Absolute viscosity
A measure of the viscosity of asphalt with respect to time, measured in poises, conducted at 60°C (140°F).

A collective term for the mineral materials such as sand, gravel and crushed stone that are used with a binding medium (such as water, bitumen, portland cement, lime, etc.) to form compound materials (such as asphalt concrete, portland cement concrete, etc.).

Sampling, testing, and the assessment of test results to determine whether or not the quality of produced material or construction is acceptable in terms of the specifications.

Alligator cracks
A series of interconnected cracks caused by fatigue failure of the HMA surface (or stabilized base) under repeated traffic loading.

API Gravity
The American Petroleum Institute (API) classifies crude oils by their API gravity. API gravity is an arbitrary expression of a material’s density at 15.5° C (60° F).

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 binder
the principal asphaltic binding agent in HMA. “Asphalt binder” includes asphalt cement as well as any material added to modify the original asphalt cement properties.

Asphalt cement
A fluxed or unfluxed asphalt specially prepared as to quality and consistency for direct use in the manufacture of bituminous pavements, and having a penetration at 25° C (77° F) of between 5 and 300, under a load of 100 g applied for 5 s.

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

Base course
The portion of a pavement structure immediately beneath the surface course. Its major function is structural support and usually consists of aggregate and can be either stabilized or unstabilized.

Batch plant
A manufacturing facility for producing HMA. They manufacture HMA in batches rather than continuously.

A class of black or dark-colored (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, of which asphalts, tars, pitches, and asphaltenes are typical.

A film of asphalt binder on the pavement surface caused by the upward migration of asphalt binder in an HMA pavement resulting in the formation of asphalt film on the surface. Same as flushing.

Break and seat
A process used to prevent joint reflective cracking in an HMA overlay over old PCC pavement. It involves breaking up the underlying rigid pavement into relatively small pieces (on the order of about 0.3 m2 to 0.6 m2 (1 ft2 to 2 ft2) by repeatedly dropping a large weight. The pieces are then seated by 2 to 3 passes of a large rubber tired roller.

The phenomenon when asphalt and water separate in an asphalt emulsion beginning the curing process.

California Bearing Ratio. A strength test typically used on unconfined granular material.

Cessation temperature
As HMA cools, the asphalt binder eventually becomes viscous enough to effectively prevent any further reduction in air voids regardless of the applied compactive effort. As a rule-of-thumb the temperature at which this occurs, commonly referred to as cessation temperature, is about 79oC (175°F) for dense-graded HMA.

Hairline surface cracks in an HMA mat caused by steel wheel rollers.

Cold In-Place Recycling. A general term for processes using grinding machines to recycle pavement into base material for new paving. CIPR often uses additives such as emulsions or foamed asphalt for stabilization.

Compactive effort
The combined effect of (1) applying weight to an HMA surface and compressing the material underneath the ground contact area and (2) creating a shear stress between the compressed material underneath the ground contact area and the adjacent uncompressed material.

Consensus requirements (properties)
A set of aggregate properties including: minimum angularity, flat or elongated particle and clay content requirements. These requirements came about because SHRP did not specifically address aggregate properties and it was thought that there needed to be some aggregate properties guidance associated with the Superpave mix design method. Therefore, an expert group on aggregate properties was convened and arrived at a consensus on several aggregate property requirements.

A pavement surface distortion perpendicular to the traffic direction caused by plastic movement and typified by ripples across a pavement surface. Usually caused by vehicle starting and stopping.

Crude Oil
Unrefined petroleum.

Dense-graded mix
Refers to an HMA mix design using an aggregate gradation that is near the FHWA’s 0.45 power curve for maximum density. These are the most common HMA mix designs in the U.S.

Drum plant
A manufacturing facility for producing HMA. They manufacture HMA continuously rather than in batches.

A measure of how asphalt binder physical properties change with age (sometimes called age hardening). In general, as an asphalt binder ages, its viscosity increases and it becomes more stiff and brittle.

Elastic modulus
The relationship between stress and strain within a material’s elastic range. Thus, the “flexibility” of any object depends on its elastic modulus and geometric shape; however, it is important to note that strength (stress needed to break something) is not the same thing as stiffness (as measured by elastic modulus).

A suspension of small asphalt cement globules in water. The suspension is assisted by an emulsifying agent.

Emulsifying agent
A substance used in asphalt emulsions to assist the formation of small asphalt cement globules in water by imparting an electrical charge to the surface of the asphalt cement globules so that they do not coalesce.

Equivalent Single Axle Load. Based on the results from the AASHO Road Test, the most common approach to determining traffic loading is to convert wheel loads of various magnitudes and repetitions to an equivalent number of “standard” or “equivalent” loads. The most commonly used equivalent load in the U.S. is the 80 kN (18,000 lbs.) equivalent single axle load.

