Hot Mix Asphalt Glossary of Asphalt Terms
American Association of State and Highway Transportation Officials.
A measure of the viscosity of asphalt with respect to time, measured in poises, conducted at 60°C (140°F). The test method utilizes a partial vacuum to induce flow in the viscometer. (1)
ADT or AADT
Average Daily Traffic.
A hard inert mineral material, such as gravel, crushed rock, slag, or crushed stone, used in pavement applications either by itself or for mixing with asphalt. (1)
Internal spaces in a compacted mix surrounded by asphalt-coated particles, expressed as a percentage by volume of the total compacted mix. (1)
Apparent Specific Gravity Of Asphalt Mixture
A ratio of the unit weight of an asphalt mixture (excluding voids permeable to water) to the unit weight of water.
Asphalt (asphalt cement)
A dark brown to black cementitious material in which the predominating constituents are bitumens, which occur in nature or are obtained in petroleum processing. Asphalt is a constituent in varying proportions of most crude petroleum and used for paving, roofing, industrial and other special purposes. (1)
Asphalt cement that is classified according to the Standard Specification for Performance Graded Asphalt Binder, AASHTO Designation MP1. It can be either unmodified or modified asphalt cement, as long as it complies with the specifications. (1)
A mixture of asphalt binder and aggregate thoroughly mixed and compacted into a mass. (1)
An emulsion of asphalt binder and water that contains a small amount of an emulsifying agent. Emulsified asphalt droplets may be of either the anionic (negative charge), cationic (positive charge) or nonionic (neutral). (1)
Asphalt Leveling Course
A course of hot mix asphalt of variable thickness used to eliminate irregularities in the contour of an existing surface prior to placing the subsequent course. (1)
Asphalt Pavement Structure
A pavement structure that is designed and constructed so that all courses above the subgrade are asphalt concrete (Full-Depth Asphalt Pavement). (1)
Pavements consisting of a surface course of asphalt concrete over supporting courses such as asphalt concrete bases, crushed stone, slag, gravel, Portland Cement Concrete (PCC), brick, or block pavement. (1)
Asphalt Prime Coat
An application of asphalt primer to an absorbent surface. It is used to prepare an untreated base for an asphalt surface. The prime penetrates or is mixed into the surface of the base and plugs the voids, hardens the top and helps bind it to the overlying asphalt course. (1)
The layer in the pavement system immediately below the binder and surface courses. It usually consists of crushed stone, although it may consist of crushed slag or other stabilized or unstabilized material. (1)
The hot mix asphalt course immediately below the surface course, generally consisting of larger aggregates and less asphalt (by weight) than the surface. (1)
A class of black or dark-colored (solid, semisolid, or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, of which asphalts, tars, pitches, and asphaltites are typical. (1)
Suitable material from sources outside the roadway prism used primarily for embankments. (1)
Bulk Specific Gravity Of Asphalt Mixture
Ratio of the unit weight of an asphalt mixture (including permeable and impermeable voids) to the unit weight of water.
A test used for evaluating bases, subbases, and subgrades for pavement thickness design it is a relative measure of the shear resistance of a soil (see Soils Manual, MS-10). CBR = load required to force a calibrated piston into a soil specimen / load required to force a like piston into a crushed stone specimen capacity and ride quality of the pavement system. (1)
Cement treated base
A base layer constructed with good quality, well-graded aggregate mixed with up to 6% cement.
Channeled depressions that sometimes develop in the wheel paths of an asphalt pavement. (1)
Aggregate retained on the 2.36 mm (No. 8) sieve. (1)
The act of compressing a given volume of material into a smaller volume. (1)
An aggregate that has a particle size distribution such that when it is compacted, the resulting voids between the aggregate particles, expressed as a percentage of the total space occupied by the material, are less than 10%. (1)
The total number of equivalent 80-kN (18,000-lb.), single-axle load applications (equivalent single axle loads) expected throughout the design period. (1)
The lane on which the greatest number of equivalent 80-kN (18,000-lb.) single axle loads (ESAL) is expected. This will normally be either lane of a two-lane roadway or the outside lane of a multi-lane highway. (1)
The number of years from the initial application of traffic until the first planned major resurfacing or overlay. This term should not be confused with pavement life or analysis period. Adding hot mix asphalt overlays as required will extend pavement life indefinitely or until geometric considerations (or other factors) make the pavement obsolete. (1)
Design Subgrade Resilient Modulus
The value of the Subgrade Resilient Modulus (MR) used for designing the pavement structure. It is a percentile value of the subgrade resilient modulus test data distribution that varies with design ESAL. (1)
The property of an asphalt pavement that represents its ability to resist disintegration by weathering and traffic. (1)
Ratio of the unit weight of an asphalt mixture (excluding voids permeable to asphalt) to the unit weight of water.
