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Glossary of Asphalt Rubber Terms



AASHTO – American Association of State Highway and Transportation Officials

Absolute Viscosity – A measure of the Viscosity of Asphalt Cement with respect to time, measured in poises, conducted at 60°C (140°F). The test method utilizes a partial vacuum to induce flow in the viscometer.

Acceptance – Sampling and testing, or inspection, to determine the degree of compliance with contract requirements for acceptance, rejection, or Pay Adjustment.

Aggregate – Any hard, mineral material such as gravel, crushed stone, sand, Slag, etc.

Aggregate Storage Bins or Cold Feed Bins – Bins that store the necessary Aggregate sizes and feed them to the Dryer in a Hot Mix Plant in substantially the same proportions as are required in the finished mix.

Air Voids – The amount of air in a compacted Asphalt Concrete mixture, expressed as a percentage of the total volume of the mixture.

Alligator Cracking – The occurrence of 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.

Ambient Grinding – A grinding method for processing scrap tires into crumb rubber by passing the tires through a series of grinders at ambient temperatures. Ambient Grinding produces crumb rubber particles with a very rough, sandpapery surface texture.

Anti-oxidant – Any material that slows the oxidation reaction (aging).

Asphalt – See Asphalt Cement.

Asphalt Binder – Asphalt Cement used in paving applications that has been classified according to the Standard Specification for Performance Graded Asphalt Binder, AASHTO Designation MP1. It can be either unmodified or modified Asphalt Cement, as long as it complies with the specifications.

Asphalt Cement or Asphalt – A dark brown to black cementitious material in which the predominating constituents are Bitumens, which occur in nature or are obtained in petroleum processing. Asphalt Cement is a constituent in varying proportions of most crude petroleum and is used for paving, roofing, industrial and other special purposes. It is a semi-solid at room temperature and a liquid at hotter temperatures.

Asphalt Concrete - A mixture of Asphalt Binder and Aggregate used as a paving material, which is thoroughly mixed and compacted to form a pavement layer.

Asphalt Concrete Overlay - One or more courses of Asphalt Concrete placed over an existing pavement.

Asphalt Content – The amount of Asphalt Binder in an Asphalt Concrete mixture, expressed as a percentage of the weight of the total mix (Coarse Aggregate, Fine Aggregate, Asphalt Binder, Mineral Filler, lime, fibers, etc.).


Asphalt Emulsion - An emulsion of Asphalt Binder, water, and a small amount of an Emulsifying Agent (soap) to give it a liquid consistency at ambient temperatures so that it can be sprayed on a road surface. Once the water begins to evaporate, the Asphalt Emulsion “breaks”, leaving the sticky Residual Asphalt Binder behind. Emulsified Asphalt Binder droplets may have a positive surface charge, a negative surface charge, or no surface charge (neutral).

Asphalt Mat – The term used to refer to the Asphalt Concrete layer when it is still hot during placement and Compaction operations.

Asphalt Primer – Low-Viscosity (highly liquid) Asphalt Cement, which penetrates into a non-Bituminous (like crushed stone) surface upon application.

Asphalt Rubber Blending Unit – See Portable Blending Unit.

ARTS – Asphalt Rubber Technology Service

ASTM – American Society of Testing and Materials

Axial Stress – Pressure resulting from the application of force along the object’s central axis.

Base Course - The layer in the Pavement Structure immediately below the Surface and/or Intermediate Courses and immediately above the Subgrade and/or Subbase Course. It usually consists of crushed stone, although it may consist of crushed slag or other stabilized or un-stabilized material.

Batch Plant – A type of Hot Mix Plant that manufactures HMA in batches rather than continuously and is more suited for small manufacturing runs and (frequent) changes in mixture types.

Bending Beam Rheometer (BBR) – A piece of laboratory equipment used in the AASHTO TP1 procedure to evaluate Asphalt Binder properties at low pavement temperatures by measuring how much a binder Deflects, or creeps, under a constant load at a constant temperature. This test provides insight into a binder’s resistance to thermal, or low-temperature, cracking. The BBR test temperatures are related to a pavement’s lowest service temperature, and when its results are used in conjunction with results from the DSR, it can provide the stiffness behavior for Asphalt Binder over a wide range of temperatures.

