Absolute Viscosity

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.


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.

Aggregate Spreaders

Machines used for spreading aggregate evenly at a uniform rate on a surface.

Aggregate Storage Bins

Bins that store the necessary aggregate sizes and feed them to the dryer in substantially the same proportions as are required in the finished mix.

Aggregate Trucks

Trucks equipped with hydraulic lifts to dump the aggregate into the spreader or storage area.

Air Voids

Internal spaces in a compacted mix surrounded by asphalt-coated particles, expressed as a percentage by volume of the total compacted mix.

Alligator Cracks

Interconnected cracks forming a series of small blocks resembling an alligator's skin or chicken-wire, and caused by excessive deflection of the surface over unstable subgrade or lower courses of the pavement.

Asphalt Binder (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.

Asphalt Binder

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.

Asphalt Concrete

A mixture of asphalt binder and aggregate thoroughly mixed and compacted into a mass.

Asphalt Distributor

A truck or a trailer having an insulated tank, heating system and distribution system. The distributor applies asphalt to a surface at a uniform rate.

Asphalt Emulsion

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).

Asphalt Leveling Course (Leveling Binder)

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.

Asphalt Pavements

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.

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.

Asphalt Primer

Low viscosity asphalt (highly liquid) that penetrates into a non- bituminous surface upon application.

Asphalt Tack Coat

A relatively thin application of asphalt binder applied to an existing asphalt concrete or PCC surface at a prescribed rate. Asphalt emulsion diluted with water is the preferred type. It is used to form a bond between an existing surface and the overlying course.


The high molecular weight hydrocarbon fraction precipitated from asphalt by a designated paraffinic naphtha solvent at a specified solvent-asphalt ratio.

Automatic Cycling Control

A control system in which the opening and closing of the weigh hopper discharge gate, the bituminous discharge valve, and the pugmill discharge gate are actuated by means of self-acting mechanical or electrical machinery without any intermediate manual control. The system includes preset timing devices to control the desired periods of dry and wet mixing cycles.

Automatic Dryer Control

A system that automatically maintains the temperature of aggregates discharged from the dryer within a preset range.

Automatic Proportioning Control

A system in which proportions of the aggregate and asphalt fractions are controlled by means of gates or valves, which are opened and closed by means of self-acting mechanical or electronic machinery without any intermediate manual control.


An analytical technique used to determine the equivalent elastic moduli of pavement layers corresponding to the measured load and deflections. In the iterative method, layer moduli are selected and adjusted until the difference between the calculated and measured deflections are within selected tolerances, or the maximum number of iterations has been reached.

Bank Gravel

Gravel found in natural deposits, usually intermixed with fine material such as sand or clay or a combination thereof; includes gravelly clay, gravelly sand, clayey gravel, and sandy gravel (the names indicate the relative proportion of the materials in the mixture).

Base Course

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.

Batch Plant

A manufacturing facility for producing asphalt paving mixtures that proportions blending.  They manufacture asphalt in batches rather than continuously and are more suited for small manufacturing runs and (frequent) changes in mixture types.

Binder Course

The hot mix asphalt course immediately below the surface course, generally consisting of larger aggregates and less asphalt (by weight) than the surface.


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.

Blast-Furnace Slag

The nonmetallic product, consisting essentially of silicates and alumina-silicates of lime and of other bases, that is developed simultaneously with iron in a blast furnace.

Bleeding or Flushing Asphalt

The upward migration of asphalt binder in an asphalt pavement resulting in the formation of asphalt film on the surface.

California Bearing Ratio (CBR)

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.

Cape Seal

A surface treatment where a chip seal is followed by the application of either slurry seal or micro-surfacing.

Channels (Ruts)

Channeled depressions that sometimes develop in the wheel paths of an asphalt pavement.

Coal Tar

A dark brown to black cementitious material produced by the destructive distillation of bituminous coal.

Coarse Aggregate

Aggregate retained on the 2.36 mm (No. 8) sieve.

