By adding water, the cement powder is mixed into a cement paste, which hardens by hydration both in the air and under water. During the hardening process, the cement paste becomes a so-called cement stone, which also remains hard under water.
Cement is classified by its integral parts, strength development and hardening behavior. Components of the cement may be, for example, Portland cement clinker, slag sand, limestone or fly ash. The hardening process can be divided into fast, normal or slow hardening cement.