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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-98-085

LTPP Guide to Asphalt Temperature Prediction and Correction


see asphaltic concrete


A dark brown to black cementitious material in which the predominant constituents are bitumens, which occur in nature or are obtained in petroleum processing. Asphalt is a constituent in varying proportions of most crude petroleum and used for paving, roofing, industrial and other special purposes.

Asphaltic concrete

A mixture of asphalt binder and aggregate thoroughly mixed and compacted into a mass.


In the field of pavement engineering, the term backcalculation is used to refer to the process of determining the elastic moduli of layers in a layered system based on surface deformations due to applications of known loads. There are several different techniques in common usage, but they all involve comparing surface deformations calculated using estimated layer moduli to the measured deformations. Datasets used in backcalculation are generally generated by falling weight deflectometers and dynamic deflectometers.


A material used to cement loose materials together. The resulting material is generally referred to as a concrete, as in Asphaltic Concrete.



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.


A material that contains or is impregnated with bitumen.

Dynamic deflectometer

A device that measures the deformation response of a pavement due to a sinusoidal load generated by an oscillating mass. Common types of dynamic deflectometer include the Dynaflect and the Road Rater. Dynamic deflectometers have been superseded by falling weight deflectometers in many organizations.

Dynamic modulus

Generally, Dynamic Modulus is defined as a modulus calculated under non static loading conditions. In the context of pavement materials, Dynamic modulus is more narrowly defined as the value of peak-to-peak stress divided by peak-to-peak strain of a material under sinusoidal loading at a given frequency of loading.

Falling weight deflectometer

A device that measures the deformation response of a pavement due to a load generated by the arrest of a falling mass. For more information, please see the FAQ entry.


See falling weight deflectometer

Hydraulic cement

A cement that depends on a chemical reaction with water to produce a bond. The most common type of hydraulic cement is Portland cement.


The lagging of an effect behind its cause. For pavement materials, the term hysteresis is more specifically used to refer to the lagging of peak deformation behind peak load under cyclic loading. This lag is also known as a "phase-shift", and is due to inertial and visco-elastic effects.

Long Term Pavement Performance

Commonly known by its acronym, LTPP, the Long Term Pavement Performance program is an extensive research project that is investigating the factors that affect the performance of pavements throughout the United States and Canada. For more information, please see the LTPP homepage.


See long term pavement performance.

Mechanistic-empirical design

A design method which includes both fundamental engineering properties of pavement materials and empirical "calibration factors" as inputs. The calibration factors are meant to account for localized or otherwise difficult to model minor effects.

Resilient modulus

Stiffness of a material under cyclic loading calculated using only recoverable strain. In the field of pavement materials, the loading waveform used is generally "haversine" to better simulate actual wheel loading. LTPP has developed laboratory testing protocols for determining the resilient modulus of unbound materials and asphalt materials.


A subjective measure of a pavement's smoothness

Seasonal monitoring program

A sub-program within LTPP, the seasonal monitoring program, or SMP studies seasonal effects on pavements through multiple rounds of FWD testing over the course of a year. SMP sites also include on-site automated weather stations (AWS), and permanently installed thermistors and time-domain reflectometry (TDR) equipment at multiple depths in the pavement structure.


See seasonal monitoring program

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