Glossary of Pavement Terms

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link.

- A -

A.D.A.: The Americans with Disabilities Act. This comprehensive federal act was passed to ensure uniform compliance with standards for the benefit of those with disabilities. It's scope encompasses everything from the width of doorways and force required to open them to the use of Braille in elevators to assist the visually impaired. Most common in relation to pavement are the standards for disabled parking, access aisles, curb ramps, signage and markings etc. Some states and municipalities also have laws which regulate proper accessibility for the disabled.

Asphalt: Originally a naturally occurring product in use for centuries the early 1900's brought today's refined petroleum product. This term is often applied to almost any asphalt product from H.M.A.C. to asphalt cements and oils.

Asphalt Cement: A dark brown to black cementitious material in which the predominating constituents are bitumens which occur in nature or are obtained in petroleum processing. In varying proportions, asphalt is a constituent of most crude petroleum.

- B -

Base: Generic term for material installed prior to asphalt paving. May be a crushed stone product or asphalt product (see full-depth asphalt pavements). The base material provides the load bearing characteristics of the finished pavement and may vary from 3-4" for a residential driveway to 18" or more for parking areas or roadways. The correct type and amount of base material must be determined and specified prior to paving. Lack of adequate base material is a primary cause of pavement failures.

Blacktop: Common "slang" term for asphalt. However this term should not be used in requesting any specifications or work as the term is widely used with various meanings in different areas. For example sometimes "blacktop" is used to refer to a penetration pavement or hot oil treatment or even sealcoating.

BST: An industry abbreviation for bituminous surface treatment, such as chip seal, fog seal, slurry seal, cape seal, etc.

- C -

Cape Seal: A combination of 2 common maintenance procedures. First the application of a chip seal (with or without crack sealing as needed) followed by the application of a slurry seal. This more expensive process provides extra structure & aggregate from the chip seal but a smoother surface, less prone to raveling, by the application of the slurry seal top coat.
Chip Seal: A process of applying a layer of hot asphalt oil over existing pavement the immediately covering with a thin layer of small crushed aggregate. The aggregate is then "rolled in" with a pneumatic roller. Is generally not used on parking facilities as the oil may "bleed" and cause tracking in hot weather.

C.I.P.R.: Abbreviation for Cold In Place Recycling. A general term for processes using grinding machines to recycle pavement into base material for new paving. Often using additives such as emulsions or foamed asphalt for stabilization.

Coal-Tar: A by-product of coke ovens in the steel production industry. Refined coal-tar has been used as a base for asphalt pavement sealers since 1938. It has become more expensive in recent years due to the shift in steel production to foreign countries.

Course, Asphalt Base

A foundation course consisting of mineral aggregate, bound together with asphalt material.

Course, Asphalt Surface

The top course of an asphalt pavement, sometimes called asphalt wearing course.

- D -

Drag Box Spreaders: Drag Boxes (so called because they are pulled behind a dump truck or other vehicle) are sometimes used to spread asphalt. While it is not impossible to do a reasonable job with one of these devices, the discrepancies in the resulting finished surface usually result in an inferior job. These type devices, sometimes home-made, are often used by so-called "traveling" or "fly-by-night" contractors. These devices are characterized by the lack of a floating screed (see screed).
These devices should not be confused with manufactured tow-behind pavers which have floating screeds, which when used with skill produce an asphalt mat comparable to a regular self-propelled paver.

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Emulsion: Mechanically produced combination of ingredients which do not normally mix. For example, asphalt emulsions are made by a procedure which mechanically mills the warm asphalt into minute globules, dispersing them in water, and adding a small amount of an emulsifying agent. Most of today's "asphalt oils" as well as sealcoatings for parking areas driveways, and roadways use emulsions because they are far more enviromentally freindly than older formulas that contained solvents.

- F -

Fog Seal: A process of applying a highly diluted asphalt emulsion in a fine spray (fog) to a roadway surface. Restores blackness and seals hairline cracks, may prevent or slow oxidation. Not generally used for parking facilities due to potential tracking problems.


Full-Depth Asphalt Pavement: The process of constructing an asphalt pavement structure using asphalt products for all components. The base material and surface courses are all made up of appropriately specified grades of hot-mix asphalt in contrast to conventional paving using crushed stone materials etc. There are numerous benefits to this method of construction. The Asphalt Institute has excellent detailed information about this process. A link is available on this site.