Coarse-Graded Aggregate

One having a continuous grading in sizes of particles from coarse through fine with a predominance of coarse sizes.


The act of compressing a given volume of material into a smaller volume.

Consensus Properties

Aggregate characteristics that must follow certain criteria to satisfy a Superpave mix design. Specified test values for these properties are not source specific but widely agreed upon. They include Coarse Aggregate Angularity, Fine Aggregate Angularity, Flat or Elongated Particles, and Clay Content.


The degree of fluidity of asphalt cement at any particular temperature. The consistency of asphalt cement varies with its temperature; therefore, it is necessary to use a common or standard temperature when comparing the consistency of one asphalt cement with another.

Corrugations (Washboarding) and Shoving

A type of pavement distortion. Corrugation is a form of plastic deformation typified by ripples across the pavement surface. These distortions usually occur at points where traffic starts and stops, on hills where vehicles brake on the downgrade, on sharp curves, or where vehicles hit a bump and bounce up and down. They occur in asphalt layers that lack stability.


An approximately vertical random cleavage of the pavement caused by traffic loading, thermal stresses and/or aging of the binder.

Crack and Seat

A fractured slab technique used in the rehabilitation of PCC pavements that minimizes slab action in a jointed concrete pavement (JCP) by fracturing the PCC layer into smaller segments. This reduction in slab length minimizes reflective cracking in new HMA overlays.

Crack-Relief Layer

A large stone, open graded asphalt mixture placed over a distressed pavement that minimizes reflective cracking by absorbing the energy produced by movement in the underlying pavement.


The total unscreened product of a stone crusher.


The development of the mechanical properties of the asphalt binder. This occurs after the emulsion has broken and the emulsion particles coalesce and bond to the aggregate.

Cutback Asphalt

Asphalt cement that has been liquefied by blending with petroleum solvents (diluents). Upon exposure to atmospheric conditions the diluents evaporate, leaving the asphalt cement to perform its function.


A load-induced, downward movement of a pavement section.

Deflection Basin

The idealized shape of the deformed pavement surface as a result of a cyclic or impact load as depicted from the peak measurements of five or more deflection sensors.

Rebound Deflection

The amount of surface rebound when a load is removed.

Representative Rebound Deflection

The mean value of measured rebound deflections in a test section, plus two standard deviations, adjusted for temperature and most critical period of the year for pavement performance.

Residual Deflection

The difference between original and final elevations of the pavement surface resulting from the application to, and removal of, one or more loads from the surface.

Deflection Sensor

The term that shall be used to refer to the electronic device(s) capable of measuring the vertical movement of the pavement; and, mounted in such a manner as to minimize angular rotation with respect to its measuring plane at the expected movement. Sensor types include seismometers, velocity transducers, and accelerometers.

Delivery Tolerances

Permissible variations from the exact desired proportions of aggregate and bituminous material as manufactured by an asphalt plant.

Dense-Graded Aggregate

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%.


The act of increasing the density of a mixture during the compaction process.

Design ESAL

The total number of equivalent 80-kN (18,000-lb.), single- axle load applications (equivalent single axle loads) expected throughout the design period.

Design Lane

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.

Design Period

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.

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.


The breaking up of a pavement into small, loose fragments caused by traffic or weathering (e.g. raveling).


Any change of a pavement surface from its original shape.

Drum Mix Plant

A manufacturing facility for producing asphalt paving mixtures that proportions the aggregate, then dries and coats the aggregate with a proportional amount of asphalt in the same drum. Variations of this type of plant use several types of drum modifications, separate (and smaller) mixing drums, and coating units (coater) to accomplish the mixing process.  They are more suited for long runs of the same product.


An apparatus that will dry the aggregates and heat them to the specified temperatures.


The ability of a substance to be drawn out or stretched thin. While ductility is considered and important characteristic of asphalt cements in many applications, the presence or absence of ductility is usually considered more significant than the actual degree of ductility.


