Calcium silicates in cement react with water to form calcium silicate hydrate, the gel that binds the mix, along with calcium hydroxide and heat. Concrete hardens through this reaction, not by drying, so it keeps gaining strength for weeks and months as long as moisture and warmth last. The heat released is what makes mass pours run hot in the core and lets blankets keep a winter slab from freezing.
Leave the blankets on, hydration is the only heat that slab has until the sun comes up.
Saying concrete dries is the giveaway of an outsider: it cures, and drying it out early stops its strength gain.
Also heard as
- cement hydration
Do not mix it up with
- Curing: Hydration is the chemical reaction itself; curing is what the crew does to keep moisture and temperature right so hydration can continue.
Related terms
Portland cement
The gray powder that reacts with water to bind sand and stone together into concrete.
Curing
Keeping fresh concrete moist and warm enough, for long enough, that the cement keeps hydrating.
Initial set
The point at which fresh concrete stops being workable and begins to stiffen into a solid.
Maturity method
Estimating in-place concrete strength from its temperature history, recorded by sensors cast into the pour.