Fatigue cracking
Cracks caused by fatigue failure of an HMA surface (or stabilized base) under repeated traffic loading.

Full-depth CIPR. FDR can be used to depths of 30 mm (12 inches) or more but the most typical applications involve depths of between 150 and 225 mm (6 and 9 inches).

Federal Highway Administration. Founded on 3 October 1893 as the Office of Road Inquiry, a small office of the U.S. Department of Agriculture. The Office of Road Inquiry was created to gather and disseminate information on road building. The office grew from just two employees to about 3,500 and its annual budget grew from $10,000 to more than $26 billion. The office is now known as the Federal Highway Administration (FHWA) and is part of the U.S. Department of Transportation, which was formed in 1967. (from FHWA, http://www.fhwa.dot.gov/highwayhistory/history_fhwa.cfm).

Flexible pavement
Pavements that are surfaced with bituminous (or asphalt) materials in the surface course. These can be either in the form of pavement surfaces such as a bituminous surface course (BST) generally found on lower volume (or lower traffic) roads, or hot mix asphalt (HMA) surfaces generally used on higher volume roads. These types of pavements are called “flexible” since the total pavement structure “bends” or “deflects” due to traffic loads.

A film of asphalt binder on the pavement surface caused by the upward migration of asphalt binder in an HMA pavement resulting in the formation of asphalt film on the surface. Same as bleeding.

A bituminous material, generally liquid, used for softening other bituminous materials.

Fog seal
A light application of a slow-setting asphalt emulsion to the surface of an aged (oxidized) pavement surface.

Full-depth asphalt
An HMA pavement structure using HMA products for all components. The base material and surface courses are made of HMA instead of aggregate or other material.

Falling Weight Deflectometer. The FWD is an impact load device used to deliver a transient impulse load to the pavement surface and measure the resultant pavement response (it’s deflection) by a series of sensors.

Fabric-like materials used in the paving process. Geotextiles are manufactured for specific uses and performance characteristics. Some uses include stabilization of base material to prevent migration into sub-grades, retarding of reflective cracking in asphalt overlays, and serving as a moisture barrier between pavement layers (NPCA).

Gravel borrow
Generally “gravel borrow” refers to high quality granular fill. This granular fill may contain a substantial amount of soil but it is generally devoid of most clays/silts and other deleterious material.

Hot In-Place Recycling. A pavement recycling method that heats and rejuvenates an existing pavement surface (typically using propane radiant heaters and a rejuvenating agent) in place then mixes and levels the recycled mix using a standard auger system.

Hot Mix Asphalt. A high quality, thoroughly controlled hot mixture of asphalt binder and aggregate that can be compacted into a uniform dense mass.

Hot Mix Asphalt Concrete. Another term for HMA.

Ice lens
Subterranean ice crystals that form along the plane of freezing temperature. Water migrates up from below (where the temperature is above freezing) then freezes once it reaches the freezing depth in a soil forming an ice lens.

Independent assurance
A management tool that requires a third party, not directly responsible for process control or acceptance, to provide an independent assessment of the product and/or the reliability of test results obtained from process control and acceptance testing. The results of independent assurance tests are not to be used as a basis of product acceptance.

In place, in it’s original location.

Refers to properties that are the same regardless of the direction that is measured. Properties that are the same everywhere.

Job-mix formula. A recommended/specified mixture of aggregate and asphalt binder.

The portion of the HMA paving process where the HMA is actually placed or “laid down” by the paving machine.

Load Equivalency Factor. The output from the ESAL equation. This factor relates various axle load combinations to the standard 18,000 lb. single axle load.

Leveling course
A first lift applied to an existing pavement used to fill in ruts and make up elevation differences.

A layer or course of paving material.

Linear Elastic
A material property meaning that an object or material will return to or is capable of returning to an initial form or state after deformation in a linear manner (e.g. a plot of a linear elastic material would show a straight line). Almost no material is completely linearly elastic but many materials are linearly elastic over a certain range of stress/strain.

Liquid limit
The water content above which a soil behaves as a viscous liquid (i.e. its shearing strength is negligible).

Type of early bituminous pavement named after its inventor, a Scotsman named John McAdam (1756 – 1836). McAdam (sometimes spelled “Macadam”) pavements used smaller angular aggregate over larger angular aggregate over a well-compacted, sloped subgrade.

non-polar or relatively low-polarity molecules within asphalt cement.

A term used to describe the fresh asphalt surface behind the paving machine. Most commonly used to refer to the asphalt during the laydown and compaction phase of construction.

