For the same reason wood is painted, asphalt should be sealed. Without protection, the elements of rain, sun and snow will penetrate, oxidize and deteriorate asphalt. When your pavement is new, it is flexible. That is one of the reasons asphalt is used in cold weather climates–it has the ability to flex when the ground freezes. Over time, an unprotected surface becomes more brittle due to the harmful effects of nature, and when it has lost its flexibility, it cracks. Once cracking begins, water can penetrate to the sub-base, leading to wider deterioration of the pavement surface. Water penetration is the number one reason for pavement failure.