Asphalt is composed of the following:
a) mineral aggregate – stone, sand
b) asphalt binder – petroleum derivative
Asphalt pavement is a mixture of stone, sand, and asphaltic binder, with the bituminous material comprising between 4% and 0% of the total. Most asphalts are mixed, heated, and blended in a batch plant. The asphalt is then hauled and spread to a uniform depth and rolled until compacted.
- 6-10 Inches Compacted Base
- 3-4 Inches Rock or Crush n Run
- 2 Inches Binder
- 3 Inches Topping or Finish Coat (Typical Application Conditions Vary)
Failures in the construction of an asphalt pavement may be attributed to:
- insufficient or improperly compacted base
- poor drainage
- over-compaction or under-compaction of asphalt
- asphalt is not at optimum temperature when applied
A good asphalt pavement seldom wears out, it is destroyed by external factors.
- water penetrates asphalt and destroys base
- sunlight (oxidation)breaks down the liquid asphalt that holds the aggregate together – causes raveling and shrinking cracks invites water
- petroleum spills – gas and oil spots soften the asphalt
TYPES OF ASPHALT DETERIORATION
- alligatored (areas of connecting cracks)
- slippage (typical of improper compaction)
- reflection (older cracks occurring in new overlay) – edge joint
- channels or ruts
- corrugations and shoving – grade depressions
- utility cut depressions
- gas and oil spillage
The process of deterioration begins as soon as the asphalt is put down. In normal conditions, after 3 to 5 years major deterioration is taking place.
- oxidation (sunlight) is causing asphalt to turn gray and brittle, resulting in cracking.
- water is entering cracks, freezing during the freeze/thaw cycle, and causing larger cracks and potholes.
- rain is entering cracks and causing base damage.