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.

Bleeding or Flushing - The upward migration of Asphalt Binder in an Asphalt Concrete pavement resulting in the formation of an Asphalt Binder film on the pavement surface.

Brittle – Describes a material with the tendency to fracture (break) without much stretching.

Breaking - The phenomenon when Asphalt Binder and water separate in an Asphalt Emulsion beginning the Curing process. The rate of Breaking is controlled primarily by the Emulsifying Agent, although it is also somewhat dependent on environmental conditions.

Bulk Specific Gravity (BSG or Gmb) – In the context of Asphalt Concrete mixtures, the Specific Gravity of a compacted sample from the mix design or the finished pavement.

Coarse Aggregate - Aggregate mostly retained on the 4.75 mm (No. 4) Sieve.

Compaction – The act of increasing the Density of HMA by applying a specific amount of loading. In the lab, this is done with a Marshall hammer or a Superpave Gyratory Compactor. In the field (during construction of the pavement), this is done with various combinations of Steel-wheel and Rubber-tired Rollers.

Complex Shear Modulus (G*) – A measure of the total resistance of a material (in this case, Asphalt Binder) to Deformation when exposed to repeated pulses of Shear Stress. It consists of a recoverable (elastic) component and a non-recoverable (viscous) component. For Asphalt Binder, this is highly dependent upon the temperature and frequency of loading.

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.

Corrugation or Shoving - A form of permanent Deformation typified by ripples across the pavement surface. These Distortions usually occur at points where traffic starts and stops, on hills where vehicles break on the downgrade, on sharp curves, or where vehicles hit a bump and bounce up and down.

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

Creep - Gradual Deflection under a constant load applied at a constant rate. With respect to the Bending Beam Rheometer test for Asphalt Binder, Creep loading simulates the thermal stresses that gradually build up in a pavement when temperature drops.

Crumb Rubber Modifier (CRM) - The term used to describe ground waste tire rubber used in Hot Mix Asphalt and other paving applications.

Crusher-Run - The unscreened raw product of a stone crusher.

Cryogenic Grinding – A grinding method for processing scrap tires into crumb rubber by freezing the tires with liquid nitrogen and then passing them through hammer mills where they are shattered into small particles. Cryogenic Grinding produces crumb rubber particles with a very smooth, glasslike surface texture.

Curing – In reference to an Asphalt Emulsion, it is the development of the mechanical properties of the Asphalt Binder after the Asphalt Emulsion has “broken” and the Residual Asphalt Binder bonds to the underlying HMA surface and the cover Aggregate or the Asphalt Concrete Overlay. In reference to PCC, it is the development of rigidity resulting from the hydration reaction occurring in the Portland Cement paste.

Cutback Asphalt - Asphalt Binder that has been liquified by blending with petroleum solvents (diluents). Upon exposure to atmospheric conditions, the diluents evaporate, leaving behind the Residual Asphalt Binder to perform its function. Cutback Asphalts are rarely used anymore because they are not environmentally-friendly.

Deflection - A load-induced, downward movement of a pavement section.

Deformation – See Distortion

Delta – See Phase Angle

Dense-graded HMA – HMA made with a Dense-graded aggregate blend. Dense-graded aggregate has approximately equal proportions of Coarse, medium-sized, and Fine Aggregate particles that can fit closely together when compacted. Although it is possible for Dense-graded HMA to have the same percentage of air voids as Gap-graded HMA, the distribution of voids is very different. Dense-graded HMA has many small voids, while Gap-graded HMA has a few large voids.

Density – The ratio of a substance’s weight compared to its volume (weight per unit volume), often expressed in pounds-per-cubic-foot (pcf) or grams-per-cubic-centimeter (g/cc). In the context of Asphalt Concrete pavement, Density is increased by reducing the amount of air in the pavement layer through Compaction processes.

Design ESAL - The total number of Equivalent 80-kN (18,000-lb.) Single Axle Load (ESAL) applications expected throughout the Design Period.

