2.2 Types of Flexible Pavements
These pavements may fall into one of the following categories:
- surface-treatment on a granular base,
- thin hot-mix asphalt (< 2 in.) on a granular base,
- intermediate hot-mix asphalt (2 - 4 in.) on a granular base,
- thick hot-mix asphalt (> 4 in.) (semi-rigid),
- thin hot-mix asphalt on a chemically stabilized base or subbase (semi-rigid),
- thin hot-mix asphalt on an asphaltic bound base (semi-rigid).
Stabilization of the subgrade layer can be used with any of the above pavement types. Typical stabilizers include asphalt cement (for base only), lime, cement, fly ash, or lime-fly ash combinations.
2.2.1 Perpetual (HMA) Pavements
Perpetual pavements take into account the increased structural demands due to heavy truck traffic, where cumulative one-direction traffic loading of more than 30 million ESALs over a 20-30 year design life is projected. By limiting the strain level at critical locations, these pavements are designed to have a virtually infinite fatigue and rut life, requiring only periodic surface renewal.
For designing perpetual pavements using FPS 21, see Section 6,