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Glossary
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A
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.
Aggregate
A collective term for the mineral materials such as sand, gravel and crushed stone that can be used alone or with a binding medium (such as water, asphalt, 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.
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.
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).
Asphalt
A dark brown to black cementitious material in which the predominate 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 mm, 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
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 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.”
Block cracking
In flexible pavements, interconnected cracks that divide the pavement up into rectangular pieces.
Breaking
The phenomenon when asphalt and water separate in an asphalt emulsion.
Bulk Specific Gravity
A measure of density (mass per unit volume) as compared to the density of water at 73.4°F (23°C). By definition, water at 73.4°F (23°C) has a specific gravity of 1.
Bulk SSD Specific Gravity
A measure of density (mass per unit volume) of a substance that is saturated (water permeable pores are filled with water) yet surface dry as compared to the density of water at 73.4°F (23°C). By definition, water at 73.4°F (23°C) has a specific gravity of 1.
C
CBR
California Bearing Ratio. A strength test typically used on unbound 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. 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.
Compactive effort
The combined effect of (1) applying force to an HMA surface and compressing the material underneath the contact area and (2) creating a shear stress between the compressed material underneath the contact area and the adjacent uncompressed material.
Consensus requirements (properties)
A set of aggregate properties including minimum angularity, flat or elongated particles and clay content requirements. An expert group on aggregate properties was convened and arrived at a consensus on several aggregate property requirements for Superpave.
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.
Creep Compliance
The inverse of creep stiffness. Generally in units of (1/MPa). For asphalt cements, creep compliance tends to increase over time as a constant load is applied.
Crude Oil
Unrefined petroleum.
D
Depression
Localized pavement surface areas with slightly lower elevation 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. Typical gradations are near the 0.45 power curve but not right on it. Generally, a true maximum density gradation (exactly on the 0.45 power curve) would result in unacceptably low VMA.
Drum plant
A manufacturing facility for producing HMA. They manufacture HMA continuously rather than in batches.
Durability
For asphalt binder, durability is a measure of how asphalt binder 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). For HMA and aggregate, durability generally refers to an ability to withstand weathering (wetting and freeze-thaw cycles).
Dynamic viscosity (also called “absolute viscosity”)
The tangential force per unit area required to move one horizontal plane with respect to the other at unit velocity when maintained a unit distance apart by the fluid (Engineering ToolBox, 2004). In the SI system it is usually expressed as pascal-seconds, newton-seconds per meter squared or kilograms per meter-second where: 1 Pa·s = 1 N·s/m2 = 1 kg/m·s.
E
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 18,000 lb (80 kN) equivalent single axle load.
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.
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 the damage done by 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.
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. [from FHWA, http://www.fhwa.dot.gov/ctdiv/history.htm]
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.
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.
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.
G
H
HMA
Hot Mix Asphalt. A high quality, thoroughly controlled hot mixture of asphalt binder and aggregate that can be compacted into a uniform mass as a pavement.
HMAC
Hot Mix Asphalt Concrete. Another term for HMA.
I
In-situ
In place, in it’s original location.
Isotropic
Refers to properties that are the same regardless of the direction that is measured. Properties that are the same in all directions.
J
JMF
Job-Mix Formula. A recommended/specified mixture of aggregate and asphalt binder.
K
Kinematic viscosity
The ratio of dynamic (or absolute) viscosity to the density of a material. No force is involved in this quantity. In the SI system, it is commonly expressed in terms of meters squared per second or Stokes (St) where: 1 m2/s = 104 St.
L
Laydown
The portion of the HMA paving process where the HMA is actually placed or “laid down” by the paving machine.
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 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.
Longitudinal cracking
In flexible pavements, cracks parallel to the pavement’s centerline or laydown direction. Usually a type of fatigue cracking.
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. That portion of asphalt binder soluble in a specified solvent such as n-pentane.
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.
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 placing 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 possibly 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. [http://www.hotmix.org]
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. [http://www.eng.auburn.edu/center/ncat]
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”.
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
Oven dry
Sample that has been dried in an oven to ensure that water permeable pores are completely free of water.
