30 June 2001
materials, and inadequate durability when exposed to freezing and thawing or sulfates. The result has
been unsatisfactory performance, increased maintenance, and dissatisfied users in some cases. The
designer should be certain to consult current versions of each service's guide specification and TM 5-
822-7/AFM 88-6, Chapter 8, for assistance in preparing project specifications.
4. ASPHALTIC CONCRETE. Asphaltic Concrete is the normal surfacing for flexible pavements.
Unlike portland cement concrete, it normally functions as a relatively thin wearing surface and is not the
major structural element of the pavement. Asphaltic concrete on airfields is exposed to much more
severe loads than on highways and is quite different from highway asphaltic concrete mixes.
Substitution of asphaltic concrete highway mixes for asphaltic concrete airfield mixes is not acceptable
and is a major engineering blunder. The requirements of TM 822-08/AFMAN 32-1131 V8(1)/DM 21.11
will provide an asphaltic concrete that will stand up to the loads of modern military aircraft in all
a. Constituents. Asphaltic concrete is composed of well-graded aggregates (approximately
95 percent by weight) and an asphalt cement binder (approximately 5 percent by weight).
(1) Binder. Asphalt cement from the distillation of petroleum is the most common binder in
asphaltic concrete. Liquid asphalts from emulsifying asphalt cement with water or dissolving the asphalt
cement in a solvent have many applications in pavements but are not normally used as a binder for high-
quality airfield pavements. Tars from the distillation of coal are seldom used as binder in airfield
pavements today. There are also natural asphalts that occasionally are used as binder material for
(a) Characteristics. Asphalt is a complex hydrocarbon product whose composition and
properties vary depending on the petroleum source and distillation process. Asphalt is probably the
most viscoelastic material used by civil engineers in routine construction. Its stiffness increases as its
temperature drops or as the speed of loading increases, and in reverse the stiffness drops as
temperature increases or as the speed of loading is slowed. Asphalt cement functions as a cohesive
binder for the aggregate and helps provide a nominally waterproof surface.
(b) Specification. The asphalt binder should be specified in accordance with the new
Strategic Highway Research Program (SHRP) pavement grading (PG) system (AASHTO PP6). This
new system matches specific characteristics of the asphalt cement with environmental exposure
conditions. This improved matching of binder properties and project environmental conditions should
extend the effective life of asphaltic concrete pavements. TM 822-08/AFMAN 32-1131 V8(1)/DM 21.11
provides guidance on selecting PG grades of asphalt cement for different project locations. SHRP PG
grading is not used universally worldwide, therefore alternate specification methods based on viscosity
(ASTM D 3381) and penetration (ASTM D 946) can be substituted depending on the local market
practice. Polymer additives are increasingly being used with asphalt binders and have been particularly
effective for enhancing cold-weather properties. This is an evolving area so TM 822-08/AFMAN 32-1131
V8(1)/DM 21.11 and HQUSACE (CEMP-ET), appropriate Air Force MAJCOM pavements engineer, or
Naval Facilities Engineering Service Center should be consulted for up-to-date guidance.
(2) Aggregates. The deformation resistance of asphalt concrete exposed to military aircraft
traffic is primarily a function of the aggregate, and the binder's contribution is secondary in comparison.
The aggregate gradation, particle shape, and control of these parameters during production are crucial
in providing an asphalt concrete that will resist the high tire pressure of modern military aircraft. Limiting
the natural sand that has rounded particles to no more than 15 percent of the total aggregate by weight
is an important requirement in the military requirements for asphalt concrete for military airfields. At