Asphalt will decay because of factors above the surface and factors below the surface. A well-designed and well-constructed asphalt pavement structure will be better able to resist above-surface decay contributors. During construction, the asphalt should have an appropriate type of sub-base rock, which should be compacted properly. During installation of the asphalt surface, the mix should retain an appropriate amount of heat (above 200 degrees) before it is compacted, and the material should be compacted with proper equipment. Above-surface factors that contribute to asphalt decay are: rainfall, freeze-thaw cycles, snow and ice, foreign substances such as sand, salt and oil or gas leaks, sun oxidation, heavy equipment or vehicles.