Hydration is the process that causes refractory concrete to:

Hydrationrefers to the chemical reaction between water and cement components in refractory concretes (hydraulic bonded castables), resulting in the formation ofcalcium-aluminate hydrates, which are responsible for initial strength—known asgreen strength. This strength enables the lining to be demolded and eventually dried without mechanical failure.

Hydration is not related to final heat resistance or dryout; those come later during the firing or heat-up stages. It is distinct from setting in air-setting refractories or sintering in ceramic-bonded types.