Concrete should be sealed for a number of reasons. Exterior concrete in areas with freeze-thaw cycles, like Colorado, should be sealed. Concrete is porous and absorbs liquids easily. In freeze-thaw climates, when liquid freezes it expands and can destroy the surface of unsealed concrete. Oil, salt, fertilizer, and other household chemicals can also discolor and damage unsealed concrete.
There are different types of sealers that affect the look of your concrete.
Chemically reactive sealers penetrate into the concrete and are typically nearly invisible.
Solvent-based acrylic resin sealers and epoxies enhance the color of your concrete and give it a high-gloss, wet look.
Urethane is available in a wide range of finishes, from matte to gloss.