American Association of State Highway and Transportation Officials

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

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.

American Concrete Institute. A nonprofit scientific and educational society, organized in 1904, to represent the user interest in the concrete field. ACI defines “user” as “the public agency, engineer, architect, owner, contractor, educator, or other specialist interested in the design, construction or maintenance of concrete structures.” ACI’s purpose is “to provide a comradeship in finding the best ways to do concrete work of all kinds and in spreading that knowledge.” (from the ACI website)

American Concrete Pavement Association. A national association representing concrete pavement contractors, cement companies, equipment and material manufacturers and suppliers. It is organized to address common needs, solve common problems, and accomplish goals related to research, market development, local promotion, design, construction and best practices of PCC pavements.

The ingredients in PCC other than aggregate, portland cement and water. Typically, an admixture is added to alter a specific PCC property such as workability, setting time, strength or durability.

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.).

Aggregate blending
Combining multiple aggregate sources to produce a desired set of properties. Usually aggregate blending is done to improve or change gradation.

Aggregate interlock
The mechanical locking which forms between the fractured surfaces along the crack below the joint saw cut (from the American Concrete Pavement Association).

The process of providing gentle motion in mixed concrete just sufficient to prevent segregation or loss of plasticity.

Alkali-aggregate reaction
The expansive reaction that takes place in PCC between alkali (contained in the cement paste) and elements within an aggregate. The most common is an alkali-silica reaction. This reaction, which occurs to some extent in most PCC, can result in map or pattern cracking, surface popouts and spalling.

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

Analysis period
The period of time over which a life-cycle cost analysis is performed.

Asphalt Pavement Alliance. A coalition of the Asphalt Institute, the National Asphalt Pavement Association, and the State Asphalt Pavement Associations. The Asphalt Pavement Alliance’s mission is to further the use and quality of Hot Mix Asphalt pavements through research, technology transfer, engineering, education and innovation.

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).

Acceptable Quality Level. The minimum level of actual quality at which the material or construction can be considered fully acceptable.

AREA Parameter (AREA Value)
Represents the normalized area of a vertical slice taken through a deflection basin between the center of the test load and 914 mm (3 feet) away from the test load. Has length dimensions.

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.

Asphalt Institute
A U.S.-based association of international petroleum asphalt/bitumen producers, manufacturers, and affiliated business. Its mission is to promote the use, benefits, and quality performance of petroleum asphalt, through environmental, marketing, research, engineering and technical development, and through the resolution of issues affecting the industry.


A mechanistic evaluation of pavement surface deflection basins generated by various pavement deflection devices. Backcalculation takes a measured surface deflection and attempts to match it (to within some tolerable error) with a calculated surface deflection generated from an identical pavement structure using assumed layer stiffnesses (moduli).

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 or PCC that makes the product 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.

In HMA “bleeding” is a film of asphalt binder on the pavement surface caused by the upward migration of asphalt binder in an HMA pavement. It is also called “flushing.” In PCC “bleeding” is the flow of mixing water from freshly placed PCC.

Block cracking
In flexible pavements, interconnected cracks that divide the pavement up into rectangular pieces.

Blowup (or buckling)
A localized upward PCC slab movement and shattering at a joint or crack. Usually occurs in spring or summer and is the result of insufficient room for slab expansion during hot weather.

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, which is the beginning of the curing process.

The practice of texturing a freshly placed PCC surface by dragging a stiff broom across it.


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

Having cementing properties (set and harden in the presence of water).

Cement mortar
A combination of cementitious material (usually portland cement), water and sand (fine aggregate). It does not include coarse aggregate.

Cement paste
A combination of cementitious material (usually portland cement) and water. It does not include any aggregate.

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 79°C (175°F) for dense-graded HMA. The grade of PG binder is known to have somewhat of an effect on cessation temperature.

Hairline surface cracks in an HMA mat caused by steel wheel rollers. Usually a result of over-compaction or attempting to compact the mat below cessation temperature.

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

An intermediate substance in the production of portland cement. Made of heated calcium silicate, clinker is usually in the form of small gray-black pellets. Clinker is subsequently cooled and pulverized into a fine powder that almost completely passes through a 0.075 mm (No. 200) sieve and fortified with a small amount of gypsum to form portland cement.

Coarse Aggregate
Defined by the Asphalt Institute (2001) as the fraction of aggregate retained on the No. 8 (2.36 mm) sieve. Defined by AASHTO M 147 as hard, durable particles or fragments of stone, gravel or slag retained on the No. 10 (2.00 mm) sieve.

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.

Composite pavements
Combination HMA and PCC pavements. Occasionally, they are initially constructed as composite pavements, but more frequently they are the result of pavement rehabilitation (e.g., HMA overlay of PCC pavement). Officially, the FHWA “composite pavement” category is defined as a “mixed bituminous or bituminous penetration roadway” of more than 25 mm (1 inch) of compacted material on a rigid base (from the FHWA).

Contraction joint
A sawed, formed, or tooled groove in a concrete slab that creates a weakened vertical plane. It regulates the location of the cracking caused by dimensional changes in the slab.

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 property 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.

The process of making the freshly placed PCC into a more uniform and compact mass by eliminating undesirable air voids (entrapped air) and causing it to move around potential obstructions (such as reinforcing steel). Sometimes this process is referred to as “compaction” however this Guide attempts to make a distinction between consolidating PCC and compacting HMA – two very different processes.

Construction joint
A discontinuity in a PCC pavement where placement has been halted for an extended period of time. For example, a construction joint is made when paving stops at the end of a work day. Construction joints can be placed both transversely and longitudinally.

Corner break
A crack that intersects the PCC slab joints near the corner.

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.

Continuously Reinforced Concrete Pavement. CRCP uses reinforcing steel for crack control. Cracks are allowed to form and held tightly together by underlying reinforcing steel.

