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Asphalt Paver Operator

Any worker who operates an asphalt paver or one of its major components. This includes individuals such as the screed arm operator and automation specialist.
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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 »

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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 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 1: 6-inch ACB layer under 1.5 inches of State Mix IV (Coin Shown is a Quarter)

Asphalt Concrete Base (ACB)

Asphalt concrete base (ACB), also called asphalt treated base (ATB), is a dense-graded HMA with a larger nominal maximum aggregate size (1 inch) intended for use as a base course or binder course (see Figure 1). In addition to site paving benefits, ACB can be advantageous because it can provide: A waterproof barrier to prevent … Read more »

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Cold In-Place Recycling

Cold in-place recycling (CIR) is the processing and treatment with bituminous and/or chemical additives of existing HMA pavements without heating to produce a restored pavement layer (AASHTO, 1998[1]). It involves the same process of cold plant mix recycling except that it is done in-place by a train of equipment. Procedure The typical CIR process involves … Read more »

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Segregation in Transport

“Segregation” is a term often used in the HMA industry to describe a number of different phenomena. It’s most general definition comes from Stroup-Gardiner and Brown (2000[1]): “Segregation is a lack of homogeneity in the hot mix asphalt constituents of the in-place mat of such a magnitude that there is a reasonable expectation of accelerated … Read more »

Figure 17. Automatic grade control using a mobile reference beam.

Asphalt Paver

In 1934 Barber-Greene introduced the Model 79 asphalt laydown machine, a self-propelled formless laydown machine with a floating screed (Tunnicliff, Beaty and Holt, 1974[1]). Since then, the basic concept of the asphalt paver has remained relatively unchanged: HMA is loaded in the front, carried to the rear by a set of flight feeders (conveyor belts), … Read more »

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