There are two HMA mix design methods: SUPERPAVE® and Marshall. Given the extent of testing that each method has undergone, rest assured that either one will meet your needs.
With the SUPERPAVE® method, samples are compacted using a gyratory compactor and are then tested for volumetric properties. SUPERPAVE® was developed about 20 years ago under the Strategic Highway Research Program to give highway engineers and contractors the tools they need to design asphalt pavements that will perform best under extremes of temperature and heavy traffic loads.
With the Marshall method, mixes are designed using impact compaction. This method was developed over 50 years ago by the U.S. Army Corps of Engineers and has been adopted by the Asphalt Institute. It is used to design mixes for highway pavements in the United States and abroad.
For driveways and parking lots, there are two basic layers of pavement: the wearing course and the base course.
The wearing course is the top layer of a pavement system designed to create a smooth riding surface and to seal the surface from water penetration. The two most common asphalt wearing courses have a nominal maximum aggregate size of 9.5mm (3/8 inch) and are called 9.5mm and ID-2 wearing. There is also a heavy-duty wearing course called ID-3, often used in place of 9.5mm or ID-2 when additional strength is needed (e.g., for private lanes, farms, parking lots). ID-3 has a nominal maximum aggregate size of 19mm (3/4 inch). A wearing course may be used by itself as the only layer of pavement for a driveway or parking lot, provided the stone subbase is adequate.
The base course is the bottom layer of a pavement system designed to create a strong foundation for the wearing course. The two most common base courses are 25mm and Bituminous Concrete Base Course (BCBC), with a nominal maximum aggregate size of 25mm (1 inch). A base course should not be used by itself, as it will begin to deteriorate if the wearing course is not applied within a few years.
|Method of Mix Design||Course Type||Mix Design|
|Marshall||Wearing Course, Heavy-Duty||ID-3|
Summary of HMA mix designs and pavement courses.
Pavement systems have three distinct components: subgrade, (stone) subbase, and Hot-Mix Asphalt. Functionally, the subgrade is like the footer of a house, the subbase is like the foundation, and the Hot-Mix Asphalt is like the house itself. If the footer or foundation of a house is improperly installed, the entire structure will fail. The same is true for your pavement system.
The first component of a pavement system is the subgrade. It is the underlying soil prepared to support the pavement structure. Your EBY estimator will determine the suitability of the existing subgrade.
The second component of a pavement system is the subbase. It is the layer immediately above the subgrade, typically consisting of a coarse aggregate such as 2A or 2RC stone. This layer is critical to the overall strength of the structure. Your EBY estimator will determine the suitability of the existing stone subbase. If there is none, the estimator will recommend the type of stone and the thickness (full-compaction depth) best suited for your driveway, parking lot, or other application.
The third component of a pavement system is the Hot-Mix Asphalt (HMA). Pavement designers specify different HMA mixture types, depending on the type of project or application. HMA is referred to as asphalt pavement, blacktop, or macadam. Your EBY estimator will recommend the type of mixture and the thickness (full-compaction depth) best suited for your driveway, parking lot, or other application.
|Application||Stone Subbase||Base Course||Wearing Course|
|Minimum-use driveway||2RC or 2A stone; 6" thick||not typically used||9.5mm, ID-2, or ID-3; 2" thick|
|Standard driveway||2RC or 2A stone; 6" thick||not typically used||9.5mm, ID-2, or ID-3; 2.5-3" thick|
|Premium driveway||2RC or 2A stone; 6" thick||25mm or BCBC; 2-2.5" thick||9.5mm or ID-2; 1.5" thick|
|Standard parking lot||2RC or 2A stone; 6" thick||not typically used||9.5mm or ID-2; 3 in. ID-3; 3-4" thick|
|Premium parking lot||2RC or 2A stone; 6-8" thick||25mm or BCBC; 2-4.5" thick||9.5mm or ID-2; 1.5-2" thick|
|Street||2RC or 2A stone; 6-10" thick||25mm or BCBC; 4-5" thick||9.5mm or ID-2; 1.5-2" thick|
Pavement courses and thickness, by application type. Thickness is the full-compaction depth.
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