Design Lane - The lane on which the greatest number of Equivalent 80-kN (18,000-lb.) Single Axle Loads (ESAL) is expected. This will normally be either lane of a two-lane roadway or the outside lane of a multi-lane highway.

Design Period - The number of years from the initial application of traffic until the first planned major resurfacing or overlay. This term should not be confused with pavement life or analysis period. Adding Asphalt Concrete Overlays as required will extend pavement life indefinitely or until geometric considerations (or other factors) make the pavement obsolete.

Direct Tension Tester (DTT) - A piece of laboratory equipment used in the AASHTO TP3 procedure to discover an Asphalt Binder’s ability to stretch before breaking. The DTT procedure is performed at very low temperatures, where binders generally exhibit Brittle rather than Ductile behavior. In addition, the binders tested are aged with both the RTFO and the PAV, which also increase Brittle tendencies. The DTT measures the amount of elongation per unit length (strain) exhibited by a “dog bone” shaped (wide on each end and narrow in the middle) Asphalt Binder specimen before breaking (failure). Like the BBR, the DTT also provides insight into a binder’s ability to resist thermal (low-temperature) cracking.

Disintegration - The breaking up of a pavement into small, loose fragments caused by traffic or weathering.

Distortion or Deformation – Any change of a pavement surface from its original shape.

Drum Mix Plant - A type of Hot Mix Plant that proportions the aggregate, then dries and coats the Aggregate with a proportional amount of Asphalt Binder in the same drum. Drum Mix Plants produce HMA continuously rather than in batches and are more suited for long runs of the same product.

Dryer - An apparatus that will dry the Aggregates and heat them to the specified temperatures.

Ductility - The ability of a substance to be drawn out or stretched thin without breaking. 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.

Durability - The property of an Asphalt Concrete pavement that represents its ability to resist Disintegration by weathering and traffic.

Dynamic Shear Rheometer (DSR) – A piece of laboratory equipment used to perform the AASHTO TP5 procedure on un-aged, RTFO-aged, and PAV-aged Asphalt Binders. In the DSR, a small disc-shaped sample of Asphalt Binder is sandwiched between two plates, one of which is fixed, and the other of which is oscillating. The DSR measures the Complex Shear Modulus and Phase Angle at intermediate and high temperatures, which can be used to predict resistance to Rutting and Fatigue Cracking in Asphalt Concrete pavements made with the Asphalt Binder being tested.

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.

Emulsified – (See Asphalt Emulsion and Emulsifying Agent or Emulsifier)

Emulsifying Agent or Emulsifier - The chemical added to the water and Asphalt Binder that keeps the droplets of Asphalt Binder in stable suspension in the water. The Emulsifier determines the charge of the Asphalt Emulsion and controls the Breaking rate.

Equivalent Single Axle Load (ESAL) - The effect on pavement performance of any combination of axle loads of varying magnitude equated to the number of 80-kN (18,000-lb.) single-axle loads that are required to produce an equivalent effect.

Fatigue Cracking – A Crack caused by repeated flexure.

Fatigue Resistance - The ability of asphalt pavement to resist Crack initiation caused by repeated flexing (Fatigue Cracking).

Fault - A difference in elevation of two PCC slabs at a joint or Crack.

FHWA – Federal Highway Administration (United States of America)

Fine Aggregate - Aggregate entirely passing the 4.75 mm (No. 4) Sieve and mostly retained on the 75um (No. 200) Sieve.

Flexibility - The ability of a pavement to conform to settlement of the foundation without fracturing. Generally, high Asphalt Binder content or the use of Rubber-modified Asphalt Binder enhances the flexibility of Asphalt paving mixtures.

Fog Seal - A light application of diluted Asphalt Emulsion. It is used to renew old asphalt pavement surfaces, seal small cracks and surface voids, and inhibit Raveling.

Full-depth Asphalt Pavement – A Pavement Structure that is designed and constructed so that all courses above the Subgrade are Asphalt Concrete. A Full-Depth Asphalt Pavement is placed directly on the prepared Subgrade.