- G -

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

Gilsonite: Gilsonite, or North American Asphaltum is a natural, resinous hydrocarbon found in the Uintah Basin in northeastern Utah. Gilsonite in mass is a shiny, black substance similar in appearance to the mineral obsidian. It is brittle and can be easily crushed into a dark brown powder. Some companies manufacture pavement sealers with Gilsonite as a base material. A drawback to these sealers is the necessity of solvents, usually mineral spirits (paint thinner) to dissolve the Gilsonite. Improperly or over-applied these solvents can damage asphalt pavements.

- H -

Heat Lance: Device using a combination of propane and compressed air ignited in a specially designed chamber to produce an extremely hot high-velocity stream of air. Used to remove debris and vegetation from pavement cracks prior to sealing. It also warms and dries the crack to better accept the sealant. When properly used federal research has determined this to be a most effective preparation method (SHRP H-106 Data). Although more expensive initially the combination of routing and heat lance preparation can provide 10 times the life of conventional crack sealing methods.

H.M.A.C.: Hot Mix Asphalt Concrete. Abbreviation of the proper name for what is commonly referred to as "asphalt", "hot-mix", "blacktop" etc. This term should always be used in specifying asphalt pavement work to avoid any confusion or misinterpretation of the material desired. H.M.A.C. is produced in many different grades from coarse base mixes to specialized mixes for surfacing and repair. In most instances the grades are specified according to state department of transportation guidelines.

Hydrophobic:: Liquid composition additive to reduce curing time of surface coatings:; As applied to asphalt sealcoatings this is generally a product used in an "additive" fashion or manufactured into the sealcoat to cause faster drying. Preferably, the additive is composed of a composition of water; calcium chloride granules; citric acid granules; and an ammonium dispersing composition. Alternatively, aluminum sulfate may be utilized in place of calcium chloride and citric acid.

- I -

Infra-Red: Asphalt surface repair process which uses radiated heat to soften existing pavement. Most commonly the pavement is then raked and additional hot mix added. When raking is completed to grade, the area is re-compacted. This allows fast repairs with less new material and facilitates repairs in weather to cool for conventional methods. Not appropriate for areas of base failure or requiring structural repair. May also be used to soften pavement for texturing or decorative processes such as Street Print^®.

I.S.A.: International Symbol of Accessibility. The correct term for what is often referred to as a "handicap symbol". This familiar wheelchair design is used worldwide to denote areas designed to facilitate access for those with disabilities. (See also A.D.A.)

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Laydown: The portion of the asphalt paving process where the hot asphalt is actually placed or "laid down" by the paving machine.

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

- N -

Naphtha

A common solvent, most often called "paint thinner". In relation to asphalt the type solvent generally used in "Gilsonite" based products and most "rejuvenating" products to partially dissolve the asphalt to allow the base ingredients to "soak in".

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- O -

OTC: The Ozone Transport Commission. An air quality consortium currently affecting 13 NE and NE Coastal states. As related to pavement they have passed legislation limiting products with high VOC (volatile organic compound) levels. In these 13 states this has resulted in contractors no longer being able to use conventional solvent based striping paints, pavement sealers containing Gilsonite, or products marketed as "asphalt rejuvenators" which contain high levels of solvents.
Conventional sealers such as coal tar emulsion or asphalt emulsion are not affected and paint manufacturers have new formulations of paint for use in the striping industry in these states.
(Note: In most of these states these products became illegal to transport, sell, or apply Jan. 1, 2005 however a couple of states are "phasing in" the requirements. A web search for the Ozone Transport Commission will find their site for the most current status. This trend towards developing tighter air quality standards for entire regions is expected to expand.)

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Paving Machine (paver): The piece of equipment used to place the asphalt or concrete materials in their finished position.; In asphalt construction these machines should be the appropriate size for the project. The primary characteristic of all asphalt pavers is a floating screed (see screed). The machine must be able to place a consistently smooth, even finish at the proper depth and provide initial compaction.; In concrete construction pavers are normally only used on large commercial or highway projects. They are capable of placing the concrete at the specified depth with the appropriate reinforcing steel and providing compaction and an initial finish.