Crude Oil
Unrefined petroleum.

The maintenance of satisfactory moisture and temperature within a PCC mass as it sets and hardens such that the desired properties of strength, durability and density can develop (from the Portland Cement Association).


“D” cracking
See “durability cracking”.

Dowel Bar Retrofit. Rehabilitation process performed on aged JPCP rigid pavements to reestablish load transfer between pavement slabs.

Localized pavement surface areas with slightly lower elevations than the surrounding pavement.

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.

Diamond grinding
A rigid pavement maintenance action where gang-mounted diamond saw blades are used to shave off a thin top layer of an existing PCC surface in order to restore smoothness and friction characteristics.

Dowel bars
Short steel bars that provide a mechanical connection between slabs without restricting horizontal joint movement. They increase load transfer efficiency by allowing the leave slab to assume some of the load before the load is actually over it.

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

A measure of how asphalt binder or PCC physical properties change with age. In general, as an asphalt binder ages, its viscosity increases and it becomes more stiff and brittle (sometimes called age hardening), and as a PCC ages freeze-thaw cycles and chemical attack degrade it.

Durability cracking
In PCC, a series of closely spaced, crescent-shaped cracks near a joint, corner or crack. It is caused by freeze-thaw expansion of the large aggregate within the PCC slab. Durability cracking is a general PCC distress and is not unique to pavement PCC.

Dynamic viscosity (also called “absolute viscosity”)
A measure of the viscosity of asphalt with respect to time, measured in poises, conducted at 60°C (140°F).


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.

Entrained air
Air included in PCC on purpose. Entrained air is usually added to mitigate the effects of freeze-thaw damage.

Entrapped air
Air present in PCC but not included by design. Entrapped air usually is not sufficient to mitigate freeze-thaw damage due to its low volume and poor dispersion.

Expansion joint
An intentional discontinuity in a PCC pavement placed at a specific location to allow the pavement to expand without damaging adjacent structures or the pavement itself.

Expected pay
The pay a contractor can expect for consistently producing material at a particular quality level. Expected pay is not necessarily the same as the pay factor shown in the specification for that quality level.

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 (also called “alligator cracking”)
Cracks caused by fatigue failure of an HMA surface (or stabilized base) under repeated traffic loading.

In rigid pavement, a difference in elevation across a joint or crack. Usually the approach slab is higher than the leave slab due to pumping, the most common faulting mechanism.

Full-Depth Reclamation (full-depth CIR). 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.

A measure of the particle size of portland cement.

Fixed form PCC paving
One of two chief methods of PCC paving. In fixed form paving, side forms are used to hold fresh PCC in place at the proper grade and alignment until it sets and hardens. These forms may also serve as tracks for various pieces of placing and finishing equipment.

Flexible pavement
Pavements that are surfaced with bituminous (or asphalt) materials as the surface course. These can be either in the form of pavement surfaces such as a bituminous surface treatment (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.

Running a flat surface across freshly placed PCC in order to eliminate high and low spots, embed larger aggregate particles beneath the surface, remove slight imperfections and compact the mortar at the surface in preparation for texturing (PCA, 1988).

Flushing (also called “bleeding”)
A film of asphalt binder on the pavement surface caused by the upward migration of asphalt binder in an HMA pavement.

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 (its 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 of fines from the subgrade into the base material, 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.

Ground Penetrating Radar
Ground penetrating radar (GPR) is a noninvasive tool that has been used to map subsurface conditions in a wide variety of applications. Many of these applications are well suited for evaluation of highway systems to determine pavement thickness and condition. GPR is basically a subsurface “anomaly” detector, as such it will map changes in the underground profile due to contrasts in the electromagnetic conductivity across material interfaces. In a GPR system, short pulses of radio wave energy travel through the pavement structure and create echos at boundaries of dissimilar materials, such as at an asphalt-base interface.


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.

Chemical reaction involving the addition of water. In portland cement, the chemical compound constituents undergo a series of chemical reactions in the presence of water that cause it to harden (or set).

Hydraulic cement
An inorganic material or a mixture of inorganic materials that sets and develops strength by chemical reaction with water by formation of hydrates and is capable of doing so under water (from ASTM C 125 and the Portland Cement Association).


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 its original location.

Isolation joint
An intentional discontinuity in a pavement used to lessen stresses that may develop due to differential movement between a pavement and a structure or another existing pavement.

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.

Joint reflection cracking
Cracks in a flexible overlay of a jointed rigid pavement. The cracks occur directly over the underlying rigid pavement joints.

Jointed Plain Concrete Pavement. The most common type of rigid pavement, JPCP controls cracks by dividing the pavement up into individual slabs separated by contraction joints.

Jointed Reinforced Concrete Pavement. JRCP controls cracks by (1) dividing the pavement up into individual slabs separated by contraction joints and (2) using reinforcing steel within each slab to control within-slab cracking.



Lane/shoulder drop-off
A difference in elevation between the traffic lane and the shoulder.

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

Lean concrete
PCC that contains less portland cement paste than a typical PCC.

Load Equivalency Factor. The output from the ESAL equation. This factor relates various axle load combinations to the standard 80 kN (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. Typically refers to flexible pavements. HMA is often placed in multiple layers based on compaction and smoothness considerations.

Linear cracking
PCC panel cracks not associated with corner breaks or blowups that extend across the entire slab.

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).

Load transfer
The transfer or distribution of load across pavement discontinuities such as joints or cracks (from the 1993 AASHTO Guide).

Longitudinal cracking
In flexible pavements, cracks parallel to the pavement’s centerline or laydown direction. Usually a type of fatigue cracking.

An amount of material or items of similar origin grouped together for quality analysis purposes.