Paving Terminology

Absolute Viscosity The measure of the viscosity of a fluid, equal to the force per unit area required to maintain a difference of velocity of one unit distance per unit time between two parallel planes in the fluid that lie in the direction of flow and are separated by one unit distance: usually expressed in poise or centipoise.
Aggregate Spreaders A piece of equipment used for placing aggregate to a desired depth on a roadway or parking lot.
Aggregate A material or structure formed from a loosely compacted mass of fragments or particles.
Air Voids Are small airspaces or pockets of air that occur between the coated aggregate particles in the final compacted mix.
Asphalt A mixture of dark bituminous pitch with sand or gravel, used for surfacing roads, flooring, roofing, etc.
Alligator Cracks Also called fatigue cracking or alligator cracking, is a common type of distress in asphalt pavement. It is usually studied under the transportation section of civil engineering.
Asphalt Concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac or bitumen macadam in Great Britain and Ireland) is a composite material commonly used to surface roads, parking lots, and airports.
Asphalt Emulsion Within the colloid mill the Asphalt is brought into intimate contact with a chemical solution. This is the chemical stabilization. After discharge the emulsion consists of water with fine particles of Asphalt dispersed in it, all that is between the particles and each other is water and chemicals.
Asphalt Emulsion Slurry Seal A mixture of slow-setting emulsified asphalt, fine aggregate, and mineral filler with a slurry consistency.
Asphalt Pavements Pavements consisting of a surface course of asphalt concrete over supporting courses such as asphalt concrete bases, crushed stone, slag, gravel, Portland Cement Concrete (PCC), brick, or block pavement.
Asphalt Prime Coat A prime coat is an application of a low viscosity asphalt to a granular base in preparation for an initial layer (or surface course layer) of asphalt.
Asphalt Primer A liquid asphalt of low viscosity that is applied to a nonbituminous surface such as concrete to prepare the surface for an asphalt course.
Asphalt Rubber – Asphalt Concrete (AR-AC) is a road paving material made by blending ground-up recycled tires with asphalt to produce a binder which is then mixed with conventional aggregate materials. This mix is then placed and compacted into a road surface.
Asphalt Tack Coat A tack coat is a thin bituminous liquid asphalt, emulsion or cutback layer applied between HMA pavement lifts to promote bonding.
Asphaltenes Asphaltenes are molecular substances that are found in crude oil, along with resins, aromatic hydrocarbons, and saturates (i.e. saturated hydrocarbons such as alkanes). The word “asphaltene” was coined by Boussingault in 1837 when he noticed that the distillation residue of some bitumens had asphalt-like properties.
Automatic Cycling Control A control system in which the opening and closing of the weigh hopper
discharge gate, the bituminous discharge valve, and the pugmill discharge
gate are actuated by means of self-acting mechanical or electrical machinery
without any intermediate manual control. The system includes preset timing
devices to control the desired periods of dry and wet mixing cycles.
Back-calculation An analytical technique used to determine the equivalent elastic moduli of pavement layers corresponding to the measured load and deflections. In the iterative method, layer moduli are selected and adjusted until the difference between the calculated and measured deflections are within selected tolerances, or the maximum number of iterations has been reached.
Batch Plant A concrete plant, also known as a batch plant orbatching plant or a concrete batching plant, is a device that combines various ingredients to form concrete. Some of these inputs include sand, water, aggregate (rocks, gravel, etc.), fly ash, potash, and cement.
Bitumen A black viscous mixture of hydrocarbons obtained naturally or as a residue from petroleum distillation. It is used for road surfacing and roofing.
Blast-Furnace Slag Is a nonmetallic coproduct produced in the process. It consists primarily of silicates, aluminosilicates, and calcium-alumina-silicates. The molten slag, which absorbs much of the sulfur from the charge, comprises about 20 percent by mass of iron production.
Cape Seal A surface treatment where a chip seal is followed by the application of either slurry seal or micro-surfacing.
Clinker The stony residue from burned coal or from a furnace; a brick with a vitrified surface.
Coal Tar A thick black liquid produced by the destructive distillation of bituminous coal. It contains benzene, naphthalene, phenols, aniline, and many other organic chemicals.
Compaction The act of compressing a given volume of material into a smaller volume.
Consensus Properties Aggregate characteristics that must follow certain criteria to satisfy a Superpave mix design. Specified test values for these properties are not source specific but widely agreed upon. They include Coarse Aggregate Angularity, Fine Aggregate Angularity, Flat or Elongated Particles, and Clay Content.
Crack and Seat A fractured slab technique used in the rehabilitation of PCC pavements that minimizes slab action in a jointed concrete pavement (JCP) by fracturing the PCC layer into smaller segments. This reduction in slab length minimizes reflective cracking in new HMA overlays.
Curing The development of the mechanical properties of the asphalt binder. This occurs after the emulsion has broken and the emulsion particles coalesce and bond to the aggregate.
Deep Strength Asphalt Pavement Pavements containing at least four inches of HMA over non-stabilized base courses.
Deflection A load-induced, downward movement of a pavement section.
Densification The act of increasing the density of a mixture during the compaction process.