The property of an asphalt pavement that represents its ability to resist disintegration by weathering and traffic.

Edge Joint Cracks

The separation of the joint between the pavement and the shoulder, commonly caused by the alternate wetting and drying beneath the shoulder surface. Other causes are shoulder settlement, mix shrinkage, and trucks straddling the joint.

Effective Thickness

The ratio of the thickness of an existing pavement material compared to the equivalent thickness of a new HMA layer.

Emulsifying Agent or Emulsifier

The chemical added to the water and asphalt that keeps the asphalt in stable suspension in the water. The emulsifier determines the charge of the emulsion and controls the breaking rate.

ESAL (equivalent single axle loads)

The effect on pavement performance of any combination of axle loads of varying magnitude equated to the number of 80-kN (18,000-lb.) single-axle loads that are required to produce an equivalent effect.

Fatigue Resistance

The ability of asphalt pavement to resist crack initiation caused by repeated flexing.


A difference in elevation of two slabs at a joint or crack.

Fine Aggregate

Aggregate passing the 2.36 mm (No. 8) sieve.

Fine-Graded Aggregate

One having a continuous grading in sizes of particles from coarse through fine with a predominance of fine sizes.


The ability of an asphalt pavement structure to conform to settlement of the foundation. Generally, flexibility of the asphalt paving mixture is enhanced by high asphalt content.

Fog Seal

A light application of diluted asphalt emulsion. It is used to renew old asphalt surfaces, seal small cracks and surface voids, and inhibit raveling.

Fractured Slab Techniques

Processes used to rehabilitate PCC pavements by eliminating slab action through the reduction of slab size (crack/break and seat) or the pulverization of the PCC slab (rubblization) into essentially a granular base.

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.

Heavy Trucks

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.

Hot Aggregate Storage Bins

Bins that store heated and fractionated aggregates prior to their final proportioning into the mixer.

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.

Hot Mix Asphalt (HMA) Overlay

One or more courses of HMA over an existing pavement.


The resistance an asphalt pavement has to the passage of air and water into or through the pavement.

Kinematic Viscosity

A measure of the viscosity of asphalt, measured in centistokes, conducted at a temperature of 275°F (135°C).

Lane Joint Cracks

Longitudinal separations along the seam between two paving lanes.


A layer or course of paving material applied to a base or a previous layer.

Lime Treated Subgrade

A subgrade preparation technique in which the subgrade soil and added lime are mechanically mixed and compacted to produce a higher modulus base material than the in-situ material.

Lime-Fly Ash Base

A road base material consisting of a blend of mineral aggregate, lime, fly ash, and water, which when combined in proper proportions and compacted produces a dense mass of increased strength.

Longitudinal Crack

A vertical crack in the pavement that follows a course approximately parallel to the centerline.

Mechanical Spreaders

Spreader boxes that are mounted on wheels. The spreaders are attached to and pushed by dump trucks (HMA boxes are pulled and chip spreaders are pushed).

Medium-Curing (MC) Asphalt

Cutback asphalt composed of asphalt cement and a diluent of medium volatility.


The square opening of a sieve.

Milling Machine

A self-propelled unit having a cutting head equipped with carbide- tipped tools for the pulverization and removal of layers of asphalt materials from pavements.

Mineral Dust

The portion of the fine aggregate passing the No. 200 (0.075 mm) sieve.

Mineral Filler

A finely divided mineral product, at least 70 percent of which will pass a No. 200 (0.075 mm) sieve. Pulverized limestone is the most commonly manufactured filler, although other stone dust, hydrated lime, portland cement, and certain natural deposits of finely divided mineral matter are also used.

Open-Graded Aggregate

One containing less-fine aggregate in which the void spaces in the compacted aggregate are relatively large and interconnected, usually 10% more.

Open-Graded Asphalt Friction Course

A pavement surface course that consists of a high-void, asphalt plant mix that permits rapid drainage of rainwater through the course and out the shoulder. The mixture is characterized by a large percentage of one-sized coarse aggregate. This course prevents tires from hydroplaning and provides a skid-resistant pavement surface with significant noise reduction.


