Alligator Cracking:

Interconnected or interlaced load associated (fatigue) cracks in asphalt concrete pavement forming a series of small polygons that resemble the typical pattern of an alligator's skin.

Asphalt Treated Permeable Base (ATPB):

A highly permeable open graded mixture of crushed coarse aggregate and asphalt binder placed as the base layer to assure adequate drainage of the structural section, as well as structural support.

Base Course:

A layer of selected, processed, and/or treated aggregate material of planned thickness and quality placed immediately below the pavement and above the sub base to support the pavement.


Also known as flushing, excess asphalt appears on the surface of the pavement, usually in the wheel paths. Accumulation with time may reduce skid resistance.

Block Cracking:

Interconnected cracks, which form a series of large polygons, usually with sharp corners or angles. Block cracking appears on flexible pavement but is not load associated.

Chip Seal:

A high viscosity asphaltic emulsion surface coat, which incorporates rolled in rock screenings (chips) over an asphalt concrete pavement, as preventive maintenance, to extend the service life.

Cold Recycling:

The rehabilitation of asphalt concrete pavement in place, without the application of heat, by milling and mixing with new binder and/or rejuvenating agents.

Composite Pavement:

A pavement structure or structural section composed of an asphalt concrete wearing surface and portland cement concrete (PCC) slab; an asphalt concrete overlay on a PCC slab is also referred to as a composite pavement.


Also known as 'wash board'. Transverse undulations appear at regular intervals due to the unstable surface course. This consists of alternating crests and valleys less than 2 feet apart and usually occurs where vehicles stop and start.

Crack Seals:

Pourable or extrudable materials that are placed in cracks to deter the entry of water and incompressible materials and to retard the crack from reflecting up into the asphalt concrete overlay.

Cushion Course:

The layer, generally an aggregate base material that is placed over an existing pavement to increase the profile grade and give additional structural support before placing the new asphalt concrete pavement.


A separation (debonding) of two layers of asphalt concrete generally due to insufficient binder during construction. It causes the two layers to act independently from each other.

Dense Graded Asphalt Concrete (DGAC):

A uniformly graded asphalt concrete mixture (aggregate and paving asphalt) containing a small percentage of voids, used primarily as a surface layer to provide the structural strength needed to distribute loads to underlying layers of the structural section.

Design Period:

The period of time that an initially constructed or rehabilitated pavement structural section is designed to perform before reaching its terminal serviceability or a condition that requires major rehabilitation or reconstruction; this is also referred to as the performance period. Because of the many independent variables involved, the service life before major maintenance or rehabilitation is required may actually be considerably longer or shorter.

Drip Path Ravel:

Progressive disintegration of the surface between wheel paths on asphalt concrete pavement, caused by oil and fuel dripping from vehicles. This is most prevalent adjacent to intersections where vehicles slow and stop.

Edge Drain System:

A drainage system, consisting of a slotted plastic collector pipe encapsulated in treated permeable material and a filter fabric barrier, with unslotted plastic pipe vents, outlets, and cleanouts, designed to drain the structural section of both rigid and flexible pavements.


A prism of earth that is constructed from excavated or borrowed natural soil and/or rock, extending from original ground to the grading plane, and designed to provide a stable support for the pavement structural section.

Equivalent Single Axle Loads (ESAL’s):

Summation of equivalent 18000-lb (80-kN) single axle loads used to convert mixed traffic to design traffic for the design period.

Flexible Pavement:

A traffic load carrying system that is made up of one or more layers that are designed to transmit and distribute that loading to the underlying roadbed material. The highest quality layer is the surface course, (generally asphalt concrete) this is usually underlain by a lesser quality base, and in turn a sub base. It is called flexible because it can tolerate deflection bending under heavy loads.

Fog Seal:

A combination of mixing-type asphaltic emulsion and water which is applied to the surface of asphalt concrete pavement to seal the surface, primarily used for pavement maintenance.

Grading Plane:

The surface of the basement material upon which the lowest layer of sub base, base, pavement surfacing, or other specified layer, is placed.

Hot Recycling:

The use of reclaimed asphalt concrete pavement which is combined with virgin aggregates, asphalt and sometimes rejuvenating agents at a central hot-mix plant and placed in the structural section in lieu of all new materials.

