Frosting resistance vacuum concrete
In order to remove any water not required for the hydration of fresh concrete, this can be treated using negative pressure. For this purpose, the concrete surface is covered with filter mats and a vacuum cover, and then a negative pressure is generated with the aid of a vacuum pump.
The resulting vacuum concrete is characterised by lower shrinkage cracking and good frost resistance. At the same time, the concrete obtains a particularly dense and wear-resistant surface. The increased initial strength also permits early use of the surface.
More about this on https://de.wikipedia.org/wiki/Liste_gebr%C3%A4uchlicher_Betone#Vakuumbeton