The SI unit for viscosity. 1 Pascal-second equals 10 poises.

Pavement Base

The lower or underlying pavement course atop the subbase or subgrade and under the top or wearing course.

Pavement Structure

The entire pavement system of selected materials from subgrade to the surface.

Penetration Grading

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.


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.

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.

Planned Stage Construction

A construction process where stages of the project are performed sequentially according to design and a predetermined time schedule.

Plant Screens

Screens located between the dryer and hot bins, which separate heated aggregates into proper hot bin sizes.

Pneumatic-Tire Roller

A compactor with a number of tires spaced so their tracks overlap delivering a kneading type of compaction.


A centimeter-gram-second  unit of absolute viscosity equal to the viscosity of a fluid in which a value of stress one dyne per square centimeter is required to maintain a difference of velocity of one centimeter per second between two parallel planes in the fluid that lie in the direction of flow and are separated by a distance of one centimeter.

Polished Aggregate

Aggregate particles in a pavement surface that have been worn smooth by traffic.

Polymer-Modified Asphalt (PMA) Binder

Conventional asphalt cement to which one or more polymer compounds (typically SBS or SBR) have been added to improve resistance to deformation at high pavement temperatures and often cracking resistance at low temperatures.


Bowl-shaped openings in the pavement resulting from localized disintegration.

Power Sweeper

A power operated rotary broom used to clean loose material from the pavement surface.


Slab deflection under passing loads sometimes resulting in the discharge of water and subgrade soils along joints, cracks and pavement edges.

Rapid-Curing (RC) Asphalt

Cutback asphalt composed of asphalt cement and a naphtha or gasoline-type diluent of high volatility.


The progressive separation of aggregate particles in a pavement from the surface downward or from the edges inward.

Reclaimed Asphalt Pavement (RAP)

Excavated asphalt pavement that has been pulverized, usually by milling, and is used like an aggregate in the recycling of asphalt pavements.

Reflection Cracks

Cracks in asphalt overlays (usually over deteriorated PCC pavements) that reflect the crack pattern in the pavement structure below it.


The asphalt binder that remains from an asphalt emulsion after the emulsifying agent has broken and cured, or the remains of a cutback after the volatiles have cured.

Resilient Modulus of Elasticity (MR)

A laboratory measurement of the behavior of pavement materials to characterize their stiffness and resiliency (see Asphalt Institute 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.

Resistance Value (R-value)

A test for evaluating bases, subbases, and subgrades for pavement thickness design.

Road Oil

Asphalt cement and oils of low volatility, usually similar to one of the slow-curing (SC) grades.


All facilities on which motor vehicles are intended to travel such as secondary roads, interstate highways, streets and parking lots.


The pulverization of a portland cement concrete pavement into smaller particles, reducing the existing pavement layer to a sound, structural base that will be compatible to an asphalt overlay.


Fine aggregate (any fraction below a No. 8 sieve) resulting from natural disintegration and abrasion or processing of rock.

Sandy Soil

A material consisting essentially of fine aggregate particles smaller than 2.36 mm (No. 8) sieve and usually containing material passing a 75 µm (No. 200) sieve. This material usually exhibits some plasticity characteristics.

Saw-Cut and Seal

A method of controlling reflective cracking in HMA overlays that involves constructing joints in the new overlay exactly over the joints in the existing pavement.


The peeling away or disintegrating of the surface of portland cement concrete.

Self-Propelled Spreaders

Spreaders having their own power units and two hoppers. The spreader pulls the truck as it dumps its load into the receiving hopper. Conveyor belts move the aggregate forward to the spreading hopper.

Sheet Asphalt

A hot mixture of asphalt binder with clean, angular, graded sand and mineral filler. Its use is ordinarily confined to reservoir liners and landfill caps; usually laid on an intermediate or leveling course.


A form of plastic movement resulting in localized bulging of the pavement.