Lean Concrete Base:

Mixture of aggregate, portland cement, water, and optional admixtures, primarily used as a base for portland cement concrete pavement.

Leveling Course:

The layer, generally of AC or other treated or processed material, that is placed over the rough or undulating surface of an existing pavement, structure deck, or other surface to improve the surface profile or ride quality before placement of subsequent layers.

Lime Treatment:

The mixing of lime with native or embankment materials to increase the strength of the material which supports the pavement structural section.

Localized Failure:

A pavement that is within a definite locality that exhibits loose and/or spalling pieces of asphalt concrete pavement, brought on by alligator cracking, possibly with rutting and insufficient base support.

Longitudinal Cracking:

Cracks or breaks in flexible or rigid pavements, which are approximately parallel to the pavement center line.

Low-Volume Road:

A roadway generally subjected to low levels of traffic; in the AASHTO Design Guide, structural design is based on a range of 80 kN ESAL’s from 50,000 to 1,000,000 for flexible and rigid pavements, and from 10,000 to 100,000 for aggregate surfaced roads.

Open Graded Asphalt Concrete (OGAC):

An open graded mixture of aggregate and relatively high asphalt content, which provides good skid resistance and a high permeability. OGAC is designed to accommodate rapid surface drainage and minimize the potential of hydroplaning while at the same time providing an effective seal of the underlying asphalt concrete pavement.

Outside Wheel Path (OWP):

The vehicle tire path closest to the outside edge of pavement. Deflection measurements are usually made in the outside wheel path.


An overlay is a layer, usually asphalt concrete, placed on existing asphalt or portland cement concrete pavement to restore ride quality, to increase structural strength (load carrying capacity), and to extend the service life.


Corrections to damaged pavement by adding asphalt concrete. It could be applied to the surface or placed after the distress has been removed.

Pavement Rehabilitation:

Work undertaken to extend the service life of an existing facility. This includes placement of additional surfacing and/or other work necessary to return an existing pavement to a condition of structural or functional adequacy. This might include the partial or complete removal and replacement of portions of the pavement structural section.

Pavement Reinforcing Fabric:

A stress absorbing membrane interlayer that is a nonwoven, bonded fiber, engineering grade synthetic fabric. It is sometimes used by PNPG in asphalt concrete overlays primarily to minimize surface water infiltration and retard reflective cracking through the overlay, from cracks or joints in the existing pavement.


The surface layer of the structural section that carries traffic. Except for special or experimental surface layers, the pavement is either portland cement concrete or asphalt concrete. The asphalt concrete layer may include up to a 30-mm layer of OGAC.

Pot Holes:

Bowl-shaped holes of various sizes in the pavement that generally start when small parts of an alligator-cracked area are dislodged by traffic together with excessive moisture. The depth may be only to the next lift of asphalt concrete or it may extend into the base.

Preventive Maintenance:

Typically, procedures performed to preserve the existing pavement and structural sections utilizing strategies that extend pavement service life.

Prime Coat Prime Coat (Sometimes called tack coat):

The application of a low viscosity liquid bituminous material to existing surface for the purpose promoting adhesion layers during initial construction or overlay.


The ejection of foundation material, either wet or dry, through cracks resulting from vertical movements of the pavement under traffic. This phenomenon is especially pronounced with saturated structural sections.


Gradual degradation of the pavement surface. Weathering or stripping of the asphalt from the aggregates, along with action of the tires, causes separation of the aggregates and asphalt. Stripping may be accomplished by an excessive amount of water with the tire action, or by oil and gas dripping from passing vehicles (drip track raveling). Raveling in the wheel path may also be caused by abrasive chain wear.

Reflective Cracking:

Generally occurs on pavements that have an asphalt concrete surface over jointed portland cement concrete or a cement treated base. This is mainly caused by movement of the PCC or CTB because of thermal and moisture changes.


A supplemental surface layer or replacement layer placed on an existing pavement to restore its riding qualities or to increase its structural (load carrying) strength.

Rigid Pavement:

Primarily portland cement concrete pavement, which distributes the superimposed axle loads over a relatively wide area of underlying structural section layers and soil because of its rigidity and high modulus of elasticity.

