Pavement Terms

Aggregates

Various sized stones, crushed rock, gravel, etc., 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 becomes the familiar asphalt pavement when placed, compacted, and subsequently cooled.

Asphalt Mix Design

An asphalt mix design is the recipe that sets forth what aggregate to use, what size range of aggregate to use, what asphalt binder to use, and the best combination of these ingredients. 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

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 usually 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.

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 particular 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 water drainage, the act of leveling or sloping the subgrade or base layer before paving. See “Slope” below.

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

High-tech pavement maintenance resurfacing process generally used on streets and roadways. In this process, the slurry seal 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 micro surfacing.) 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 unstable, so it needs to be treated with lime or a cement mixture to add strength to create a solid foundation on which to pave.
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