Paving Glossary

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.

Aggregates: Usually various sized stones, crushed rock, gravel, etc. that make up approximately 92-96% of the asphalt mixture. (Asphalt Cement makes up the other 4-8 %.)

Asphalt: The common name for "Bituminous Asphalt Concrete". It is also known as "flexible pavement." It is a mixture of aggregates and hot asphalt cement that when placed, compacted and subsequently cooled, becomes the familiar asphalt.

Asphalt Base: Asphalt mix where the largest stone used is no larger than 3/4 of an inch ( typically #57 gradation). Base mixes are usually laid over a stone base at a minimum depth of 2 inches compacted.

Asphalt Binder: The asphalt layer between the base layer of rock or other aggregate and the driving surface layer. The asphalt binder layer is usually made up of coarser materials and is usually thicker than the surface layer. The binder layer can be used as either a first layer or a driving surface, but its use is actually fairly limited. The vast majority of jobs call for a stone base layer, an asphalt base layer, then a surface layer.

Asphalt Cement: A petroleum byproduct used to "glue" the pavement together. By volume, this material makes up about 4-8% of the pavement mixture. (Aggregates make up the other 92-96%).

Asphalt Concrete: See definition of "Asphalt" above.

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.

Base Failure: Base failures occur when the layer beneath the binder layer and driving surface can no longer adequately support the weight of the structure or the traffic. Base failures can occur for a number of reasons, including: ground water, excessive load counts (too much weight), and inadequate design. The failure can be corrected by excavating the failed material and replacing it with bridging stone material.

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 (see fog seal).

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 (see fog seal).

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.

Compaction: Compressing a given volume of material into a lesser volume. A compacted subgrade and base is essential.

Concrete: The common name for "Portland Cement Concrete Pavement". A hard, compact buildingmaterial formed when a mixture of cement, sand, gravel, and water dries.

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.

Cracking: A separation of the asphalt layer due to excessive loads (weights), heat, or age.

Deflection: Deviation of a pavement from profile under weight loads.

Density ( thickness or compactness): Technically, density refers to the weight of a material at a specific volume (unit weight). A specific density of asphalt is achieved my mechanically compacting (rolling) the hot material after it has been placed by the paving equipment. To most consumers of asphalt, it means the compaction of the material versus a theoretical value that is usually derived in a laboratory.

Drainage: A system of drains and pipes for carrying away surface water. An asphalt surface is sloped to maximize the removal of surface water for vehicular safety.

Drag Box Spreaders: Drag Boxes (so called because they are pulled behind a dump truck) are sometimes used to spread asphalt. While it is not impossible to do a reasonable job with one of these, the discrepancies in the resulting finished surface usually result in an inferior job. These type devices, often home-made, are usually used by so-called "gypsy" or "fly-by-night" contractors. 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.

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

Fall: Slope. The degree to which a paved surface is angled to aid in the drainage of water.

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 tracking.

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.

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.

Grade: Slope. The degree to which a paved surface is angled to aid in the drainage of water. The act of leveling or sloping the subgrade or base layer before paving.

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.

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 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.)

Joints: An asphalt joint is the area where two different "pulls" of asphalt meet. This area is usually highly visible after the paving operation and is sometimes referred to as a "seam."

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

Limestone: A sedimentary rock often used as a building material, and for the base layer in an asphalt or PCCP paving system, and the major stone component for asphalt materials produced in our region.

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.

Nuclear Density: Measuring the density of a previously placed material achieved by using a special instrument designed to measure the penetration of radiation into that material.

Overlay: The practice of placing new asphalt over an existing asphalt or concrete surface. Also called resurfacing.

Portland Cement Concrete Pavement (PCCP): A hard, compact building material formed when a mixture of cement, sand, gravel, and water dries. Commonly known as concrete.

RAP (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.

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.

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.

Slope: The degree to which a paved surface is angled to aid in the drainage of water.

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.

Stone Base: The layer in the pavement system below the asphalt binder and driving surface. The base usually consists of crushed stones of varying sizes and gradations.

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

Subgrade Failure: Subgrade failures occur when the prepared soil beneath the asphalt structure can no longer adequately support the weight of the structure or the traffic. Subgrade failures can occur for a number of reasons, including: ground water, excessive load counts (too much weight), and inadequate design. The failure can be corrected by excavating the soft material from the affected area and replacing it with compacted soil or bridging stone material.

Superpave: Is short for "Superior Performing Asphalt Pavement". It is an asphalt design philosophy that uniquely designs roads, parking lots and other asphalt structures according to the environment. Variables such as weather, the amount of traffic, the type of traffic, etc. are taken into account.

Surface: Asphalt mix where the largest stone used is no larger than 1/8 an inch (typically #8 gradation). Surface mixes are usually laid at a minimum depth of 1inch compacted.

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.

Transverse Crack: A break in the asphalt pavement that is at a ninety degree angle to the direction of the roadway or the direction in which the asphalt was laid.

Transverse Joint: A joint in the asphalt pavement that is at a ninety degree angle to the direction of the roadway or the direction in which the asphalt was laid.

Wedging: Is a layer of asphalt applied as leveling prior to the application of the final driving surface of asphalt. The wedging layer is intended to even out any imperfections in the existing pavement prior to applying the final layer.