Compressive Strength of Concrete
It is one of the important property of concrete which other properties are related. Simple way to understand about the topic is Maximum strength of concrete. Since, tensile strength is almost zero, when we talk about the strength of concrete, it is compressive strength. It can be defined as the ability of concrete which can resist the gradual load. Compressive Strength is formed by performing test in universal compressive machine (UTM) over standard tube 150mm size (incase of cylinder it is D= 150 mm and H= 300 mm).
The test is performed at the age of 28 days in general but it can be done at the age of 3 days and 7 days if rate of gain of strength is also be found. Strength of cube is expected nearest to 0.5 N/mm2 .
As per IS 456, one sample must consist three specimen and average strength of these three specimen is taken as compressive strength of sample provided. Variation of strength of specimen is ±15%.
Note : Strength of Cylinder = 0.8 times Strengthen of Cube
Strength of Cube = 1.25 times Strength of Cylinder
Steel plate is kept because to transfer load uniformly during testing.
Characteristics Compressive Strength
It is strength below which not more than 5% of the test results are expected to fall. Concrete is designated by characteristics compressive strength at the age of 28 days.
Designing is done for targeted mean Strength.
Here, K depends upon % definition of characteristic strength.
