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Lab/Field Technician

Any individual who performs laboratory or field testing of paving materials. This includes individuals who collect material samples for testing, which may be from the paving site, aggregate quarry, or production facility.
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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 7: Close-up of beam with the 4 clamps in place.

Flexural Fatigue

Overview The flexural fatigue test is used to characterize the fatigue life of HMA at intermediate pavement operating temperatures. This characterization is useful because it provides estimates of HMA pavement layer fatigue life under repeated traffic loading. In a well designed pavement, strains in the pavement are low enough so that fatigue is not a … Read more »

Figure 5: Hamburg Wheel Tracking Device (HWTD) from (Stuart and Youtcheff, 2002).

Laboratory Wheel Tracking Devices

Overview Laboratory wheel-tracking devices (Figure 1) are used to run simulative tests that measure HMA qualities by rolling a small loaded wheel device repeatedly across a prepared HMA specimen. Performance of the test specimen is then correlated to actual in-service pavement performance. Laboratory wheel-tracking devices can be used to make rutting, fatigue, moisture susceptibility and … 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 9: Inserting the sample into the hot ignition oven.

Binder Content

Overview Asphalt binder content affects HMA mixture performance in the areas of stiffness, strength, durability, fatigue life, raveling, rutting and moisture damage. Therefore, it is important in HMA quality assurance, pavement forensic investigations and HMA research. The ignition test is the most common method used to determine HMA asphalt binder content. In the ignition method … 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 7: Soaking the sample.

Coarse Aggregate Specific Gravity

Overview The coarse aggregate specific gravity test (Figure 1) is used to calculate the specific gravity of a coarse aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water. It is similar in nature to the fine aggregate specific gravity test. … Read more »

Bulk Specific Gravity_FI

Bulk Specific Gravity

Overview The bulk specific gravity test is used to determine the specific gravity of a compacted HMA sample by determining the ratio of its weight to the weight of an equal volume of water. The bulk specific gravity test measures a HMA sample’s weight under three different conditions (Figure 1): Dry (no water in sample). … Read more »

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