Concrete strength Today i am writing about Strength of Concrete / Concrete Strength as you know that last time i published a post about the Testing Concrete or test of concrete some of my website viewers comment about to make a guide about Strength of Concrete / Concrete Strength . So i make a simple and easy post about in which i explain you all about How To Find Strength of Concrete/Concrete Strength .
How To Find Strength of Concrete/Concrete Strength
STRENGTH OF CONCRETE.
There are many factors affecting the concrete strength .The most important of these is quantity of element in the concrete. The more the quantity of cement in the concrete the more will be its strength. Other factors are water-cement ratio, curing, compaction etc .By setting out these factors at adequate standard, the strength of concrete is calculated the different ratios also considered the standard strength of the concrete .The strength of concrete increases with the passage of time .Under normal circumstance the strength of concrete becomes 70 % after 7 days of placing the concrete. This becomes more than 90% after 28 days. For the design purposes generally 28 days strength of concrete is considered .This is recorded below.
Permissible Strength in Concrete.
How To Find Strength of Concrete/Concrete Strength
STRENGTH OF CONCRETE.
There are many factors affecting the concrete strength .The most important of these is quantity of element in the concrete. The more the quantity of cement in the concrete the more will be its strength. Other factors are water-cement ratio, curing, compaction etc .By setting out these factors at adequate standard, the strength of concrete is calculated the different ratios also considered the standard strength of the concrete .The strength of concrete increases with the passage of time .Under normal circumstance the strength of concrete becomes 70 % after 7 days of placing the concrete. This becomes more than 90% after 28 days. For the design purposes generally 28 days strength of concrete is considered .This is recorded below.
Permissible Strength in Concrete.
Grade of concrete
|
Permissible Strength
|
||
Due to bending
|
Direct comp.
|
Avr. Bond
Stress
|
|
1 : 3 :6
M ( 100 )
M ( 10 )
|
435 lbs
/inch2
30 kg/cm2
3.0 N /mm2
|
365 lbs
/in2
25 kg /cm2
2.5 N/mm2
|
60 lbs/in2
4.0 kg/cm2
0.4 N/mm2
|
1 : 2: 4
M (150)
M (15)
|
750lbs/in2
50 kg/cm2
4.0 N/mm2
|
580lbs/in2
40 kg/cm2
4.0 N/mm2
|
87 lbs/in2
6.0 kg/cm2
0.6 N/mm2
|
1 : 15 : 3
M (200)
M (20)
|
1000lbs/in2
70 kg/cm2
7.0 N/mm2
|
760lbs/in2
50 kg/cm2
5.0 N/mm2
|
115 lbs/in2
8.0 kg/cm2
0.8 N/mm2
|
1 : 1 : 2
M (250)
M (25)
|
1250lbs/in2
85 kg/cm2
8.5 N/mm2
|
900 lbs/in2
60 kg/cm2
6.0 N/mm2
|
130 lbs/in2
9.0 kg/cm2
0.9 N/mm2
|
1
Cylinders are also prepared to find the compression strength of the concrete .The length of such cylinder is 30 cm (12 inches ) and diameter is 15 cm (6 inches).These are tested by placing them vertically in compression testing machine. The strength at which this cylinder break , that strength is divided by the cross-sectional area to find the crushing strength of the cylinder .
. Compressive Strength of Concrete
Concrete is basically used to withstand compression. Therefore it is tested in respect of its strength. Its cubes of 15 * 15 * 15 cm (6 * 6 * 6 inch) cube are made of the cube and they are cured for 28 days. Then they are tested under compression testing machine and its strength is compared with the standard strength of concrete. The load used to break the cube is divided by the area of x-section and the maximum stress is calculated .This maximum stress is called the ultimate strength or the crushing strength of the concrete. This strength is called characteristic strength.Cylinders are also prepared to find the compression strength of the concrete .The length of such cylinder is 30 cm (12 inches ) and diameter is 15 cm (6 inches).These are tested by placing them vertically in compression testing machine. The strength at which this cylinder break , that strength is divided by the cross-sectional area to find the crushing strength of the cylinder .
Tensile Strength of Concrete
Concrete is weak in tension. Therefore, steel is used in concrete at the places of tension. The tension strength in concrete is about on to tenth of compression. Concrete cylinder is prepared to find the tension strength in concrete. Their split test is performed Since in design the tensile strength in concrete is neglected, therefore, this test is not considered of much importance.MODULAR RATIO for Strength of Concrete.
The modulus of elasticity of steel and concrete in R.C.C is called modular ratio .The ratio of stress to strain in a material is known as modulus of Elasticity of the material. It is mathematical expressed as
Modulus of
Elasticity =
Stress
Strain
E = f
e
The values of modulus of Elasticity in R.C.C are
different. The Modulus of Elasticity of steel (Es) is the ratio of the maximum stress
(fs) and strain (e) produced in it , i.e. .,
Es = fc
e
Steel and concrete unite in R.C.C to withstand the external forces. Therefore, the value of strain produced in them is same .In this case
E = fs = fc
E = fs = fc
Es Ec
And
fc = fs * Ec
Es
= fs / Es
Ec
= fs , (where
m= Es/Ec )
m
or
fc = fs
m
this shown that the capacity of concrete sticking with steel is equal to fs /m .This is assumed only in the method of elastic. Theory of design. Modular ratio is not used in the Load Factor Method of design
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this shown that the capacity of concrete sticking with steel is equal to fs /m .This is assumed only in the method of elastic. Theory of design. Modular ratio is not used in the Load Factor Method of design
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