Page 313 - Planning and Design of Airports

Structural Design of Airport Pavements 271

FIGURE 7-4 FAARFIELD aircraft database window.

Design of Flexible Pavements
Flexible pavements consist of a bituminous wearing surface placed
upon a base course and, where required by subgrade conditions, a
subbase. The entire flexible-pavement structure is ultimately sup-
ported by the subgrade. The surface course prevents the penetration
of surface water to the base course, provides a smooth, well-bonded
surface free of loose particles, resists the shearing stresses caused by
aircraft loading, and furnishes a texture of nonskid qualities not caus-
ing undue tire wear. The course must also be resistant to fuel spillage
and other solvents in areas where maintenance may occur.
The base course is the major structural element of the pavement;
it has the function of distributing the wheel loads to the subbase and
subgrade. It must be designed to prevent failure in the subgrade,
withstand the stresses produced in the base course, resist vertical
pressures tending to produce consolidation and deformation of the
wearing course, and resist volume changes caused by fluctuations in
its moisture content.
Flexible pavement base courses are available in different compo-
sitions, or “types,” including:

1. Item P-208—Aggregate Base Course
2. Item P-209—Crushed Aggregate Base Course
3. Item P-211—Lime Rock Base Course
4. Item P-304—Cement Treated Base Course