Plant Operations
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
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
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
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
Mix Types
HMA Mix Types The most common type of flexible pavement surfacing in the U.S. is hot mix asphalt (HMA). Hot mix asphalt is known by many different names such as hot mix, asphalt concrete (AC or ACP), asphalt, blacktop or bitumen. For clarity, this Guide makes a conscious effort to consistently refer to this material … Read more
Key Pollution Concepts
Introduction The connection between pavement and pollution may not be immediately obvious. However, the United States has nearly four million miles of roads. (Low Impact Development Center, Inc. et. al.[1]) In a very simple breakdown, people drive and goods are transported on these roads; burning of fossil fuels in engines creates air pollution, while rain … Read more
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
Aggregate Segregation
“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
Stone Matrix Asphalt
Stone matrix asphalt (SMA) is a gap-graded HMA (Figure 1) that is designed to maximize deformation (rutting) resistance and durability by using a structural basis of stone-on-stone contact (Figures 2-6). Because the aggregates are all in contact, rut resistance relies on aggregate properties rather than asphalt binder properties. Since aggregates do not deform as much … Read more
Open-Graded
An open-graded HMA mixture is designed to be water permeable (dense-graded and SMA mixes usually are not permeable). Open-graded mixes use only crushed stone (or gravel) and a small percentage of manufactured sands. There are two types of open-graded mixes typically used in the U.S.: Open-graded friction course (OGFC). Typically 15 percent air voids, no … Read more
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