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Concrete doesn’t dry; it cures.

Concrete gains strength through a chemical reaction between cement and water. After pouring, concrete is often kept wet (moist-cured) for an extended period to prolong the chemical reaction (thereby strengthening the product), and to keep outer portions of the concrete from drying out long before interior portions (thereby minimizing cracking). Design calculations for concrete construction typically are based on the strength expected after 28 days of curing. However, the maximum strength of a very large pour might not be achieved for decades.

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