 = stress at 40% of ultimate load with a strain
of ε2
S1 = stress at ε1 equal to 0
...
5 [f’c]0
...
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Calculation example
For normal-weight concrete, the relationship used in
the United States for designing concrete structures is
defined by the ACI Building Code as
A normal-weight concrete has an average
compressive strength of 30 MPa
...
Durability of Concrete
vDurability of concrete performs satisfactory under
anticipated exposure conditions towards life time of
the structure
vConcrete is very durable, but concrete structures
have shown poor durability and strength loss within
few year of their service
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Durability of concrete is based on:
üResistant to freezing and thawing
üAppearance of cracks
Resistance to freezing and thawing can be minimized:
ØControl Air entrainment
Ø
Control w/c
Cracking
ü
Path of harmful materials to get into concrete
§ Sulphate causes severe expansion and deterioration
§ Chloride initiate corrosion
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Factors affecting durability of concrete includes:
vPermeability
ü
Permeability is an important factor that largely affects the
durability of hardened concrete
...
ü
Water that permeates into reinforced concrete causes
corrosion of steel reinforcements
...
:
vThe permeability of concrete is due to presence of air
voids
vThe air voids that affect permeability of hardened
concrete are obtained from two main sources: incomplete
consolidation of fresh concrete and voids resulting from
evaporation of mixing water that is not used for hydration
of cement
vTherefore, increasing the water–cement ratio in fresh
concrete has a severe effect on permeability
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Factors affecting durability of concrete cont
...
vAge reduces the permeability, since hydration products
fill the spaces between cement grains
...
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Factors affecting durability of concrete cont
...
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4
...
vCreep of concrete is a long-term process, and it takes place over
many years
...
vThe effect of creep varies with the type of structure
...
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vShrinkage is a negative volume change due to
drying and hardening causes water to evaporate
from cement paste
vShrinkage:
ü Increases with decreasing humidity,
with
ü Increases with increasing cement-to-aggregate
with
ratio: Cement paste shrinks, aggregate does not
shrink
vIncreases with increasing water-to-cement ratio:
with
More water, less aggregate,
l water evaporates, paste shrinks, aggregate
does not shrink
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vIncreases with increasing fineness of cement,
with
l Finer
cement absorbs more water, water
evaporates, more shrinkage
...
shrinkage
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vThe rate of creep decreases with time and the creep strains at
five years are taken as terminal values
...
Ø
Depth is inversely related to the strength
...
Ø
Rebound hammer tests only the surface while
penetration resistance test make measurements into
the depth of the sample
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Ultrasonic Pulse Velocity Test (ASTM C597)
Ø
Measures the velocity of an ultrasonic wave passing through the
concrete
Ø
The length between transducers/the travel time = average
velocity of wave propagation
Ø
It is used to detect discontinuities, cracks and internal
deterioration in the structure of concrete
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Title: HARDENED CONCRETE
Description: Now this here guys is the real deal.all that you want to know about HARDENED concrete is in here you don't have to peruse through websites to get the information just did it for you.
Description: Now this here guys is the real deal.all that you want to know about HARDENED concrete is in here you don't have to peruse through websites to get the information just did it for you.