Glossary

From Pavement Interactive

Refer to the Glossary Guide for informatiton on how to add or change terms in the Glossary.

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A

AASHTO
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).

Acceptance
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.

ACI
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) http://www.aci-int.org

ACPA
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. http://www.pavement.com

Admixture
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.

Aggregate
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).

Agitation
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.

APA
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. http://www.asphaltalliance.com

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).

AQL
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.

Asphalt
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.

Asphaltenes
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. http://www.asphaltinstitute.org

B

Backcalculation
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.

Bitumens
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.

Bleeding
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.

Breaking
The phenomenon when asphalt and water separate in an asphalt emulsion, which is the beginning of the curing process.

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

C

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

Cementitious
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.

Checking
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.

CIR
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.

Clinker
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.

Consolidation
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.

Corrugation
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.

CRCP
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.

Curing
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

"D" cracking
See "durability cracking".

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

Depression
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.

Durability
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).

E

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).

Emulsion
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.

ESAL
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.

F

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

Faulting
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.

FDR
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).

FHWA
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. http://www.fhwa.dot.gov/ctdiv/history.htm

Fineness
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.

Floating
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.

Flux
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.

FWD
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.

G

Geotextiles
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.

H

HIPR
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.

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

HMAC
Hot Mix Asphalt Concrete. Another term for HMA.

Hydration
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).

I

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-situ
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.

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

J

JMF
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.

JPCP
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.

JRCP
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.

K

L

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

Laydown
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.

LEF
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.

Lift
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.

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

M

Macadam
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.

Maltenes
Non-polar or relatively low-polarity molecules within asphalt cement.

Mat
A term used to describe the fresh asphalt surface behind the paving machine. Most commonly used to refer to the asphalt during the placement 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.

Maturity
A term used to describe the estimated extent of PCC hydration by tracking time and temperature.

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

Mineral filler
A finely divided mineral product, at least 70 percent of which will pass a 0.075 mm (No. 200) sieve.

MTV
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 allowing the paver to operate continuously without stopping, minimizing truck waiting time at the paving site and minimizing segregation and temperature differentials.

N

NAPA
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.

NCAT
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.

Newtonian fluid
A fluid whose viscosity is constant at all shear rates. Since Isaac Newton first published the properties of an ideal fluid, ideal fluids are often called "Newtonian fluids".

NFS
Not Frost Susceptible.

Non-Newtonian fluid
A fluid whose viscosity is not constant at all shear rates. Some examples of non-Newtonian fluids are asphalt cement, cornstarch and water mixed together, ketchup and blood.

O

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

P

Pay factor
A multiple applied to the contract price of a particular item.

PCC
Portland Cement Concrete.

PD
Percent Defective. The percentage of the lot falling outside specification limits.

Permeability
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 begins to exhibit the properties of a semisolid.

Poiseuille, Jean Louis Marie
French physiologist and physician (1797-1869). Person for whom "poise", a unit of viscosity, is named after. Best known for his research on the physiology of the circulation of blood through the arteries. His interest in blood circulation led him to study the flow rates of other fluids. In 1840 he formulated the law regarding the flow rate for the laminar flow of fluids in circular tubes. In 1847 he published the results of further experiments using ether and mercury. Gotthilf Hagen, a German hydraulic engineer, discovered Poiseuille's law independently in 1839. (from Atomica, http://www.gurunet.com)

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.

Popouts
Small pieces of PCC that break loose from the surface leaving small divots or pock marks.

Portland cement
A hydraulic cement composed primarily of hydraulic calcium silicates (from the Portland Cement Association).

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

Pozzolan
A siliceous volcanic ash or artificial substance (such as fly ash) used to produce hydraulic cement.

Prime coat
An application of asphalt primer to an absorbent surface. Often used to prepare an untreated base for an asphalt surface. The prime coat 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.

PSI
Present Serviceability Index. A pavement condition index.

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

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

Punchout
In rigid pavements (especially CRCP), a localized slab portion broken into several pieces.

PWL
Percent Within Limits. The percentage of the lot falling above a lower specification limit, below an upper specification limit, or between upper and lower specification limits. PWL is related to PD by the following: PWL = 100% - PD.

Q

Quality
In its broadest sense, quality is a degree of excellence: the extent to which something is fit for its purpose. In the narrow sense, product or service quality is defined as conformance with requirement, freedom from defects or contamination, or simply a degree of customer satisfaction. In quality management, quality is defined as the totality of characteristics of a product or service that bears on its ability to satisfy stated and implied needs (from the Institute of Quality Assurance). In statistical acceptance plans "quality" is narrowly defined as the fraction of the overall quality characteristic distribution that falls within specification limits.

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 characteristic
Those material characteristics or properties that a particular acceptance plan measures to determine quality.

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.

R

RAP
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 discarded HMA pavement.

Raveling
In flexible pavements, the progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles.

RCM
Reclaimed Concrete Material. Same as RCP. When crushed, it can be used as a coarse aggregate in PCC, a granular base course or a fill/embankment material.

RCP
Recycled Concrete Pavement. Same as RCM. When crushed, it can be used as a coarse aggregate in PCC, a granular base course or a fill/embankment material.

Reactive aggregate
Those that either expand or develop expansive by products when introduced to certain chemical compounds.

Reactive aggregate distress
Pattern or map cracking (crazing) on the PCC slab surface caused by reactive aggregates.

Ready-mixed concrete
PCC that is delivered to the customer in a freshly mixed and unhardened state (from the National Ready Mix Concrete Association).