Mat tearing
A term used to describe the pulling of the HMA under the screed of the paver. Generally results in coarse-textured streaks behind the paver.

An advanced form of slurry seal that uses the same basic ingredients (emulsified asphalt, water, fine aggregate and mineral filler) and combines them with advanced polymer additives to produce a more capable end product.

Mineral filler
Defined by the Asphalt Institute as a finely divided mineral product at least 65 percent of which will pass through a No. 200 sieve.  Pulverized limestone is the most commonly manufactured mineral filler, although other stone dust, silica, hydrated lime, portland cement and certain natural deposits of finely divided mineral matter are also used (Asphalt Institute, 1962).

Material Transfer Vehicle. Used to assist the paver in accepting HMA. Most pavers are equipped to receive HMA directly, however in certain situations it can be necessary or advantageous to use an MTV. Paving using bottom dump trucks and windrows requires a windrow elevator MTV while other MTVs are used to provide additional surge volume, which is advantageous because it allows the paver to operate continuously without stopping, minimizes truck waiting time at the paving site and may minimize segregation and temperature differentials.

National Asphalt Pavement Association. NAPA supports an active research program designed to improve the quality of HMA pavements and paving techniques used in the construction of roads, streets, highways, parking lots, airports, and environmental and recreational facilities. The Association provides technical, educational, and marketing materials and information to its Members, as well as product information to users and specifiers of paving materials. The Association, whose members number more than 1,100 companies, was founded in 1955. http://www.hotmix.org.

National Center for Asphalt Technology. NCAT was established at Auburn University in 1986 with an endowment set up by the NAPA Research and Education Foundation. Its mission is to improve HMA performance through research, education, and information services.  http://www.eng.auburn.edu/center/ncat.

Not frost susceptible.

Optimum moisture content
In a soil, the moisture content at which maximum density can be achieved.

Portland cement concrete.

A property describing the degree to which a material can be permeated or penetrated, especially by liquids or gases.

Perpetual pavement
Long-lasting HMA pavement.

Plasticity index (PI)
the numerical difference between the Liquid Limit and the Plastic Limit of a soil.

Plastic limit
The water content below which a soil ceases to behave as a plastic medium and beings to exhibit the properties of a semisolid.

Polar molecule
A molecule having a pair of electric charges or magnetic poles, of opposite sign or polarity, separated by a small distance. This is usually determined by the arrangement of atoms and relative electron location probabilities of the bonded molecule.

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

Prime coat
An application of asphalt primer to an absorbent surface. Often 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.

Present Serviceability Index. A pavement condition index.

Present Serviceability Rating. A definition of pavement serviceability based on individual observation.

Pavement deflection (usually repeated) under traffic that sometimes results in the discharge of water and subgrade soils along joints, cracks and pavement edges.

Quality assurance
All those planned and systematic actions necessary to provide confidence that a product or facility will perform satisfactorily in service. Quality assurance addresses the overall problem of obtaining the quality of a service, product, or facility in the most efficient, economical, and satisfactory manner possible. Within this broad context, quality assurance involves continued evaluation of the activities of planning, design, development of plans and specifications, advertising and awarding of contracts, construction, and maintenance, and the interactions of these activities. Note that this definition is not always consistent with other quality assurance definitions.

Quality control
Those quality assurance actions and considerations necessary to assess production and construction processes so as to control the level of quality being produced in the end product. This concept of quality control includes sampling and testing to monitor the process but usually does not include acceptance sampling and testing. Also called process control.

Reclaimed Asphalt Pavement. RAP is typically generated by (1) milling machines in rehabilitation projects or (2) a special crushing plant used to break down large pieces of excavated HMA pavement.  In Washington State and across the country, RAP has been widely used in a “closed loop” recycling process for over two decades, making asphalt pavements the most widely recycled product in America.  Asphalt pavements are 100% recyclable.

Recycled Asphalt Shingles.  RAS can be successfully used as a supplement asphalt binder source for HMA pavements in small proportions (typically 3% by weight or less).  Roofing shingles, recycled either from “tear offs” or manufacturer waste, is ground into a fine graded mixture and added to the HMA manufacturing process.  This process reclaims the valuable asphalt in the shingles and keeps the shingles from being wasted in a landfill.  King County has been a leader in promoting the use of RAS in Washington State and readily accepts RAS modified HMA in its roadway and facility pavements.

Reflective cracking
Cracks in an HMA overlay caused by cracks in the existing pavement “reflecting” up through the overlay.

In petroleum refining, they are the left-overs from the refining process.

Resilient Modulus
An estimate of a material’s elastic modulus based on stress and strain measurements from rapidly applied loads – like those that pavement materials experience from wheel loads.

