I took concrete design courses in college and designed concrete in a previous life but I have probably forgotten more than I remember. I do know that moisture must be present for hydration to occur in concrete. Temperatures must also be within the allowable range (hydration really slows down below 40°F and essentially stops at and below 32°F). Once the cement in the concrete has fully hydrated the hydration process will cease.

My feelings are that concrete hydration may continue for several months or even years under ideal conditions but that the concrete will only slightly (even negligibally) increase in strength after a certain point.

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