Design ESAL The total number of equivalent 80-kN (18,000-lb.), single-axle load applications (equivalent single axle loads) expected throughout the design period.
Disintegration The breaking up of a pavement into small, loose fragments caused by traffic or weathering (e.g. raveling).
Ductility The ability of a substance to be drawn out or stretched thin. While ductility is considered and important characteristic of asphalt cements in many applications, the presence or absence of ductility is usually considered more significant than the actual degree of ductility.
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.
Emulsifying Agent or Emulsifier The chemical added to the water and asphalt that keeps the asphalt in stable suspension in the water. The emulsifier determines the charge of the emulsion and controls the breaking rate.
Fatigue Resistance The highest stress that a material can withstand for a given number of cycles without breaking —called also endurance strength — compare fatigue limit.
Flexibility The ability of an asphalt pavement structure to conform to settlement of the foundation. Generally, flexibility of the asphalt paving mixture is enhanced by high asphalt content.
Fog Seal Is a light application of a diluted slow-setting asphalt emulsion to the surface of an aged (oxidized) pavement surface. Fog seals are low-cost and are used to restore flexibility to an existing HMA pavement surface.
Grade Depressions Localized low areas of limited size.
Hot Mix Asphalt (HMA) Is a combination of approximately 95% stone, sand, or gravel bound together by asphalt cement, a product of crude oil. Asphalt cement is heated aggregate, combined, and mixed with the aggregate at an HMA facility.
Impermeability The resistance an asphalt pavement has to the passage of air and water into or through the pavement.
Kinematic Viscosity A measure of the viscosity of asphalt, measured in centistokes, conducted at a temperature of 135°C (275°F).
Lane Joint Cracks Longitudinal separations along the seam between two paving lanes.
Lime Treated Subgrade A subgrade preparation technique in which the subgrade soil and added lime are mechanically mixed and compacted to produce a higher modulus base material than the in-situ material.
Maintenance Mix A mixture of asphalt emulsion and mineral aggregate for use in relatively small areas to patch holes, depressions, and distressed areas in existing pavements. Appropriate hand or mechanical methods are used in placing and compacting the mix.
Medium-Curing (MC) Asphalt Liquid asphalt composed of asphalt cement and a kerosene-type dilutent (thinner) of medium volatility.
Micro-Surfacing A mixture of polymer modified asphalt emulsion, crushed dense graded aggregate, mineral filler, additives and water. It provides a thin resurfacing of 10 to 20 mm (3/8 to 3/4 inch) to the pavement.
Mineral Filler A finely divided mineral product, at least 70 percent of which will pass a 0.075 mm (No. 200) sieve. Pulverized limestone is the most commonly manufactured filler, although other stone dust, hydrated lime, portland cement, and certain natural deposits of finely divided mineral matter are also used.
Modified Asphalt Rubber – Asphalt Concrete (MAR-AC) High quality, thoroughly controlled hot mixture of modified asphalt rubber binder (AR) and well-graded, high quality aggregate, which can be thoroughly compacted into a uniformly dense mass.
Natural (Native) Asphalt Asphalt occurring in nature, which has been derived from petroleum
through natural processes of evaporation of volatile fractions,
leaving the asphalt fractions. The native asphalt of most importance
is found in the Trinidad and Bermudez Lake deposits. Asphalt from
these sources is often called lake asphalt.
Open-Graded Aggregate One containing less-fine aggregate in which the void spaces in the compacted aggregate are relatively large and interconnected, usually 10% more.
Penetration Grading A classification system of asphalt cements based on penetration in 0.1 mm at 25°C (77°F). There are five standard penetration grades for paving: 40-50, 60-70, 85-100, 120-150, and 200-300.
Penetration The consistency of a bituminous material expressed as the distance (in tenths of a millimeter) that a standard needle penetrates a sample vertically under specified conditions of loading, time and temperature.
Plant Mix (Cold) An asphaltic concrete made with slow-curing asphaltsand used primarily as a temporary patching materialwhen hot mix plants are closed. Cold mix is used to repair potholes, but is less durable than hot mix.
Polished Aggregate Aggregate particles in a pavement surface that have been worn smooth by traffic.
Pumping Slab Deflection under passing loads sometimes resulting in the discharge of water and subgrade soils along joints, cracks and pavement edges.
Raveling The progressive separation of aggregate particles in a pavement
from the surface downward or from the edges inward.
Road Oil Asphalt cement and oils of low volatility, usually similar to one of the slow-curing (SC) grades.
Rubblization Is a construction and engineering technique that involves saving time and transportation costs by reducing existing concrete into rubble at its current location rather than hauling it to another location.
Sand Asphalt A mixture of ungraded sand and liquid asphalt used for an economical base or wearing surface for pavements.
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.
Sheet Asphalt A hot mixture of asphalt binder with clean, angular, graded sand and mineral filler. Its use is ordinarily confined to reservoir liners and landfill caps; usually laid on an intermediate or leveling course.
Subgrade The soil prepared to support a pavement structure or a pavement system. It is the foundation of the pavement structure.
Well-Graded Aggregate Aggregate graded with relatively uniform proportions, from the maximum size down to filler.