Can Water Damage Concrete?
Yes, water can damage concrete.
Considering only concrete that has already set and gone through the normal settling process, which will result in cracking no matter how good your contractor may be, outside water forces that are not part of the cement mixture can damage concrete as well.
How Good Was Your Concrete Contractor?
The future damage that your concrete will withstand will depend on how well it was set and sealed upon installation. Concrete can be as much as 12-20% air and as it dries the water evaporates to the surface forming air capillaries. These capillaries can then serve as aqueducts down the line if water permeates concrete that is not sealed properly.
Cracking occurs in concrete that is exposed to the elements in colder climates. Water penetrates the concretes through cracks and fissures and then begins a thaw-freeze cycle in which the water freezes and expands, cracking the concrete. It then thaws and refreezes repeatedly causing damage.
Efflorescence is a deposit of crystals on the surface of concrete as a result of the evaporation of salt-laden water. Efflorescence is driven by water that has permeated concrete and come in contact with any of a variety of water dispersible materials, the most common of which is calcium hydroxide. It can occur over time or as soon as the concrete is introduced to cool, moist conditions.
Here's how it works. Water brings the calcium hydroxide to the surface. Once it reaches the surface, it will mix with the carbon dioxide in the air. Once the two converge, they will convert to calcium carbonate and water.
Water Causes Rust
Generally, building codes require that that under certain conditions rebar be added to concrete for structural support. This is another instance where water will damage concrete through the rebar. Because rebar is metal, it begins to rust when exposed to water. Rust will grow and expand within your concrete causing it to crack.