UFC 3-250-03
15 May 2001
CHAPTER 2
HOT-MIX ASPHALT
1. GENERAL. Hot-mix asphalt is often used for high-performance pavements. The degree of
performance required should be selected based on traffic conditions and the availability of satisfactory
materials. Hot-mix asphalt mixtures consist of mineral aggregate and asphalt cement. These hot-mix
asphalt mixtures are particularly suitable for airfield pavements, roads and streets, and storage areas. In
general, from 3 to 6 percent asphalt is required for asphalt base or intermediate courses, 4 to 7 percent
asphalt cement for surface courses, and 5 to 7 percent for porous friction courses. However, the
optimum asphalt content should be determined according to appropriate mix design procedures. The
aggregate gradations specified for hot-mix asphalt pavements are shown in table 2-1.
a. Advantages and Disadvantages. The hot-mix method of preparing paving mixtures provides for
thorough coating of the aggregates with a uniform film of asphalt cement and accurate control of
aggregate sizes and quantity of asphalt cement. Hot-mix pavements require no curing period after being
laid and can be used as soon as the pavement has cooled. The paving mixture must be rolled to
compact the mix while sufficiently hot because rolling is relatively ineffective after the mixture has cooled
and the required density will not be achieved. Hot-mix pavements can be constructed rapidly with a
minimum probability of damage to unfinished pavements from unfavorable weather conditions.
Immediately after adequate rolling and a cooling period, the pavement has a high degree of stability from
the interlocking of the coarse and fine aggregate and adhesion of the asphalt cement, as well as a high
resistance to moisture penetration and frost damage.
b. Uses. Hot-mix asphalt paving mixtures can be designed that are satisfactory for an asphalt
base course, intermediate course, surface course, or porous friction course. Wheel loads, wheel
spacing, tire pressures, intensity of traffic, and subgrade strength (California bearing ratio (CBR)) dictate
the thickness of pavement (TM 5-825-2/AFJMAN 32-1014). Normally, asphalt base courses of any
desired total thickness may be constructed in layers up to 150 millimeters (6 inches) thick. For airfield
pavement applications hot-mix asphalt will be used as the intermediate and surface courses on types A,
B, C, and D traffic areas, blast areas, and any other areas (even non-traffic) where their use is
economical. The four types of airfield traffic areas (A, B, C, and D) are described in TI 825-07
(AFMAN 32-1123(I)) and TM 5-824-1/ AFJMAN 32-8008 V1. Hot-mix asphalt can be used on any road
or street classification A through F (see TM 5-822-2/AFM 88-7, Chap. 5 (Future AFJMAN 32-1125(I)).
Porous friction courses shall be used primarily to prevent hydroplaning on runways or other high-speed
pavements. Areas subjected to fuel spills will require an application of a coal tar sealer to protect the
hot-mix asphalt pavement. When possible, the use of a rigid pavement should be investigated. Stone
Matrix Asphalt is used in applications requiring a rut and abrasion resistant surfacing.
2.
EQUIPMENT.
a. Plant Equipment. The purpose of an asphalt plant is to produce a mixture properly coated with
asphalt cement that consistently meets the requirements specified in the job mix formula (JMF) for
aggregate gradation, asphalt content, and temperature. Control of the asphalt mixture quality must be
initiated at the aggregate stockpiles. Each aggregate stockpile should be stored to prevent segregation
or mixing with adjacent stockpiles.
2-1
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