Why do we use a 6 cube for the compressive strength test of a concrete?

[Sumit Civil]

Why do we use a 6 cube for the compressive strength test of a concrete?

 

[Harikiran N]

3 for 7 days and another 3 for 28 days

 

[Jayant Joshi]

3 Cubes are tested after 7 days, and three cubes are tested after 28 days,
We take average reading of three cubes.

 

[Dnyan Deshmukh]

as per IS code, the ultimate concrete acceptance criteria is, its compressive strength at 28 Days.

If you get a low strength, you should have additional set of cube to check in further days to ensure concrete attended its desired strength at later age.

if you do not have it, what you will do - it will be costlier affair.

It is good to cast more cubes so that you can verify concrete strength gain at various stages and detect if any issue with concrete production.