by Concrete gradually hardens and increases its compressive strength through the bonding effect of cement.
Due to the fact that the hardening of cement is not achieved overnight, but gradually becomes perfect over time.
Under normal maintenance conditions, the compressive strength increases rapidly in the first seven days, slightly slower between 7-14 days, and even slower after 28 days.
That is to say, the compressive strength after 28 days is the standard strength, which serves as the standard for design and construction quality inspection.
Obviously, if a strength of less than 28 days is used as the standard strength, the performance of concrete will not be fully utilized.
If a strength greater than 28 days is used as the standard strength, although the performance of concrete can be fully utilized, the long time to reach the standard strength affects the construction progress.
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