Permeable (porous asphalt) Pavements: Permeable Pavements are a relatively new form of asphalt paving. The entire process "from the ground up" is different than conventional asphalt pavements.
The basic principle is that these pavements, unlike conventional asphalt pavement, allow water to pass through the asphalt surface into the base material underneath. In these type pavements the base material is also different and designed as either a reservoir for holding the water or with a drainage system to direct the water to alternative drainage systems. They are most suited for use on highways or other high-speed areas where low grade slope prevented water to drain from the surface quickly contributing to hydroplaning and dangerous conditions. There is also evidence these pavements may sometimes produce lower sound levels from tire noise in urban environments where this is a factor for adjacent areas.
However recently these type pavements have started being used in more conventional settings such as commercial or in rare cases residential applications where localities are concerned with "runoff" issues for whatever reason.
The technology is really quite simple. The secret to success is to provide the water with a place to go, usually in the form of an underlying, open-graded stone bed. As the water drains through the porous asphalt and into the stone bed, it slowly infiltrates into the soil. The stone bed size and depth must be designed so that the water level never rises into the asphalt. This stone bed, generally up to 36 inches in depth, provides a tremendous subbase for the asphalt paving.; These type pavements have many advantages however they also have major disadvantages for many uses when not absolutely required. Porous pavements MUST be engineered & designed for each individual application. There is no common specification for this type pavement. Not only is there great variation in permeable asphalt mixtures the soils must be sampled, the base materials specified, and drainage designed taking all these factors into account. In layman's terms this design is needed because much like a septic system there must be adequate provision for the water which drains through the permeable pavement to either be absorbed by the surrounding soil without loss of stability or drained by other methods to an approved drainage system. Thus many factors such as the average rainfall amounts, volume of water to be drained under "worse case" scenarios, absorptive properties of the soils, etc. must all be accounted for and the entire porous pavement structure designed and installed to exacting specifications for permeable pavements to function properly.
Of note as a downside for "off-road" or smaller project uses are greatly increased engineering/design costs, more difficulty in finding contractors experienced with permeable pavements, the inability to perform some maintenance (such as sealcoating, which would defeat the entire process), the inability in cold climates to use de-icing materials such as sand (which would clog the structure) or some chemical deicing agents (which could pose environmental problems) and the need for increased regular cleaning of the pavement to keep the pores open and allow the drainage properties to remain intact. However when constructed properly these pavements can have a good lifespan of over 20 years without failure or cracking.
Pervious or porous concrete: Pervious concrete is a mixture of gravel or stone, cement, water and sand. Using little or no sand in this mixture creates an open cell structure that allows water and air to pass through. When pervious concrete is used for paving, this open cell structure allows storm water to filter through the pavement and into the underlying soils or act as a retention area. This can be used for traffic or non-traffic areas.
Concerns about clogging of porous concrete pavements can be designed out”, by reducing erosion and sediment runoff through strategic design and water retaining ground cover. Studies indicate that pressure washing a “clogged” porous concrete pavement can restore 80-90% of the permeability.
Projects have been done, for example, where a new parking lot was designed so that rainwater would drain to the pervious concrete parking areas. That design also included a system to collect and reuse the rainwater collected from the pervious concrete for irrigation during the dry season. The designers were able to create an environmentally friendly and aesthetically pleasing parking lot with the help of pervious concrete pavements.

Prime Coat: A coating of asphalt oil either cutback or specialized emulsion, used to seal the sub-base and/or base material and enhance bonding to the asphalt course.

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Quick setting additives: (Also see hydrophobic)
This term covers a broad spectrum of products but all are used to decrease the time before opening to traffic of various pavements, generally after maintenance procedures. As an example slurry seals or conventional sealcoating sometimes have these type additives used for particular projects to allow areas to be re-opened to traffic more quickly. There are as many different additives of this type as there are products and procedures for their use.
Of note is that very generally speaking these type additives (unlike other specialty additives) usually only increase the "set" time of the product. Normally they have no significant addition of other properties such as extended durability, increased traction, or increased flexibility. While certainly very useful in many circumstances these products should only be expected to perform their intended purpose. They should not be used in cases where temperature is a factor however they may be useful when other factors are present such as predicted rainfall, shady conditions or higher humidity which could slow normal setting times, or other mitigating factors or in locations where traffic demands are such that an area must be re-opened to traffic with minimal closure times or for other reasons the product needs to be initially "set" faster than normal.
Of note concerning conventional sealcoating "quick set" additives is that there are some recently introduced products which claim tremendous reductions in the "time to traffic" (as little as a few hours) however initial reports from contractors trying these products indicate that while they do, as claimed, allow areas to be opened to traffic far faster than a normal "quick set" additive they also seem to have an adverse effect on durability and there have been numerous reports of unsatisfactory longevity when these products were used (some with reported reductions in coating life of 50-75% or more) which would negate any benefit from their use if longevity and cost-effectiveness of the sealcoating was an issue. These are, however, "contractor feedback" received by the association and not scientific or definitive results. The reports have been widespread enough to make them noteworthy however.