P
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 designed so that any distresses are confined to the surfae layer and the only maintenance required is a periodic surface renewal.
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.
Pothole
Bowl-shaped distresses in a pavement resulting from localized disintegration.
Prime coat
An application of asphalt or asphalt emulsion to an untreated base prior to placement of a HMA 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 HMA layer.
Pycnometer
A specific gravity bottle; a standard flask for measuring and comparing the densities of liquids.
Q
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 monitor and adjust 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. HMA material taken up and processed during HMA pavement rehabilitation by milling machines or a special crushing plant.
Raveling
In flexible pavements, the progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles.
Reflective cracking
Cracks in HMA instigated by differential movement of cracks in lower pavement layers.
Residuals
The product remaining after petroleum refining. Sometimes referred to as “bottoms”.
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.
Rheology
Deformation and flow of material.
Rice density (also called “theoretical maximum density”)
The theoretical maximum density of an HMA if it had zero air voids.
Rutting
Surface depressions in the wheelpath of a pavement.
S
Saturated Surface Dry (SSD)
A specimen condition when the internal air voids are filled with water and the surface (including air voids connected to the surface) is dry.
Screed
The part of a paving machine that spreads, smoothes, and provides initial compaction for the HMA mat.
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 Agency.
Shear Flow
To undergo plastic deformation and movement without cracking or breaking.
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.
SHRP
Strategic Highway Research Program.
Skid resistance
The ability of a pavement to offer resistance to slipping or skidding. It is a one-sided measurement of the coefficient of friction. Generally a tire of known friction values is used to test for skid resistance. Measurements are usually done on a wetted pavement surface and can vary widely depending upon weather and time of year.
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.
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 preparatory maintenance or as a wearing course.
Soundness
Term often used to describe an aggregate’s weathering resistance characteristics.
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 specific materials 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.
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.
Specific gravity
A measure of density (mass per unit volume) as compared to the density of water at 73.4°F (23°C). By definition, water at 73.4°F (23°C) has a specific gravity of 1.
Stability
A term often used to describe an HMA’s ability to resist deformation under loading.
Stone matrix asphalt (SMA)
is a gap-graded HMA that is designed to maximize deformation (rutting) resistance and durability by using a structural basis of stone-on-stone contact. Because the aggregates are all in contact, rut resistance relies on aggregate properties rather than asphalt binder properties. Since aggregates do not deform as much as asphalt binder under load, this stone-on-stone contact greatly reduces rutting. SMA, originally developed in Europe to resist rutting and studded tire wear, has been used in the U.S. since about 1990.
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.
SSD – Saturated, Surface Dry
The condition in which the aggregate has been soaked in water and has absorbed water into its pore spaces. The excess, free surface moisture has been removed so that the particles are still saturated, but the surface of the particle is essentially dry.
Steric hardening
Progressive, reversible, isothermal increase in asphalt binder stiffness due to molecular rearrangement. Typically present in asphalt binder at intermediate or ambient temperatures (Planche et al., 2003).
T
Tender mix
An internally unstable mix (usually in a specific temperature range) that tends to displace laterally and shove rather than compact during construction. Internal mix stability is a function of asphalt binder viscosity and aggregate gradation and shape.
Tack coat
Liquid asphalt, usually an emulsion, applied to existing pavement during repairs or overlay paving to create a bond between the old and new asphalt.
Theoretical maximum density (also called “Rice density”)
Theoretical maximum density. The theoretical maximum density of an HMA if it contained no air voids.
Thermal cracking (also called “transverse cracking”)
Cracking caused by contraction 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”.
Transverse cracking (also called “thermal cracking”)
Cracking caused by shrinkage of the pavement surface due to low temperatures.
U
V
Viscosity
The resistance to flow caused by internal friction of a fluid.
Voids in the mineral aggregate (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.
W
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.
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 VSL as well as some guidance obtained by viewing the glossaries of the Asphalt Institute and National Pavement Contractor’s Association (NPCA) and some definition help using Gurunet’s desktop utility.
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