Cavity / Air entrapment in concrete (unwanted)

When placing the concrete, air-filled cavities may develop. These air voids (blowholes, air pockets, air bubbles, entrapped air, air entrainments, etc.) may affect the surface appearance (depressions) or can be invisible/nearly invisible as a thin layer of cement paste covers them. In order to fill these surface voids, the concrete surfaces must be treated mechanically (e.g. using a sandblaster) and levelled out in the following. By compaction of concrete, the unwanted air will be released.