G* - See Complex Shear Modulus

Gap-graded HMA – HMA made with a gap-graded aggregate blend. Gap-graded aggregate has large proportions of Coarse and Fine Aggregate particles, but a very small proportion of medium-sized Aggregate particles. This particle-size distribution exhibits a great deal of stone-on-stone contact between the Coarse Aggregate particles. Although it is possible for Gap-graded HMA to have the same percentage of air voids as Dense-graded HMA, the distribution of voids is very different. Gap-graded HMA has a few large voids, while dense-graded HMA has many small voids.

Gyratory Compactor – A type of lab compactor used in the Superpave method of HMA mix design or for compacting samples of hot mix asphalt into specimens used for volumetric analysis for Quality Control activities at the Hot Mix Plant. It compacts samples of HMA with a kneading motion caused by a set pressure and angle of gyration while continuously recording sample height measurements.

Hot Aggregate Storage Bins - Bins that store heated and fractionated Aggregates prior to their final proportioning into the Hot Mix Plant.

Hot Mix Asphalt (HMA) - A form of Asphalt Concrete that is mixed at a contractor’s Hot Mix Plant, transported to the roadway in dump trucks, placed using a paver, and compacted with Steel-wheel or Rubber-tired Rollers.

Hot Mix Plant or Hot Mix Asphalt (HMA) Plant – A manufacturing facility that produces Asphalt paving mixtures by heating the ingredients (Aggregate, Hydrated Lime, Asphalt Binder, and sometimes other modifiers), combining them in the correct proportions, and blending them to form a homogeneous mixture. It can be either a Batch Plant or a Drum Plant.

Indirect Tensile Strength (ITS) – Test procedure to examine Asphalt Concrete mixtures for Moisture Susceptibility. The ITS value is measured on both dry samples and samples that have been exposed to heat and moisture. The “dry” and “wet” ITS values are then used to calculate the TSR.

Intermediate Course – The layer in the Asphalt Concrete Pavement Structure immediately below the Surface Course, generally consisting of larger Aggregates and less Asphalt Binder (by weight) than the Surface Course.

Kinematic Viscosity - A measure of the Viscosity of Asphalt Cement, measured in centistokes, conducted at a temperature of 135°C (275°F).

Lane Joint Cracks - Longitudinal separations along the seam between two paving lanes.

Lift - A layer or course of paving material applied to a base or a previous layer.

Load Equivalency Factor - The number of 80-kN (18,000-lb.) single-axle load applications (ESAL) contributed by one passage of an axle.

Longitudinal Crack - A vertical Crack in the pavement that is approximately parallel to the centerline of the pavement.

Maximum Specific Gravity (MSG or Gmm) – The Specific Gravity of an Asphalt Concrete mixture when that mixture has zero Air Voids (i.e., it is in the condition of maximum Density).

Mesh – The square openings present on the surface of a Sieve. Sieve size is defined by the number of Mesh openings per linear inch of the Sieve surface. For example, a No. 40 Mesh sieve has 40 openings per linear inch of Sieve surface.

Milling Machine - A self-propelled unit having a cutting head equipped with carbide-tipped tools for the pulverization and removal of layers of Asphalt paving materials from pavements. If this removed material is reused in a new pavement, it is called RAP.

Mineral Dust - The portion of the Fine Aggregate passing the 0.075 mm (No. 200) Sieve.

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.

Moisture Susceptibility – Refers to susceptibility of an Asphalt Concrete mixture to Stripping. This property is tested during mix design with the ITS test procedure.

Multiple Surface Treatment - Two or more surface treatments placed one on the other. The Aggregate maximum size of each successive treatment is usually one-half the previous one. A Multiple Surface Treatment may be a series of Single Surface Treatments that produces a pavement course up to 25mm (1 in.) or more in thickness. A Multiple Surface Treatment is a denser waterproofing and Wearing Course than a Single Surface Treatment.

Natural 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.

Non-Destructive Testing (NDT) – Testing methods usually performed on in-place construction materials that do not cause any damage to the materials being tested. In the context of pavement evaluation, NDT is Deflection testing, without destruction to the pavement, to determine a pavement's response to pavement loading.

