Hydration is the chemical reaction between cement and water, in which new, hard crystals form that bind the grains together. This is the process by which concrete, mortar and cement-bound floors change from a workable mix into a rock-hard material. No hydration without water: the water is not only there for mixing, but is also the reaction partner of the cement.
Course of the process
- Setting — shortly after mixing the reaction begins; the mix loses its workability and becomes stiff
- Hardening — after that the strength increases as more cement hydrates
- Continuing strength growth — concrete reaches its standardised strength after 28 days, but hydration continues long afterwards, as long as moisture is present
The reaction releases heat (heat of hydration). In large, massive concrete pours this heat can rise high and cause cracking; this is taken into account in the design.
Importance in practice
- Curing — fresh concrete must be kept moist so that hydration can continue and the surface does not dry out too quickly
- Water-cement ratio — too much water weakens the concrete, too little water gives incomplete hydration
- Temperature — warmth accelerates hydration, cold slows it down; in frost the reaction can even come to a standstill
Good curing is decisive for the eventual strength and durability of the concrete.
Related terms
- Cement
- Concrete
- Mixing water
- Curing poured concrete
- Water-cement ratio
- Setting
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