NICET CMT Asphalt key terms

The dark, sticky petroleum product that coats aggregate and holds a mixture together. It is graded by stiffness at specified temperatures and is the component that ages, oxidizes, and controls most mixture behavior.

A binder classification such as PG 64-22, where the first number is the high temperature the binder must resist rutting and the second is the low temperature it must resist cracking, both in degrees Celsius.

The distribution of particle sizes in an aggregate blend, determined by sieving and reported as percent passing each sieve. Gradation controls voids, workability, and the amount of binder a mixture needs.

One sieve size larger than the first sieve that retains more than 10 percent of the aggregate. It sets specimen thickness requirements for compaction testing and is used to label mixture types.

One sieve size larger than the nominal maximum aggregate size. It is the smallest sieve through which 100 percent of the aggregate passes and is used in some specification and volumetric calculations.

A single number describing the average particle size of fine aggregate, computed by summing cumulative percentages retained on a standard sieve series and dividing by 100. Higher values indicate coarser sand.

A test that measures how much clay and fine dust contaminate fine aggregate by comparing sand and flocculated clay heights in a cylinder. Low values signal dirty aggregate and poor mixture durability.

The ratio of an aggregate's mass to the mass of an equal volume of water. Bulk, bulk saturated surface-dry, and apparent values are used to compute voids and asphalt content by mass or volume.

The percentage of water an aggregate absorbs into its permeable pores when soaked, relative to its dry mass. High absorption means binder is absorbed into pores and less is available to coat particles.

The percentage of asphalt binder in a mixture, expressed by total mass or by mass of aggregate. It is measured by ignition oven, extraction, or nuclear gauge and is central to volumetric acceptance.

A test that burns binder off an asphalt sample at high temperature and computes binder content from the mass loss, with a correction for aggregate breakdown and moisture. It is fast but requires calibration.

A mixture-specific value subtracted from the apparent ignition-oven mass loss to account for aggregate mass change during burning. It is established by burning a known sample without binder.

The ratio of a compacted specimen's dry mass to its total volume including permeable voids, determined by weighing the specimen in air and submerged in water. It is the backbone of volumetric analysis.

The specific gravity of a voidless asphalt mixture, measured by vacuuming a loose sample in water. It represents the density the mixture would reach with zero air voids and anchors all volumetric calculations.

The percentage of a compacted mixture's total volume occupied by air, computed from bulk and theoretical maximum specific gravities. It drives durability, permeability, and rutting resistance.

The percentage of a compacted mixture's volume occupied by binder plus air voids, meaning the space between aggregate particles. VMA must be high enough to hold the required binder film.

The percentage of the voids in mineral aggregate that is filled with binder rather than air. It relates to durability and stability and is a required volumetric property for most mixtures.

The ratio of the percentage of aggregate passing the 0.075 mm sieve to the effective asphalt content. Very low or high values indicate mixture problems such as tender or dry mixes.

The portion of total binder that is not absorbed into aggregate pores and therefore coats particles and fills voids. It is computed from total binder content minus absorbed binder.

A laboratory device that compacts asphalt specimens by applying a controlled vertical pressure and a gyrating angle to produce specimens at a target number of gyrations. It is used for volumetric and density acceptance.

A drop hammer used to compact asphalt specimens in a mold for Marshall stability and flow testing. The number of blows per side is specified and affects specimen density.

A test that loads a compacted specimen laterally and records the peak load and deformation at failure. Stability reflects load capacity and flow reflects deformation tolerance.

The density of compacted asphalt in the roadway, expressed as a percentage of a reference density such as laboratory Gmm. It is measured by nuclear gauge or cores and is a primary acceptance property.

In-place density divided by a reference density, multiplied by 100. It is most often referenced to theoretical maximum gravity (Gmm) and compared with a specification minimum.

A field device that estimates in-place density by measuring the attenuation of gamma radiation through the pavement. It is fast but must be calibrated and correlated to cores.

Cutting cylindrical specimens from the finished pavement for laboratory density or thickness measurement. Cores serve as the reference method and are used to calibrate non-nuclear gauges.

A laboratory instrument that measures binder viscosity by rotating a spindle in a heated sample. It is used to check pumping and mixing temperatures and to detect binder grade problems.

An instrument that applies oscillatory shear to binder at controlled temperatures to measure stiffness and elastic response. Results are used to grade binders for rutting and fatigue resistance.

A device that loads a small binder beam at low temperature to measure creep stiffness and creep rate. It is used to assign the low-temperature grade of a performance-graded binder.

An aging procedure that exposes a thin film of binder to heat and air in a rolling jar to simulate aging during mixing and construction. The aged residue is used in further grading tests.

An oven that ages RTFO residue under elevated pressure and temperature to simulate long-term in-service aging. The PAV residue is used for fatigue and low-temperature binder tests.

A dispersion of asphalt binder droplets in water stabilized by an emulsifying agent. It is used for tack coats, fog seals, and cold mixes and breaks as water evaporates.

Asphalt binder thinned with a petroleum solvent so it can be applied at lower temperature. The solvent evaporates after placement, leaving the binder behind.

A thin spray of asphalt material applied to an existing surface to bond it to a new asphalt layer. Adequate coverage and curing are essential to prevent delamination.

Asphalt material applied to a granular base to seal it and promote bond with the asphalt layer above. It penetrates the surface rather than forming a film.

Milled or crushed old asphalt pavement reused in new mixtures as a substitute for virgin aggregate and binder. Its use requires adjustments for aged, stiffer binder and changes in gradation.

Separation of coarse and fine particles during handling, stockpiling, or placement, producing areas of coarse, open-textured pavement. It causes nonuniform density and premature failure.

A mixture that deforms or shoves easily under the roller because of excess fines, excess binder, or rounded aggregate. It resists compaction and can leave a wavy surface.

The tendency of binder to detach from aggregate in the presence of water, causing raveling and loss of strength. It is evaluated by retained strength or boil tests and addressed with antistripping additives.

The ratio of the tensile strength of a moisture-conditioned specimen to that of a dry specimen, expressed as a percentage. Low values indicate moisture susceptibility requiring treatment.