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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 »

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Construction Noise

Noise Basics Healthy humans can hear audible sound with a range of 20 Hz to 20,000 Hz with a maximum intensity at 3,000 Hz. (Hz = Hertz, or cycles per second.) Frequencies below 20 Hz are called “infrasound” and above 20,000 Hz “ultrasound.” The numerical magnitude of a sound typically expressed as sound pressure level … 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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HMA Placement

Mix placement and compaction are the two most important elements in HMA pavement construction. Mix placement involves any equipment or procedures used to place the delivered HMA on the desired surface at the desired thickness. Mix placement can involve complicated asphalt paver operations or simple manual shoveling. This section provides a basic description of HMA … Read more »

Figure 3. Limerock base course undergoing final grading.

HMA Pavement

HMA pavements are classified as “flexible” pavements because the total pavement structure deflects, or flexes, under loading. A flexible pavement structure is typically composed of several layers of material. Each layer receives the loads from the above layer, spreads them out, then passes on these loads to the next layer below. Thus, the further down … Read more »

Figure 12: Cutting equipment for one dowel bar slot at a time.

Dowel Bar Retrofit Construction Practices

Introduction The following describes and illustrates the dowel bar retrofit construction process. In addition, descriptions of critical details for ensuring pavement performance are also included. In general, the dowel bar retrofit process includes the following steps: Using diamond saw blades, sawcut dowel bar slots (three to four per wheelpath). Remove existing concrete within dowel bar … Read more »

Figure 2. Large vibratory steel wheel roller (17 tonnes (18.7 tons), 213 cm (84-inch) wide drum).

Compaction Equipment

There are three basic pieces of equipment available for HMA compaction: (1) the paver screed, (2) the steel wheel roller and (3) the pneumatic tire roller.  Each piece of equipment compacts the HMA by two principal means: By applying its weight to the HMA surface and compressing the material underneath the ground contact area.  Since … Read more »

Figure 2. Side tie bar inserter.

Tie Bar Placement

Tie bars are typically placed after PCC placement either by hand or using a tie bar inserter attachment (slipform paving only). When one lane at a time is paved, tie bars are inserted at mid-slab depth and bent back until the adjacent lane is ready to be paved (see Figure 1). On slipform pavers, tie … Read more »

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