Open-graded Friction Course (OGFC) - A pavement Surface Course that consists of a high-void, Asphalt Concrete mix that permits rapid drainage of rainwater through the course and off the shoulder of the road. The mixture consists of either Polymer-modified or Rubber-modified Asphalt Binder, a large percentage of one-sized coarse Aggregate, and a small amount of fibers. OGFC prevents tires from hydroplaning and provides a skid-resistant pavement surface with significant noise reduction.

Pavement Structure - The entire pavement system of selected materials from Subgrade to the Surface Course.

Pay Adjustment – The actual amount, either in dollars or in dollars per area/weight/volume, that is to be added or subtracted to the contractor’s bid price or unit bid price.

Performance-Graded (PG) - Asphalt Binder grade designation used in Superpave. It is based on the binder's mechanical performance at critical temperatures and aging conditions.

Permeability – A measure of the ability of a pavement to allow the passage of air and water into or through the pavement.

Phase Angle (delta) – Indicator of the relative amounts of recoverable (elastic) and non-recoverable (viscous) Deformation in a material when it is exposed to repeated pulses of Shear Stress. For Asphalt Binder, this is highly dependent upon the temperature and frequency of loading.

Plant Mix (Cold) - A mixture of Emulsified (or Cutback) Asphalt Cement and unheated mineral Aggregate prepared in a central mixing plant and spread and compacted with conventional paving equipment while the mixture is at or near ambient temperature.

Plant Screens - Screens located between the Dryer and the Hot Aggregate Storage Bins, which separate heated Aggregates into proper hot bin sizes.

Polished Aggregate - Aggregate particles in a pavement surface that have been worn smooth by traffic.

Polymer – With respect to Asphalt, a Polymer is any substance added to Asphalt to enhance its properties. In general, a Polymer is a material with a long-chained molecular structure, including natural rubber, synthetic rubber, plastics, etc.

Polymer-modified Asphalt Binder – Asphalt Binder that has been blended with a Polymer like styrene-butadiene block copolymer (SBS). It has improved properties and a higher PG-Grading compared to conventional Asphalt Binder. In South Carolina, the SC DOT specifies PG 64-22 for conventional Asphalt Binder and PG 76-22 for Polymer-modified Asphalt Binder.

Portable Blending Unit or Asphalt Rubber Blending Unit – The piece of equipment used to blend CRM and Asphalt Binder to produce Rubber-modified Asphalt Binder at the HMA Plant. It connects directly to the plant and requires little or no modifications to the plant.

Portland Cement – A gray, powdery material that meets ASTM Standard C 150 and is composed primarily of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. When combined with water, Portland Cement reacts with the water to form a paste, which then becomes rigid as the reaction between the cement and water progresses.

Portland Cement Concrete (PCC) – A mixture of Portland Cement, Aggregate, water, and other admixtures that is placed in forms and becomes rigid as it cures. It is a commonly used construction material in both highway and building construction.

Potholes - Bowl-shaped openings in the pavement resulting from localized
Disintegration.

Present Serviceability - The ability of a specific section of pavement to serve its intended use in its existing condition.

Pressure Aging Vessel (PAV) – A piece of laboratory equipment used to perform AASHTO PP1 procedure on samples of Asphalt Binder after they have been aged in the RTFO. The PAV further ages these binder samples by exposing them to high pressure and temperature for 20 hours to simulate the effects of long-term aging. PAV-aged binders are tested with the DSR, the BBR, and the DTT.

Prime Coat - An application of Asphalt Primer to an absorbent surface. It is used to prepare an untreated Base Course for a Surface Course of Asphalt Concrete. The Asphalt Primer penetrates or is mixed into the surface of the Base Course and plugs the voids, hardens the top, and helps bind it to the overlying Asphalt Concrete Surface Course.

Pumping – PCC slab Deflection under passing loads, eventually resulting in the discharge of water and Subgrade soils along joints, Cracks, and pavement edges.

Quality Assurance (QA) – All those planned and systematic actions necessary to provide confidence that a product or facility will perform satisfactorily in service. Quality Assurance includes Quality Control.