Shrinkage Cracks

Interconnected cracks forming a series of large blocks, usually with sharp corners or angles.


An apparatus for laboratory work in which the openings in the mesh are square for separating sizes of material.

Skid Resistance

The ability of a paved surface, particularly when wet, to offer resistance to slipping or skidding. Proper asphalt content and aggregate with a rough surface texture are the greatest contributors. The aggregate must not only have a rough surface texture, but also resist polishing.

Slippage Cracks

Crescent-shaped cracks resulting from traffic-induced horizontal forces that are open in the direction of the thrust of wheels on the pavement surface. They result when severe or repeated shear stresses are applied to the surface and there is a lack of bond between the surface layer and the course beneath.

Slow-Curing  (SC)

Cutback asphalt composed of asphalt cement and oils of low Asphalt volatility.

Soil/Cement  Base

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.


A measure of the purity of asphalt cement. The ability of the portion of the asphalt cement that is soluble to be dissolved in a specified solvent.


The breaking or chipping of a PCC pavement at joints, cracks, or edges, usually resulting in fragments with featheredges.


The ability of an asphalt paving mixture to resist deformation from imposed loads. Stability is dependent upon both internal friction and cohesion.

Standard Deviation

The root-mean-square of the deviations about the arithmetic mean of a set of values.

Stationary Plants

Asphalt plants that are so constructed that moving them is not considered economically feasible.

Steel-Wheel Static Rollers

Tandem or three-wheel rollers with cylindrical steel rolls that apply their weight directly to the pavement.

Steel-Wheel Vibratory Rollers

A compactor having single or double cylindrical steel rolls that apply compactive effort with weight and vibration. The amount of compactive force is adjusted by changing the frequency and amplitude of vibration.


A unit of kinematic viscosity equal to the viscosity of a fluid in poises divided by the density of the fluid in grams per cubic centimeter.

Structural Overlay

A HMA overlay constructed for the purpose of increasing the structural value and ride quality of the pavement system.


The course in the asphalt pavement structure immediately below the base course. If the subgrade soil has adequate support, it may serve as the subbase.

Subgrade Resilient Modulus

The modulus of the subgrade determined by repeated load, triaxial compression tests on soil samples. It is the ratio of the amplitude of the accepted axial stress to the amplitude of the resultant recoverable axial strain, generally designated by the symbol MR.

Subgrade, Improved

Subgrade that has been improved as a working platform by: 1) the incorporation of granular materials or stabilizers such as asphalt, lime, or portland cement into the subgrade soil; 2) any course or courses of select or improved material placed on the subgrade soil below the pavement structure.


The soil prepared to support a pavement structure or a pavement system. It is the foundation of the pavement structure.

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.

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.


Short for "Superior Performing Asphalt Pavement" a performance-based system for selecting and specifying asphalt binders and for designing asphalt mixtures.

Transverse Crack

A crack that follows a course approximately at right angles to the centerline.

Travel Plants

Self-propelled pugmill plants that proportion and mix aggregates and asphalt as they move along the road. There are three general types of travel plants:

  1. One that moves through a prepared aggregate windrow on the roadbed, adds and mixes the asphalt as it goes, and rear discharges a mixed windrow ready for aeration and spreading.
  2. One that receives aggregate into its hopper from haul trucks, adds and mixes asphalt, and spreads the mix to the rear as it moves along the roadbed.
  3. Batch mixing units, such as slurry machines, that haul materials to the site and then mix and apply the materials.

Truck Factor

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.

Viscosity Grading

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 United States. 135°C (275°F) approximates the mixing and laydown temperatures for hot mix asphalt pavements.


A measure of a liquid's resistance to flow with respect to time.

Well-Graded Aggregate

Aggregate graded with relatively uniform proportions, from the maximum size down to filler.

Wet Mixing Period

The interval of time between the beginning of application of asphalt material into a pugmill and the opening of the discharge gate.


The ease with which paving mixtures may be placed and compacted.