A mixture of asphalt cement with water. Asphalt emulsions are produced by adding a small amount of emulsifying soap to asphalt and water. The asphalt sets when the water evaporates.
Equivalent Single Axle Load. A unit used to quantify various types of axle loadings into a single design number for pavement design. Defined as one 18,000 pound four-tire dual axle load.
Aggregate passing the 2.36 mm (No. 8) sieve. (1)
One having a continuous grading in sizes of particles from coarse through fine with a predominance of fine sizes. (1)
A pavement structure that maintains intimate contact with and distributes loads to the subgrade and depends on aggregate interlock, particle friction, and cohesion for stability. HMA pavements are flexible pavements; PCC concrete is not. (2)
Full-Depth Asphalt Pavement
The term FULL-DEPTH (registered by the Asphalt Institute with the U.S. Patent Office) certifies that the pavement is one in which asphalt mixtures are employed for all courses above the subgrade or improved subgrade. A Full-Depth asphalt pavement is placed directly on the prepared subgrade. (1)
Fabric-like materials used in some pavement construction applications. Uses include stabilization of base materials to prevent migration into subgrades. (2)
Granular Material used to replace undesirable materials in the grade for a pavement. (2)
Granular Equivalent (GE)
Equates the thickness of each aggregate, hot mix asphalt, or other material to an equivalent thickness of Class 5 granular base material. Used for the Soil Factor and R-Value pavement thickness design procedures.
Two-axle, six-tire trucks or larger. Pickup, panel and light four-tire trucks are not included. Trucks with heavy-duty, wide-base tires are included. (1)
Hot Mix Asphalt (HMA)
High quality, thoroughly controlled hot mixture of asphalt binder (cement) and well-graded, high quality aggregate, which can be compacted into a uniform dense mass. (2)
In place, or in it’s original location. (2)
Job-mix formula. A recommended/approved proportion of aggregate & asphalt used for field Quality Control/Quality Assurance of HMA mixture production. (2)
A layer or course of paving material applied to a base or a previous layer. (1)
Load Equivalency Factor (LEF)
The number of 80-kN (18,000-lb.) single-axle load applications (ESAL) contributed by one passage of an axle. (1)
Moisture Sensitivity Test. Also known as TSR or Modified Lottman. This test attempts to predict whether a mixture is susceptible to stripping. It compares wet strength to dry strength, and identifies adhesion and cohesion problems.
Non-wearing course is typically the bituminous mixture below the wearing course or driving surface. Non-wear mixtures include base, level and binder courses. In Superpave (Gyrarory) design, non-wearing course is defined as mixture below the top four inches of pavement. Local governments can modify the Superpave (Gyrarory) definition to define non-wear as mixture below the top three inches of pavement.
One containing less-fine aggregate in which the void spaces in the compacted aggregate are relatively large and interconnected, usually 10% more. (1)
Optimum Moisture Content
In a soil, the moisture content at which maximum density can be achieved. (2)
The lower or underlying pavement course atop the subbase or subgrade and under the top or wearing course. (1)
The entire pavement system of selected materials from subgrade to the surface. (1)
A classification system of asphalt cements based on penetration in 0.1 mm at 25°C (77°F). There are five standard penetration grades for paving: 40-50, 60-70, 85-100, 120-150, and 200-300. (1)
The consistency of a bituminous material expressed as the distance (in tenths of a millimeter) that a standard needle penetrates a sample vertically under specified conditions of loading, time and temperature. (1)
Performance Graded (PG)
Asphalt binder grade designation used in Superpave. It is based on the binder's mechanical performance at critical temperatures and aging conditions. (1)
A measure of the rate or volume of flow of water through a soil or other material including HMA.(2)
An asphalt concrete mixture that is not prepared at the paving site. Resilient Modulus: May be referred to as modulus of elasticity. It is not the same as the modulus of subgrade reaction, k although the two are related. For positive values of the resilient modulus, MR » k x 19.4. The resilient modulus is also approximately equal to 1500 times the California Bearing Ratio (CBR).
