You CAN pour concrete over concrete.

More Info: Known as resurfacing, you can pour concrete over concrete as long as the original slab is structurally sound.  Overpouring old concrete with new concrete will give an old slab a fresh new look and cover any minor imperfections.

What Is Concrete?

Concrete is a composite substance, that is, it is made up of more than one material.  The three basic ingredients in a concrete mixture are cement, aggregate, and water.  The aggregate portion is often a mixture itself of sand, gravel, crushed rocks, and even recycled cement.  Depending on the application, additives are often combined with the basic concrete mixture such as fly ash, which replaces cement and lowers the cost of the project, or small river stones, which can be added to the top layer of concrete for a decorative effect.

How Concrete Works

The European Federation for Precast Concrete estimates that the worldwide consumption of concrete is 21 to 31 billion tons annually, placing it only second to water as the Earth's most consumed substance.

Making concrete utilizes a process called hydration.  Hydration is a reaction that occurs between Portland cement and water where water crystals grow and intertwine with the cement sand and gravel amalgamating them.  At the right temperature this process will slowly cure the cement mixture and harden it into a solid mass.