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- R -

R.A.P.: Abbreviation for Reclaimed Asphalt Pavement. Most commonly refers to ground asphalt which is added back into a virgin asphalt mixture at the mixing plant. This and related procedures using RAP are becoming common for economical and environmental reasons. Recycled pavements may have different performance characteristics than conventional mixtures. Larger contracts today should specify if the use of RAP materials is encouraged, allowed, or not allowed.


Reflective Cracking
: Cracks in an asphalt overlay pavement caused by cracks in the existing pavement "reflecting" up through the overlay. Specialized techniques and materials such a multi-membrane paving fabrics help reduce this problem.

Routing
: Enlargement of pavement cracks using a specialized machine. This provides a uniform width reservoir for the sealant. Proper choice of bit size will result in the proper depth to width ratio (depth=width). Properly used this procedure greatly increases the effectiveness and durability of crack sealing.

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Screed: The part of a paving machine which spreads, smoothes, and provides the initial compaction of the asphalt. Screeds actually "float" over the asphalt and their adjustment determines the finished thickness as well as the crown or valley profile of the asphalt mat.

Sealcoating: Application of a sealant (usually coal-tar emulsion or asphalt emulsion type) to preserve, protect, and beautify asphalt pavements. Generally used on low traffic streets or off-street locations. There are many different sealcoating products available from low-end "do-it-yourself" grades sold in buckets to commercial products. Commercial products are sold in bulk in concentrated form. Water, silica sand (or other suitable aggregates) and specialized additives are then added in precise ratios (mix design) by the contractor in an agitated mixing tank. Care should be taken to choose the appropriate product, mix design, and application method for the specific project and it's location.

S.H.R.P.
: Abbreviation for the Strategic Highway Research Program. This multi-year in depth federal research project provides much of the data used in determining today's most effective paving and pavement maintenance designs, materials, and methods.

Slurry Seal: A sealcoating process generally used on runways, streets, and roadways. In this process the coating is manufactured by the application equipment as it is being applied. A closely specified blend of graded asphalt emulsion, additives, and aggregate slurry seal is generally classified as Type I, II, or III depending on the size of aggregate used. A large aggregate slurry seal with additional polymers may also be referred to as microsurfacing. Used infrequently on parking areas due to the potential for tracking in hot weather.

StreetPrint^®

A proprietary decorative process in which steel templates in a variety of patterns are "imprinted" into hot asphalt pavement during the final compaction phase. A specialized colored sealer is then applied to give the appearance of brick, stone, or the particular pattern. An increasingly popular method of giving a custom appearance to asphalt pavements.

Subgrade

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

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- T -

Tack Coat: Asphalt oil, usually emulsion type, applied to existing pavement during repairs or overlay paving to create a bond between the old and new asphalt.
Tracking: The result of products or materials being "picked up" by car tires, shoes, shopping cart wheels, etc. and being carried from the pavement or "tracked" onto surfaces where the material is not desired.

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- U -

Underlayment:: Usually a fabric or various plastic multi-cell materials placed under asphalt pavement to either prevent the movement of the aggregate base on in some of today's applications to allow water to pass through the structure without clogging the drainage (see also Porous Pavement). This term can apply to a wide variety of materials and is usually defined by a preceding term such as: geotextile fabric underlayment.

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This section always under continuing development.

Revised: March 07, 2008. Copyright © 2000-2006 by The National Pavement Contractors Association. All trademarks or product names mentioned herein are the property of their respective owners.

Revised: March 07, 2008.
Copyright © 2000-2006 by The National Pavement Contractors Association.
All trademarks or product names mentioned herein are the property of their respective owners.