Common Asphalt Terms  
 
Aggregate
A hard inert mineral material, such as gravel, crushed rock, slag, or crushed stone, used in pavement applications either by itself or for mixing with asphalt.

Alligator Cracks
Interconnected cracks forming a series of small blocks resembling an alligator's skin or chicken-wire, and caused by excessive deflection of the surface over unstable subgrade or lower courses of the pavement.

Base Course
The layer in the pavement system immediately below the binder and surface courses. It usually consist of crushed stone, although it may consist of crushed slag or other stabilized or unstabilized material.

Bitumen
A class of black or dark-colored (solid, semisolid, or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, of which asphalts, tars, pitches and asphaltites are typical.

Crack
An approximately vertical random cleavage of the pavement caused by traffic loading, thermal stresses and/or aging of the binder.

Edge Joint Cracks
The separation of the joint between the pavement and the shoulder, commonly caused by the alternate wetting and drying beneath the shoulder surface. Other causes are shoulder settlement, mix shrinkage, and trucks straddling the joint.

Hot Mix Asphalt
An engineered mixture of aggregate, or stones and sand, with liquid asphalt cement, a petroleum product. Varying sizes of aggregates are heated, then mixed, in exact proportions, with asphalt cement that has been liquefied at about 300 degrees. While the mixture is still hot, it is delivered to your driveway and paved on top of a base or subgrade that has already been prepared. Very soon after paving, the mixture cools and hardens and you can drive on it right away.

Overlay
The placement of hot asphalt over existing asphalt bound with a tack coat. AKA - Resurfacing, skins.

Seal Coat
A thin surface treatment used to improve the surface texture and protect an asphalt surface. The main types of seal coats are fog seals, sand seals, slurry seals, micro-surfacing, cape seals, sandwich seals and chip seals.

Viscosity Grading
A classification system of asphalt cements based on viscosity ranges at 60ºC (140ºF). A minimum viscosity at 135ºC (275ºF) is also usually specified. The purpose is to prescribe limiting values of consistency at these two temperatures. 60ºC (140ºF) approximates the maximum temperature of an asphalt pavement surface in service in the U.S. 135ºC (275ºF) approximates the mixing and laydown temperatures for hot mix asphalt pavements.