Concrete is made up of rock, sand, and Portland- (Lime and silica make up about 85% of the mass) all of the materials are porous allowing water to migrate in to and through the concrete.
If you are in a southern state no problem but if you are in an area that freezes with precipitation we have a problem. Using a poor quality rock like lime stone rock which absorbs water.
When the concrete freezes the water inside the lime rock expands it blows the surface off the concrete.
The only way to slow down/stop this from happening is to seal the surface of the concrete. Like -Enviroseal 20 is a clear, water based 20% alkylalkoxysilane penetrating sealer. It protects against moisture and chloride intrusion.
There are many grades of concrete check the next post for more information.