Reveal a general rule in many industry concrete strength of 28 days strength is the standard

Reveal a general rule in many industry concrete strength of 28 days strength is the standard
Concrete hydration reaction is increased with time and gradually improve, under normal maintenance in the first seven days compressive strength is growing rapidly, after seven days to 14 days between slower growth, grow more slowly after 23 days, that is, the compressive strength of 28 days, although can be improved, but also is less, so in the strength of the 28 days compressive strength as a standard.