Excavated asphalt pavement that has been pulverized, usually by milling, and is used like an aggregate in the recycling of asphalt pavements. (1)
Recycled Asphalt Mix
A mixture produced after processing existing asphalt pavement materials. The recycled mix may be produced by hot or cold mixing at a plant, or by processing the materials cold and in-place. (1)
Resilient Modulus of Elasticity (MR)
A laboratory measurement of the behavior of pavement materials to characterize their stiffness and resiliency (see Soils Manual, MS-10). A confined or unconfined test specimen (core or recompacted) is repeatedly loaded and unloaded at a prescribed rate. The resilient modulus is a function of load duration, load frequency, and number of loading cycles. (2)
Resistance Value (R-value)
A test for evaluating bases, subbases, and subgrades for pavement thickness design. (1)
Fine aggregate (any fraction below a No. 8 sieve) resulting from natural disintegration and abrasion or processing of rock. (1)
Saw And Seal
Saw and seal involves sawing newly placed bituminous pavement to control thermal cracking.
A thin surface treatment used to improve the surface texture and protect an asphalt surface. The main types of seal coats are fog seals, sand seals, slurry seals, micro-surfacing, cape seals, sandwich seals and chip seals. (1)
Suitable material obtained from roadway cuts, borrow areas, or commercial sources and designated or reserved for use as foundation for the subbase, for subbase material, shoulder surfacing, or other specific purposes. (2)
An apparatus for laboratory work in which the openings in the mesh are square for separating sizes of material. (1)
A hardened material formed by curing a mechanically mixed and compacted mixture of pulverized soil, portland cement and water used as a layer in a pavement system to reinforce and protect the subgrade or subbase. (1)
Aggregate characteristics that must follow certain criteria to satisfy a Superpave mix design. Specified values are established by local agencies. They include Toughness, Soundness, and Deleterious Materials. (1)
Special directions, provisions, or requirements peculiar to the project under consideration and not otherwise thoroughly or satisfactorily detailed or set forth in the specifications. Special provisions set forth the final contractual intent in the matter involved. (2)
A layer of aggregate of planned thickness and quality placed on the existing soil as a foundation for the base. Subgrade: The portion of a roadbed surface that has been prepared as specified, upon which a subbase, base, base course, or pavement is to be constructed.
The soil prepared to support a pavement structure or a pavement system. It is the foundation of the pavement structure. (1)
Modification of roadbed soils by admixing with stabilizing or chemical agents that will increase loadbearing capacity, firmness, and resistance to weathering or displacement. (2)
Short for "SUperior PERforming Asphalt PAVEment" a performance-based system for selecting and specifying asphalt binders and for designing asphalt mixtures. (1)
Superpave® Gyratory Compactor (SGC)
A device used during Superpave® mix design or quality control activities for compacting samples of hot mix asphalt into specimens used for volumetric analysis. Continuous densification of the specimen is measured during the compaction process. (1)
Superpave® Mix Design
An asphalt mixture design system that integrates the selection of materials (asphalt, aggregate) and volumetric proportioning with the project's climate and design traffic. (1)
The initial application of asphalt material to an existing asphalt or concrete surface to provide bond between the existing surface and the new material.
Total Voids In An Asphalt Mixture
Total volume of air in the asphalt mixture.
The number of ESALs contributed by one passage of a vehicle. Truck Factors can apply to vehicles of a single type or class or to a group of vehicles of different types. (1)
A classification system of asphalt cements based on viscosity ranges at 60°C (140°F). A minimum viscosity at 135°C (275°F) is also usually specified. The purpose is to prescribe limiting values of consistency at these two temperatures. 60°C (140°F) approximates the maximum temperature of an asphalt pavement surface in service in the U.S. 135°C (275°F) approximates the mixing and laydown temperatures for hot mix asphalt pavements. (1)
A measure of a liquid's resistance to flow with respect to time. (1)
Voids in Mineral Aggregate. Measure of unabsorbed asphalt and air voids.
Voids filled with asphalt
The portion of the voids in mineral aggregate of an asphalt mixture that excludes the air voids, as well as the asphalt absorbed by the aggregate.
Wearing Course (WE)
Wearing course is typically the bituminous mixture used for the driving surface. In Superpave® (Gyratory) design, wearing course is defined as mixture within four inches of the surface. Local governments can modify the Superpave® (Gyrarory) definition to define as mixture within three inches of the surface.
Aggregate graded with relatively uniform proportions, from the maximum size down to filler. (1)
(1) Minnesota Asphalt Pavement Association, Asphalt Paving Design Guide (PDF), (cited 2004)
(2) Asphalt Institute (Internet), Asphalt Industry Glossary of Terms (PDF), 2003 (cited 2004)