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

Residuals
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
Eliminated from Superpave specifications in late 2002. A particular area of the FHWA’s 0.45 power gradation graph associated with Superpave mix designs. It was observed that mixes closely following the 0.45 power maximum density line sometimes had unacceptably low VMA. Therefore, Superpave introduced a restricted zone through which a typical gradation should not pass. By avoiding the restricted zone, mixes should have sufficient VMA to allow enough asphalt for adequate durability.

RHM
Recycled Hot Mix.

Rice density (also called "TMD")
The theoretical maximum density of an HMA if it contained zero air voids.

Rigid Pavement
Pavements that are surfaced with PCC in the surface course. Since PCC has a high modulus of elasticity, rigid pavements do not flex appreciably to accommodate traffic loads.

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.

RQL
Rejectable Quality Limit. The maximum level of actual quality at which a material or construction can be considered unacceptable and thus, rejectable.

Rubblization
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.

Rutting
Surface depressions in the wheelpath of a pavement.

S

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

Screeding
A process in PCC paving where excess portions of the roughly placed PCC are cut off in order to bring the slab to the required elevation. This is usually done by dragging a straightedge across the slab at the required elevation.

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, microsurfacing, and BSTs.

Segregation
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."

SHA
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.

Shewhart, Dr. Walter A.
The "father of modern quality control". Shewhart successfully brought together the disciplines of statistics, engineering, and economics and became known as the father of modern quality control. The lasting and tangible evidence of that union for which he is most widely known is the control chart, a simple but highly effective tool that represented an initial step toward what he called "the formulation of a scientific basis for securing economic control." (from the American Society for Quality web site).

Shoving
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.

Shrinkage cracking
Cracks formed due to material contraction either from temperature drops (both HMA and PCC) or water loss during setting and curing (PCC).

SHRP
Strategic Highway Research Plan.

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

Slipform PCC paving
One of two chief methods of PCC paving. Slipform paving is defined as a process used to consolidate, form into geometric shape and surface finish a PCC mass by pulling the forms continuously through and surrounding the plastic concrete mass.

Slippage cracking
In flexible pavements, crescent or half-moon shaped cracks generally having two ends pointed into the direction of traffic caused by breaking or turning wheels.

Slump
The distance a specified conical form of fresh PCC falls when the form is removed. The slump test involves hand placing an amount fresh concrete into a metal cone and then measuring the distance the fresh PCC falls (or "slumps") when the cone is removed.

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.

Soundness
Term often used to (1) describe an aggregate's weathering resistance characteristics or (2) the ability of a hardened cement paste to retain its volume after setting without delayed destructive expansion.

Spalling
In rigid pavement, cracking, breaking or chipping of joint/crack edges.

Specification, end-result
A specification in which the final characteristics of the product are stipulated, and the contractor is given considerable freedom in achieving those characteristics.

Specification, method
A specification that outlines a specific materials selection and construction operation process to be followed in providing a product.

Specification, performance
A specification in which the product payment is directly dependent upon its actual performance.

Specification, statistical acceptance
A formal acceptance procedure based on statistical methods.

Warranty Specifications|Specification, warranty
A type of performance specification where the agency specifies pavement performance only and the contractor warrants the pavement for performance over a specific amount of time. During the warranty period, any defects attributable to construction are repaired at the contractor’s expense.

Specification, proprietary product
A specification used when a generic description of a desired product or process cannot be easily formulated. It usually contains an "or equivalent" clause to allow for some measure of competition in providing the product.

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

Stabilized aggregate or soil
Aggregate or soil to which a stabilizing agent has been added in order to bind otherwise loose particles to one another, providing strength and cohesion. The stabilizing agent is usually some sort of cementitious or bituminous material.

Stripping
In flexible pavements, the loss of bond between aggregates and asphalt binder that typically begins at the bottom of the HMA layer and progresses upward. When stripping begins at the surface and progresses downward it is usually called raveling.

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

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

Superpave
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.

T

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 (also called "transverse cracking")
Cracking caused by shrinkage of the pavement surface due to low temperatures.

Thixotropic
The property exhibited by certain substances of becoming less viscous when agitated and returning to a more viscous state upon standing. "Thixotropic" comes from the Greek words thixis, which means "the act of handling" and trope, meaning "change".

Tie bars
Either deformed steel bars or connectors used to hold the faces of abutting slabs in contact. Although they may provide some minimal amount of load transfer, they are not designed to act as load transfer devices and should not be used as such (from the 1993 AASHTO Guide).

TMD (also called "Rice density")
Theoretical maximum density. The theoretical maximum density of an HMA if it contained zero air voids.

TMG
Traffic Monitoring Guide.

Transverse cracking (also called "thermal cracking")
Cracking caused by shrinkage of the pavement surface due to low temperatures.

U

UTW
Ultra-Thin Whitetopping. Whitetopping where the PCC overlay is in the 50 - 100 mm (2 - 4 inch) range.

V

VMA
Voids in the Mineral Aggregate. 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.

VMT
Vehicle Miles Traveled. The total number of miles traveled by all vehicles.

W

Water-cement ratio
The volume of water in relation to the volume of portland cement. Usually expressed as a decimal (e.g., 0.35).

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.

Wheelpath
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.

Whitetopping
A PCC overlay of an existing flexible pavement.

Workability
A term that refers to a material's ability to be placed and compacted. Workable mixes are easy to place and compact and are generally less viscous than mixes with poor workability.

X

Y

Z

Note: This glossary was put together using resources from the Pavement Guide Interactive as well as some guidance obtained by viewing the glossaries of the Asphalt Institute and National Pavement Contractor's Association (NPCA), American Concrete Pavement Association (ACPA) and some definition help using Atomica's Atomica Personal desktop utility.