Understanding Concrete
Concrete is like a sponge made of rock. It transforms a wet aggregate into what appears to be a dry impenetrable mass of solid rock. But it's not solid, nor is it impenetrable.
Pouring and curing of concrete
Water is essential in the mixing. As it cures water evaporates and leaves behind small capillary-type voids inside, like a sponge. Once cured, outside water then becomes a destructive element that can permeate the concrete, carrying with it salts and other chemicals that attack and destroy the integrity of the concrete. Outside water also leaches out soluble chemical components necessary for concrete integrity.