2 questions really
Sometimes it has to be kept wet, other times not. Does the atmospheric temperature & humidity affect how long it takes to cure, and how strong it will be?
I remember needing to wet down a new patio regularly as it set up, but this isn’t done with streets, sidewalks, or poured buildings.
In: Chemistry
The reaction that “sets” concrete is called hydration…the portland cement is literally bonding with water molecules. Without water, it will not react. If it dries out before all the cement has bonded, it will be weak.
Temperature & humidity effect how fast water evaporates from the surface. This doesn’t usually matter if the mix is really wet (lots of excess water) but if it’s pretty dry then you could lose water too fast, before it fully hydrates, and then you get weaker concrete.
Temperature also impacts how fast the hydration reaction happens (hotter = faster) so, regardless of humidity, higher temperature will lead to faster cure. The chemical reaction is also exothermic (generates heat) so large volumes of curing concrete can self-heat. If they get hot enough to boil the water before it can hydrate, that’s also a problem. Large concrete pours may need cooling for this reason.
Whoever designed the concrete should take all this into account. If you don’t need the strength hit you get from not keeping it properly moist during cure, like a sidewalk, you don’t need to bother. Poured buildings are usually pouring into a form where they can’t lose water from most of the surface (and will often pool water or plastic over the top to minimize evaporation).
Very high strength concrete, like skyscrapers or dams, will have carefully design temperature, protection, and moisture profiles, backed up by testing, to make sure that the concrete actually gets to the strength it needs to. High strength concrete cures slooooooooowly.
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