Although the scientific basis for these relationships is not firmly established, they can be used with confidence as long as the limitations with such an approach are recognized. This means that the relationships between design inputs (e.g., loads, materials, layer configurations and environment) and pavement failure were determined using experience, experimentation or a combination of both. Many pavement structural design procedures use an empirical approach. However, some government agencies and many private owners do not have specified standard pavement structural designs. For instance, a local residential street subject to only a few heavy loads per week (i.e., school bus, garbage truck) does not warrant the expense and time of a mechanistic-empirical design approach.

Often the required level of design does not warrant the use of advanced equations or models. Often assumptions and design procedures are based on extremely local conditions, which may not be transferable. When using a design catalog, it is important to be aware of the author’s assumptions and design procedure. The pavement designs within these catalogs can be based on a number of different design methods ranging from mechanistic-empirical to historical experience. State and local agencies often include them in their design manuals. Typically, design catalogs contain a listing of common loading, environmental and service regimes and the corresponding recommended pavement structures. The simplest approach to HMA pavement structural design involves selecting a predetermined design from a catalog. The principal methods of structural design in use today are (from simplest to most complex) design catalogs, empirical and mechanistic-empirical. Calculations are chiefly concerned with traffic loading stresses other environmentally related stresses (such as temperature) are accounted for in mix design asphalt binder selection. Structural design is mainly concerned with determining appropriate layer thickness and composition. Structural design for rehabilitation is covered in Maintenance & Rehabilitation. This section is focused on the structural design of new pavement. This includes the surface course as well as any underlying base or subbase layers. The goal of structural design is to determine the number, material composition and thickness of the different layers within a pavement structure required to accommodate a given loading regime.

Pavement design aashto method