Quality Control (QC) or Process Control – Those Quality Assurance actions and considerations necessary to assess and adjust production and construction processes so as to control the level of quality being produced in the end product. This is separate from Acceptance testing, but it is a part of Quality Assurance.

Raveling - The progressive separation of Aggregate particles in a pavement from the surface downward or from the edges inward.

Rebound Deflection - The amount of surface rebound when a load is removed.

Reclaimed Asphalt Pavement (RAP) – RAP is excavated Asphalt Concrete pavement that has been pulverized, usually by milling, and is reused in the production of new Asphalt Concrete paving mixtures.

Reflection Cracks or Reflective Cracking - Cracks in Asphalt paving overlays (usually over deteriorated PCC pavements) that reflect the Crack pattern in the Pavement Structure below the overlay.

Residual Asphalt Binder - The Asphalt Binder that remains from an Asphalt Emulsion after the Emulsifying Agent has broken and cured, or the remains of a Cutback after the volatiles have cured.

Residual Deflection - The difference between original and final elevations of the pavement surface resulting from the application to, and removal of, one or more loads from the surface.

Resiliency – The ability of a material to resist non-recoverable Deformation under repeated loading.

Resilient Modulus of Elasticity - A laboratory measurement of the behavior of pavement materials to characterize their stiffness and Resiliency. A confined or unconfined test specimen (core or re-compacted) is repeatedly loaded and unloaded at a prescribed rate. The resilient modulus is a function of load duration, load frequency, and number of loading cycles.

Resistance (R-Value) - A test for evaluating Bases, Subbases, and Subgrades for pavement thickness design.

Rolling Thin Film Oven (RTFO) – A piece of laboratory equipment used to perform AASHTO T240 or ASTM D 2872 procedures to simulate aging in Asphalt Binder samples representative of the aging that occurs during mixing and construction of HMA pavement. The RTFO procedure can be done to provide samples for use in further testing or to determine the mass lost (from lost volatiles) or gained (from the formation of oxidation reaction products) by the binder samples during the aging process. The RTFO ages binder samples by continually exposing them to heat and air flow to promote an oxidation reaction. This reaction is an accelerated version of the aging occurring naturally in Asphalt Binders in pavements. RTFO-aged binders may be tested with the DSR or aged further with the PAV.

Rotational Viscometer – A piece of laboratory equipment used to measure the Viscosity of un-aged modified and unmodified Asphalt Binders using the ASTM D4402 procedure. This test may be performed at a variety of test temperatures to gain insight into the Workability of Asphalt Concrete mixtures containing that particular Asphalt Binder or to develop Temperature-Viscosity Charts for the binder being tested.

Roughometer - An instrumented, single-wheel trailer, which measures the roughness of a pavement surface in accumulated millimeters, or inches, per mile.

Rubber-modified Asphalt Binder or Asphalt Rubber Binder – Asphalt Binder that has been blended with CRM made from ground scrap tires at an elevated temperature to “react” the rubber with the binder. It may be blended on-site at the contractor’s HMA plant or terminally at the Asphalt Binder supplier’s terminal, and it may be used in a variety of pavement applications, including Dense-graded HMA, Gap-graded HMA, OGFC, SAM, SAMI, and Crack-sealant. Rubber-modified Asphalt Binder used in different applications may contain different amounts of CRM.

Rubber-modified Asphalt Concrete or Rubber-modified HMA or Asphalt Rubber Asphalt Concrete – HMA that is made with Rubber-modified Asphalt Binder. Rubber-modified Asphalt Concrete is produced using the Wet Process.

Rubber-tired Roller or Pneumatic-tired Roller - A compactor used to compact various types of Asphalt pavements with a number of rubber tires spaced so that their tracks overlap, delivering a kneading type of Compaction.

Rubberized Asphalt – A broad term to describe HMA that contains CRM made from recycled rubber. This CRM can be introduced into the HMA by using either the Wet Process or the Dry Process. All ARTS projects use the Wet Process.

Rubbilization - The pulverization of a PCC pavement into smaller particles, reducing the existing pavement layer to a sound, structural base that will be compatible to an Asphalt Concrete Overlay.

