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Any college or university student with an interest in the paving industry (typically construction management or civil engineering majors).
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Geosynthetics

Geosynthetics in HMA Applications The primary purpose of incorporating geosynthetics in the pavement design process is to reduce reflective cracking in HMA overlays and to resist moisture intrusion into the underlying pavement structure. Geosynthetics can be part of an overall rehabilitation strategy that will as a minimum include the placement of a new wearing/surface course … Read more »

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General Guidance

  This is an informational resource on hot mix asphalt (HMA). It contains a general overview of all HMA aspects. It is intended to assist those who work with HMA in any way including architects, engineers, contractors, students, and homeowners. Pavement Checklist Pavement Distress Top-Down Cracking References Suggested Reading Asphalt Institute. (2001[1]). HMA Construction. Manual … Read more »

Figure 1: Stacked sieves used for a gradation and size test.

Gradation Test

Overview The gradation and size test (Figure 1) is used to determine aggregate particle size distribution. Size distribution is perhaps the single most important aggregate quality associated with the control of HMA mixtures. Aggregate gradation and size affect HMA volumetric properties as well as mixture permeability and workability. In a gradation and size analysis, a … Read more »

Figure 1: Pouring the aggregate sample into the sieve stack.

Sieve

A sieve is a mechanical device used to separate samples of different sizes. Sieve sizes typically used for Superpave mix design are 1½ in, 1.0 in, ¾ in, ½ in, 3/8 in, No. 4, No. 8, No. 16, No. 30, No. 50, No. 100 and No. 200 (37.5, 25.0, 19.0, 12.5, 9.5, 4.75, 2.36, 1.18, … Read more »

Figure 1: Fatigue cracking caused by stripping.

Moisture Susceptibility

Moisture susceptibility is a primary cause of distress in HMA pavements. HMA should not degrade substantially from moisture penetration into the mix. HMA mixtures may be considered susceptible to moisture if the internal asphalt binder-to-aggregate bond weakens in the presence of water. This weakening, if severe enough, can result in stripping (Figure 1). To measure … Read more »

Figure 1. Maximum theoretical specific gravity sample.

Theoretical Maximum Specific Gravity

Overview The theoretical maximum specific gravity (Gmm) of a HMA mixture is the specific gravity excluding air voids. Thus, theoretically, if all the air voids were eliminated from an HMA sample, the combined specific gravity of the remaining aggregate and asphalt binder would be the theoretical maximum specific gravity. Theoretical maximum specific gravity can be … Read more »

Figure 3. Superpave gyratory compactor sample (left) vs. Hveem/Marshall compactor sample (right).

Superpave Mix Design

One of the principal results from the Strategic Highway Research Program (SHRP) was the Superpave mix design method. The Superpave mix design method was designed to replace the Hveem and Marshall methods. The volumetric analysis common to the Hveem and Marshall methods provides the basis for the Superpave mix design method. The Superpave system ties … Read more »

Figure 1: HMA temperature vs. compaction aspects.

Factors Affecting Compaction

HMA compaction is influenced by a myriad of factors; some related to the environment, some determined by mix and structural design and some under contractor and agency control during construction (Table 1).   Table 1: Factors Affecting Compaction Environmental Factors Mix Property Factors Construction Factors Temperature Ground temperature Air temperature Wind speed Solar flux Aggregate … Read more »

Figure 1. Truck loading under a storage silo.

HMA Transport

Mix transport involves all actions and equipment required to convey HMA from a production facility to a paving site including truck loading, weighing and ticketing, hauling to the paving site, dumping of the mix into the paver or material transfer vehicle hopper, and truck return to the HMA production facility (Roberts et al., 1996[1]). Ideally, … Read more »

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HMA Placement Considerations

There are, of course, many considerations to take into account when placing HMA. Many are dependent upon local materials, weather, crew knowledge and training, and individual experience. This subsection presents a few of the basic considerations that apply in virtually all situations: Lift thickness. A “lift” refers to a layer of pavement as placed by … Read more »

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