GRADES OF CONCRETE

• Compressive strength of concrete is the most important property of concrete. Because other properties like tensile strength, shear strength, density, impermeability, durability etc. can be inferred from the compressive strength using established correlations.
• Compressive strength can be measured by standard test on concrete cube, or cylinder specimen.
• Strength of concrete in uniaxial compression is determined by loading standard test cube ( 150 mm size ) to failure in compression testing machine.

• The test specimen in generally tested 28 days after casting (and continuous curing)
• Cube is always tested on sides i.e., face in touch with mould.
• Strength of cube is expressed to the nearest of 0.5 n/mm².
• As per IS 456 : 2000 three specimen of a sample is taken.
• Additional samples may be required for various purposes such as to determine the strength of concrete at 7 days or at the time of striking the from work, or to determine the duration of curing, or to check the testing error. Additional specimen may also be required for testing samples curved by accelerated methods.
• To report, strength of cube, we take average of three specimens of a sample.
• Individual variation should not be more than ± 15% of average if variation is more, test results of the sample are invalid.