How long does concrete need to cure in order to reach 90% strength?
For getting 90% strength it should be cure for 20 days.
As we know that concrete attains 50% of its design strength when it cured for 3-7 Days.
75% of Compressive strength achieved in 14 days 90% of strength by 20 days as time goes on the strength increase gradually.
And 99% of strength by 28 days.