Restricted zone
A particular area of the 0.45 power gradation graph associated with Superpave mix designs. Initially, it was thought that mixes closely following the 0.45 power maximum density line could sometimes have unacceptably low VMA. Therefore, Superpave introduced a restricted zone through which a typical gradation should not pass. Recent studies have shown the restricted zone to be unecessary and it will be removed.

Recycled Hot Mix.

Rice density
The theoretical maximum density of an HMA if it contained zero air voids.

Road reclaimer
A self-propelled machine having a transverse cutting and mixing head inside of a closed chamber for the pulverization and mixing of existing pavement materials with asphalt emulsion.

Reducing a material or structure to rubble. Regarding pavements, rubblization usually refers to reducing an existing rigid pavement to rubble in preparation for an HMA overlay. This helps prevent reflective cracking in the new overlay.

Surface depression in the wheelpath of a pavement.

The part of a paving machine that spreads, smoothes, and provides initial compaction of the HMA.

Seal coat
A collective term for several different kinds of thin surface treatments used to improve the surface texture and protect an HMA surface. Seal coats include fog seals, slurry seals, micro-surfacing, and BSTs.

Regarding HMA, the broad definition 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 pavement distress(es).” Typically though, “segregation” refers to aggregate segregation, which is “the non-uniform distribution of coarse and fine aggregate components within the asphalt mixture.”

State Highway Association.

Shear Flow
To undergo plastic deformation and movement without cracking or breaking.

Sheepsfoot Roller
Steel wheel roller with large protrusions on the drum used for soil compaction.

A form of plastic movement typified by an abrupt wave across the pavement surface. The distortion is perpendicular to the traffic direction. Usually occurs at points where HMA abuts a rigid object.

Strategic Highway Research Plan.

Skid resistance
The ability of a pavement to offer resistance to slipping or skidding.

Slurry Seal
A homogenous mixture of emulsified asphalt, water, well-graded fine aggregate and mineral filler. Slurry seals are used to fill existing pavement surface defects as either a prepatory maintenance or as a wearing course.

Term often used to describe an aggregate’s weathering resistance characteristics (e.g. wetting/drying, freezing/thawing).

A term often used to describe an HMA’s ability to resist deformation under loading.

the portion of the pavement structure between the subgrade and the base course. A subbase course is not always needed or used.

The material upon which the pavement structure is built. It can either be in-situ material or structural fill material.

Superior Performing Asphalt Pavements. An overarching term for the results of the asphalt research portion of the 1987 – 1993 Strategic Highway Research Program (SHRP). Superpave consists of (1) an asphalt binder specification, (2) an HMA mix design method and (3) HMA tests and performance prediction models. Each one of these components is referred to by the term “Superpave”.

Surface course
The top pavement layer and the layer that comes in contact with traffic.

Tack coat
Asphalt oil, usually an emulsion, applied to existing pavement during repairs or overlay paving to create a bond between the old and new asphalt (NPCA).

Test strip
A small section of mat laid out at the beginning of a project with the purpose of determining the best roller type, sequence, number of passes and rolling pattern to use.

Thermal cracking
Cracking caused by shrinkage of the pavement surface due to low temperatures.

Theoretical maximum density. The theoretical maximum density of an HMA if it contained zero air voids.

The volume of intergranular void space between the aggregate particles of a compacted paving mixture that includes the air voids and the effective asphalt content, expressed as a percent of the total volume of the specimen.

Washington Asphalt Pavement Association.  Formed in 1954,  the association represents nearly all hot mix asphalt producers in the State as well as other related industries.  The purpose of this association is to promote improved communication and understanding within the entire hot mix asphalt paving industry; influence fair and equitable design, specifications and inspection; protect the doctrine of free enterprise and competition; stimulate and encourage extensive research relative to the manufacture and use of hot mix asphalt pavement; educate within the industry for higher standards, lawful trade practices and ethical conduct; and act and function as an educational association on behalf of the asphalt paving industry.  Formerly known as the Asphalt Paving Association of Washington (APAW).  The association updated its name in November 2002 to better conform with its sister associations in other states and to avoid confusion with the American Public Works Association (APWA).

Wearing course
The pavement layer in direct contact with traffic loads. Sometimes “wearing course” is used interchangeably with “surface course” and sometimes it is used to mean the top portion of the surface course. It is meant to take the brunt of traffic wear and can be removed and replaced as it becomes worn.

That portion of a pavement that is contacted by the wheels/tires of vehicles in a typical traffic stream. There are generally two wheelpaths per lane.

Regarding HMA, a term that refers to an HMA’s ability to be placed and compacted. Workable mixes are easy to place and compact and are generally more viscous than mixes with poor workability.