Rutting - Channelized depressions that develop in the wheel tracks of Asphalt pavements resulting from consolidation under traffic loading in one or more of the underlying pavement layers. Rutting is not a surface problem, and usually begins in the lowest pavement layer. It is a structural problem of insufficient pavement strength caused by either insufficient design pavement thickness or the weakening of an underlying pavement layer due to moisture damage.

Sand - Fine Aggregate resulting from natural disintegration and abrasion of rock.

Sandwich Seal - A surface treatment consisting of the application of large Aggregate, followed by a spray-applied Asphalt Emulsion, and covered with smaller Aggregate.

Scaling - The peeling away or disintegrating of the surface of PCC.

SC DOT – South Carolina Department of Transportation

Screenings - Fine Aggregate resulting from the rock-crushing process.

Seal Coat – A thin surface treatment used to improve the surface texture and protect an Asphalt pavement surface.

Shear Stress – the Stress resulting from the application of forces parallel to each other, but in opposite directions. A Shear failure is one in which the material rips or tears as a result of the applied Shear Stress.

Shrinkage Cracks - Interconnected Cracks forming a series of large blocks, usually with sharp corners or angles.

Sieve - An apparatus for laboratory work, which has a bottom made of mesh with square openings for catching a specific size of material. Multiple Sieves are used together to separate material into various sizes.

Single Surface Treatment - A single application of liquefied Asphalt to a road surface, followed immediately by a single layer of Aggregate. The thickness of the treatment is about the same as the nominal maximum size Aggregate particle used.

Skid Resistance - The ability of a paved surface, particularly when wet, to offer resistance to slipping or skidding. Proper Asphalt Content, the use of Rubber-modified Asphalt Binder, and the use of Aggregate with a rough surface texture and high resistance to Polishing are the greatest contributors to high Skid Resistance.

Slag - The nonmetallic material, consisting essentially of silicates and alumino-silicates of lime and other compounds, that is developed simultaneously with iron in a blast furnace. It is a byproduct of the iron manufacturing process.

Slippage Cracks - Crescent-shaped openings in the pavement surface resulting from traffic-induced horizontal forces that are open in the direction of the thrust of wheels on the pavement surface. They result when severe or repeated Shear Stresses are applied to the surface and there is a lack of bond between the surface layer and the course beneath. This lack of bond can be caused by the use of insufficient amounts of Prime or Tack, or the application of Prime or Tack to a dirty or wet pavement surface.

Slurry Seal - A mixture of Asphalt Emulsion, well-graded Fine Aggregate, Mineral Filler or other additives, and water. A Slurry Seal will fill minor Cracks, restore a uniform surface texture, and restore friction values.

Source Properties - Aggregate characteristics that must follow certain criteria to satisfy a Superpave mix design. Specified values are established by local agencies. They include Toughness, Soundness, and Deleterious Materials.

Spalling - The breaking or chipping of a PCC pavement at joints, Cracks, or edges, usually resulting in fragments with featheredges.

Specific Gravity – The ratio of the weight of a substance compared to the weight of water when the volume of the substance and the volume of water are exactly equal (i.e., the Density of a substance compared to the Density of water).

Stability - The ability of an Asphalt Concrete mixture to resist Deformation from imposed loads. Stability is dependent upon both internal friction and cohesion.

Steel-wheel Static Roller – Tandem or three-wheel roller with cylindrical steel drums that apply their weight directly to the pavement.

Steel-wheel Vibratory Roller - A roller having single or double cylindrical steel drums that perform Compaction of pavements with weight and vibration. The amount of compactive force is adjusted by changing the frequency and amplitude of vibration.

Strain – Total change in dimension divided by the original dimension.

Stress – Pressure (force per unit area) resulting from the application of force.

Stripping – The breaking of the bond between Asphalt Binder and Aggregate in an Asphalt Concrete mixture due to the penetration of water between the Asphalt Binder and Aggregate. Moisture Susceptible mixes exhibit this phenomenon.

Structural Overlay - An Asphalt Concrete Overlay constructed for the purpose of increasing the structural value and ride quality of the Pavement Structure.

Subbase - The course in the Pavement Structure immediately below the Base Course. If the Subgrade soil has adequate support, it may serve as the Subbase.

