Aggregates — Various sized stones, crushed rock, gravel, etc. that make up approximately 92–96% of hot mix asphalt. (Asphalt cement makes up the other 4–8 %.)
Asphalt — The common name for “Bituminous Asphalt Concrete.” It is also known as “hot mix asphalt (HMA),” or “flexible pavement.” Asphalt is a mixture of aggregates and hot asphalt cement that, when placed, compacted and subsequently cooled, becomes the familiar asphalt pavement.
Asphalt Binder — A near-liquid 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 Cement — See “Asphalt Binder” above.
Asphalt Concrete — See definition of “Asphalt” above.
Asphalt Mix Design — An asphalt mix design is basically the recipe that sets forth what aggregate to use, what size range of aggregate to use, what asphalt binder to use, and what the best combination of these ingredients would be. The asphalt plant that produces the hot mix asphalt follows a mix design.
Blacktop — Common “slang” term for asphalt. This term should not be used in requesting any specifications or work, as the term has a broad variety of meanings in different contexts.
Chip Seal — A process of applying a layer of hot asphalt oil over existing pavement, then immediately covering the oil with a thin layer of small crushed aggregate. The aggregate is then “rolled in” using a pneumatic (rubber-tire) roller. Chip seals generally are not used on parking facilities because the oil might “bleed” and cause tracking in hot weather, but chip seals are often used on roads that experience low traffic volume.
Cold In Place Recycling (CIPR or CIR) — Cold in place recycling is a process where a machine grinds existing asphalt and base to a specified depth, then uses that ground-up material in the same location, creating a new base for a hot mix asphalt pavement. The recycled material is then compacted prior to paving. Often additives such as emulsions or foamed asphalt are added to the ground-up material to improve its stability.
Concrete — The common name for “Portland Cement Concrete Pavement.” A hard, compact building material formed when a mixture of cement, sand, gravel, and water dries. Typically used for sidewalks, curbs, and areas such as delivery docks, garbage pickups, or bus lanes that handle heavy vehicles.
Core Testing — A method of examining a constructed asphalt pavement to determine its depth and makeup.
Crack Routing — Crack routing requires the use of a special piece of equipment that follows the crack and creates a clean reservoir to accept the crack sealing material. Cracks can be sealed without routing (following cleaning with a heat lance), but research has proven that crack repairs that are first “opened up” with a router will last longer and are more effective at keeping water out of the pavement base and subbase.
Density — Asphalt pavements are constructed and compacted to a specific density as set forth in a contract or bid specifications by mechanically compacting (rolling) the hot material after it has been placed by the paving equipment. Density is not the same as compaction; density is achieved by compaction.
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. Also, the better drainage a pavement has, the less likely water will seep down into its base.
Emulsion — A mechanically produced combination of ingredients that do not normally mix. For example, asphalt emulsions are made by a procedure that mechanically mills the warm asphalt into microscopic globules, dispersing them in water, and adding a small amount of an emulsifying agent.
Fall — See “Slope” below.
Fog Seal — The process of applying a highly diluted asphalt emulsion in a fine spray (fog) to a roadway surface. Fog seals restore blackness and seal hairline cracks, and there is evidence that they help slow or even prevent oxidation. Not generally used for parking facilities due to tracking.
Geotextiles — The technical generic name for fabric-like materials used in the paving process. Geotextiles are manufactured with specific performance characteristics for specific uses such as stabilization of base material to prevent migration into sub-grades.
Grade — The degree to which a surface is angled to aid in the drainage of water, the act of leveling or sloping the subgrade or base layer before paving. See “Slope” below.
Heat Lance — Device using a combination of propane and compressed air ignited in a specially designed chamber to produce an extremely hot, directed high-velocity stream of air. Used to remove debris and vegetation from pavement cracks prior to sealing. A heat lance also warms and dries the crack so it better accepts the sealant. Federal research (SHRP H-106) has shown that, when used properly, a heat lance is the most effective preparation method for crack repair. Although more expensive initially, preparing cracks using a combination of routing and a heat lance can provide 10 times the life of conventional crack sealing methods.
Hot Mix Asphalt Concrete (HMAC) — The proper name for what is commonly referred to as “asphalt,” “hot-mix,” “blacktop,” etc. This term should always be used when specifying asphalt pavement work to avoid any confusion or misinterpretation of the material desired. HMAC is produced in many different grades from coarse (large aggregate) base mixes to specialized finer aggregate mixes for surfacing and repair. In most instances the grades are specified according to state Department of Transportation guidelines.
Joints — An asphalt joint is the area where two different “pulls” of asphalt paving meet. For example, if two 8-foot-wide lanes are paved side by side, the joint runs the length of the two lanes. This area is usually highly visible after the paving operation and is sometimes referred to as a “seam.”
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.
Reclaimed Asphalt Pavement (RAP) — 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. Pavements containing RAP might have different performance characteristics than conventional mixtures. Larger contracts today should specify if the use of RAP materials is encouraged, allowed, or prohibited.
Reflective Cracking — Reflective cracking refers to cracks in an asphalt overlay caused by cracks in the original pavement “reflecting” up through the overlay. Specialized techniques and materials, such as multi-membrane paving fabrics, help reduce this problem.
Slope — The degree to which a paved surface is angled to aid in the drainage of water.
Slurry Seal — A high-tech pavement maintenance resurfacing process generally used on streets and roadways. In this process the slurry sealcoating 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.) Rarely used on parking areas due to the potential for tracking in hot weather.
Soil or Subgrade Treatment — In some situations the condition of the soil (subgrade) that will support the pavement is unsuitable for paving. The soil might be too wet or might simply be unstable so it needs to be treated with lime or with a cement mixture to add strength to create a solid foundation on which to pave.
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 pavement or traffic. Subgrade failures can occur for a number of reasons, including: ground water, 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 base rock or lime/cement treated base. See “Patch Paving” above.
Superpave — 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 in which they will be constructed. Variables such as weather, the amount of traffic, the type of traffic, etc. are taken into account.
Tack Coat — Asphalt oil, usually an emulsion type, applied to existing pavement during repairs or prior to 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, or “tracked,” from the pavement onto surfaces where the material is not desired. More a concern for parking lots than roads.
Traffic Index Rating — A measurement of the amount of traffic a roadway or other asphalt surface is experiencing.
Transverse Crack — A break in the asphalt pavement that is at a 90 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 90 degree angle to the direction of the roadway or the direction in which the asphalt was laid.
Wedge Cut — The process where the existing asphalt layer is ground in a wedge shape to conform to an adjacent structure such as valley gutter, ramp, or curb and gutter. Typically done prior to the overlay process.