A.Bill Palmer responds: To start with, a set retarder does nothing to help concrete cure. It simply makes the concrete set more slowly, which would actually make proper curing a more critical concern, since the concrete would have more time to dry out.
For concrete to reach its full strength, it needs water to hydrate the cement. If it dries out, then the resulting concrete is soft, even chalky in an extreme case. This is most common on the surface of a slab. If it dries out even momentarily, it will be weakened (a condition called dusting).
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