Subgrade - The soil prepared to support a Pavement Structure or system. It is the foundation of the Pavement Structure.

Subgrade Resilient Modulus - The modulus of the Subgrade determined by repeated load, triaxial compression tests on soil samples. It is the ratio of acceptable Axial Stress (pressure from forces applied perpendicular to the top and bottom surfaces of the sample) compared to recoverable axial Strain (recoverable Deformation per unit length, measured in the direction parallel to its vertical axis).

Superpave – Short for "Superior Performing Asphalt Pavement", a performance-based system for selecting and specifying Asphalt Binders and for designing HMA mixtures that utilizes a Gyratory Compactor for Compaction of laboratory specimens (“pills”). It integrates the selection of materials (Asphalt Binder and Aggregate) and Volumetric proportioning with the project's climate and design traffic loading.

Surface Course – The top layer of an Asphalt Concrete Pavement Structure.

Tack Coat - A relatively thin application of Asphalt Binder applied to an existing Asphalt Concrete or PCC surface at a prescribed rate. Asphalt Emulsion is the preferred type. It is used to form a bond between an existing surface and the overlying Asphalt Concrete course.

Temperature Segregation or Temperature Differential – The existence of isolated areas of varying temperatures in the Asphalt Mat during placement and Compaction. These “hot spots” and “cold spots” will exhibit different Density values than the surrounding pavement after Compaction.

Temperature/Viscosity Chart – A chart plotting temperature versus Viscosity for a particular Asphalt Binder to be utilized in the estimation of mixing and Compaction temperatures for use in HMA mix design.

Tensile Strength Ratio (TSR) – TSR is the ratio between the “wet” ITS value and the “dry” ITS value for an Asphalt Concrete mixture, expressed in percent form. A low TSR value (below 85% for SC DOT specifications) means that the mix lost a relatively large amount of strength when exposed to heat and moisture, and it can probably be considered a Moisture Susceptible mix.

Transverse Crack - A Crack that follows a course approximately perpendicular to the centerline of the pavement.

Truck Factor - The number of ESALs contributed by one passage of a vehicle. Truck Factors can apply to vehicles of a single type or class or to a group of vehicles of different types.

Upheaval - The localized upward displacement of a pavement due to swelling of the Subgrade or some portion of the Pavement Structure.

Viscosity – A measure of a fluid’s resistance to flow with respect to time. The slower a fluid flows, the higher the Viscosity. For example, molasses has a much higher Viscosity than water.

Viscosity-Graded - A classification system of Asphalt Cements based on Viscosity ranges at 60°C (140°F). A minimum viscosity at 135°C (275°F) is also usually specified. The purpose is to prescribe limiting values of consistency at these two temperatures. 60°C (140°F) approximates the maximum temperature of a HMA pavement surface in service in the U.S. 135°C (275°F) approximates the mixing and laydown temperatures for HMA pavements.

Voids Filled with Asphalt (VFA) - With respect to Asphalt Concrete mixtures, the amount of Asphalt Binder, expressed as a percentage of the VMA.

Voids in the Mineral Aggregate (VMA) – With respect to Asphalt Concrete mixtures, the amount of Air Voids and Asphalt Binder, expressed as a percentage of the total mixture volume.

Volumetric Properties – In the context of Asphalt Concrete mixtures, it refers to properties relating to mixture volume, like Air Voids, VMA, VFA, MSG, and BSG.

Wearing Course – The uppermost pavement layer forming the surface of the pavement that is exposed to traffic and environmental conditions. This may be a Surface Course of Asphalt Concrete, SAM, SAMI, or any other type of surface treatment.

Well-graded Aggregate - Aggregate graded with relatively uniform proportions, from the maximum size all the way down to dust.

Wet Grinding – A grinding method for processing scrap tires into extremely fine crumb rubber by first using Ambient or Cryogenic Grinding and then adding water to form a water/rubber slurry, which is passed through closely-spaced grinding stones. Wet Grinding produces very fine, powdery crumb rubber particles.

Workability - The ease with which paving mixtures may be placed and compacted.


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