Figure 1. The 3 stages of cement hydration (Longarini, Nicola & Crespi, Pietro & Zucca, Marco & Giordano, Nicola & G., Silvestro. (2014). The use of fly ash in high strength concrete mix design.)
Ideally you want all of the water in your mix to be involved in the hydration of the cement as this would give the maxiumim strength. Most of the water will be incorporated, but a large % will be lost by evaporation which means hydration and therefore strength will not reach the maxmimum. This problem is more severe in large shallow pieces of concrete on hot days - the concrete will dry out but will not be fully cured.
As soon as the concrete has hardened (24-48h) you must replace the water lost by evaporation by keeping the concrete as wet as possible.
Keep it wet by…
- Pouring water on, or spraying with a hose periodically
- Fully submerge in a water bath (if the piece is small enough)
- let it get rained on
Stop it drying out by…
- Keeping it covered with tarpoline
- Cover with a damp sheet
Figure 2. Moisture cured vs air dryed concrete (source)
For maxium strength…
• In the mix - minimum water
• After 24-48h - maxium water