Rubberized Asphalt:

A mixture of paving asphalt combined with specified percentages of granulated reclaimed rubber for use as the binder in asphalt concrete and in stress absorbing membrane interlayers (fabric) within or under asphalt concrete overlays. Primary applications where benefits appear to be significant are for providing more resilient and more durable wearing surface for overlays, to retard reflective cracking and overlays on pavement exposed to wear by tire chains. Rubberized asphalt joint sealant is used to keep out incompressible materials and retard surface water infiltration.


Longitudinal depressions that develop in the wheel paths of flexible pavement under traffic. Unstable asphalt concrete pavement or inadequate strength of the underlying foundation most often causes this permanent and sometimes progressive deformation. Rutting may also occur due to chain or studded tire abrasion or raveling.

Seal Coat:

A bituminous coating, with or without aggregate, applied to the surface of a pavement for the purpose of waterproofing, preserving, or rejuvenating a cracked or raveling bituminous surface, or to provide increased skid resistance or resistance to abrasion by traffic.


The ability at time of observation of a pavement to serve traffic (autos and trucks) which use the facility.


Localized vertical displacement of the pavement structural section due to slippage of a fill or consolidation of the underlying foundation, often resulting in pavement cracking and a poor ride quality.


Localized displacement or bulging of pavement in the direction of loading pressure produced by stopping, starting or turning movements. The pavement may have low tensile strength and delamination or may have bleeding from too much asphalt in the mix. Shoving the pavement forward often produces corrugations ahead of the shoving and crescent-shaped cracks behind.

Single Axle Load:

The total load transmitted by all wheels whose centers may be included between two parallel transverse vertical planes extending across the full width of the vehicle.

Slurry Seal:

A mixture of mixing-type asphaltic emulsion, fine mineral aggregate and water proportioned, mixed and spread primarily on asphalt concrete pavement for maintenance purposes.


Cracking, breaking, chipping of the edge of a crack in which small portions of the pavement are dislodged. Spalling is caused primarily by non-uniform support in conjunction with vertical movement due to wheel loads or incompressibles confined in the opening.

Stress Absorbing Membrane Interlayer (SAMI)::

An interlayer placed within or at the bottom of an asphalt concrete overlay or layer to retard reflective cracking and prevent water intrusion. Examples include a rubberized chip seal interlayer (SAMI-R) or pavement reinforcing fabric (SAMI-F).


The loss of the adhesive bond between asphalt cement and aggregate, most often caused by the presence water in asphalt concrete, which may result in raveling, loss of stability and load carrying capacity of the asphalt concrete pavement or treated base.

Structural Section Drainage System:

A drainage system used for both asphalt and portland cement concrete pavements consisting of a treated permeable base layer and a collector system which includes a slotted plastic pipe encapsulated in treated permeable material and a filter fabric barrier with unslotted plastic pipe as vents, outlets and cleanouts to rapidly drain the pavement structural section

Structural Section:

The planned, engineering-designed layers of specified materials (normally consisting of sub base, base, and pavement surface) placed over the basement soil to support the traffic loads anticipated to be accumulated and applied during the design period. The structural section is also commonly called the pavement structural section.

Sub base:

A layer of aggregate of designed thickness and specified quality placed on the basement soils as the foundation for a base.


That portion of the earth on which pavement surfacing, base, sub base or a layer of any other material is placed.

Surface Attrition (“Abrasion”):

Abnormal surface abrasion wears pavement, resulting from either a poor quality surface or exposure to abnormal abrasive action (such as tire chains and sanding materials) or both.

Surface Course:

The top layer of AC pavement. It is also sometimes called the “wearing course”.

Surface Polish:

The loss of the original pavement surface texture due to traffic.

Surface Recycling:

In-place heating of the surface of asphalt concrete pavement followed by scarification, remixing, and compaction, generally to a depth of about 20 mm. This is considered to be a maintenance procedure.

Tack Coat (Paint Binder):

The application of bituminous material to an existing surface to provide bond between the superimposed construction and the existing surface.

Transverse Cracking:

Cracks in asphalt concrete pavement most often created by thermal forces exceeding the tensile strength of the asphalt concrete.

Wearing Course:

See Surface Course


Gradual degradation of the pavement surface. Oxidation and hardening of the asphalt cause separation from the aggregates, along with action of the tires, resulting in surface raveling.