Concrete hardens rapidly at first and then the process slows down. The actual curing time for concrete varies, dependent on weather conditions, temperature, mixture proportions, the size and shape of the concrete area, and the specified strength of the concrete.
Many websites specify a curing time of 28 days, but this is not long enough for the cement to reach full strength. The American Concrete Association Committee 301 indicates that ASTM C 150 Types I, II, III, IV, and V cement will reach 70 percent of strength within 14 days, with some types reaching this point earlier than others. If using moist-curing for at least the first week, cement may see an additional strength increase of 50% or more by the 90 day point.
To learn more about different cements, the impact of factors such as temperature, curing times, and how to maximize the strength of your concrete, visit our article on cement and concrete.