Cracking in asphalt concrete pavements is a major form of pavement distress in the United States. Because the cracking phenomenon is complex and cracking is often affected by both material and structural factors, field engineers have no quick and effective test and analysis protocols. A suite of fatigue analysis tools—as well as applications built around the simplified viscoelastic continuum damage (S-VECD) model—is presented. The S-VECD formulation is presented in a summarized form. Next, the characterization protocols, which are consistent with the capabilities of the asphalt mixture performance tester, are shown. Considerable attention is then given to S-VECD–based analysis tools for assessment of material- and pavement-level fatigue performance. Results show that the S-VECD model can be used to predict the number of cycles until fatigue failure for both constant stress and constant strain loading. The S-VECD model's sensitivity to mixture composition and external factors is shown through predictions of the endurance limit. Finally, pavement performance predictions are used to show how the S-VECD model can predict the field performance results of full-scale accelerated pavement tests, quantify the expected performance of pavement design alternatives, and identify factors that affect top-down cracking.

The Viscoelastic Continuum Damage (VECD) model has been implemented into a finite element package (FEP++) to predict the fatigue performance of asphalt concrete (AC) mixtures tested at the Federal Highway Administration Accelerated Load Facility (FHWA ALF) and the Korea Expressway Corporation (KEC) test road project sites. Both the VECD model and the FEP++ were developed at North Carolina State University. The conceptual approach taken for this research is to separate the characteristics of the pavement system that are related to the material from those related to the boundary conditions. It is believed that this study is the first application of an integrated structural/material mechanistic model for the fatigue performance prediction of AC pavements where damage in the asphalt layers is considered for the full time history and where the change in stiffness due to damage evolution is captured in the subsequent calculation of damage. The VECD model accounts for the viscoelastic nature of AC mixtures with growing damage, whereas the finite element model accounts for other important characteristics, such as temperature, layer thickness, stiffness gradient, etc. The controlled FHWA ALF experiment allows a direct comparison between observed and modeled fatigue performance. Because the KEC test road experiment is subjected to real and variable traffic and environmental factors, the finite element simulation results are used to examine the effects of specific parameters in the pavement system on fatigue performance. In this regard, the model is found to effectively capture the effects of changes in layer thickness, layer material, and layer type. The need to develop transfer functions for true field performance prediction is also shown, and a simple example function is developed as proof of this concept.

Aging has long been recognized as a contributing factor to fatigue distress of asphalt concrete pavement. Several research studies have been undertaken to gain fundamental understanding of the aging phenomenon at the asphalt binder level. However, relatively little effort has been made to understand and to quantify the effects of aging on fundamental characteristics of asphalt mixtures. The effects of oxidative aging on the dynamic modulus and the fatigue performance of asphalt mixtures is examined. For this purpose, an asphalt mixture is aged in the laboratory at four aging levels. Mechanical tests for the four aged mixtures are performed to characterize the linear viscoelastic and damage properties. Such characterization is investigated to incorporate the aging effects into a more comprehensive analytical framework for predicting the performance of asphalt concrete pavements. Finally, this framework is used to evaluate the aging effects on an example asphalt concrete pavement. It is found that aging can significantly change the performance of an asphalt concrete pavement, depending on the location evaluated within the pavement structure as well as climate conditions.

A number of warm-mix asphalt (WMA) technologies are used to reduce the temperature at which the asphalt mixtures are produced and compacted, apparently without compromising the performance of the pavement. The main objective of this study is to determine whether the use of an innovative wax-based LEADCAP WMA additive influences the performance of the asphalt mixture, which is produced and compacted at significantly low temperatures. The WMA pavement using LEADCAP additive (WMA-LEADCAP) along with a control HMA pavement was evaluated with respect to their performances of rutting resistance, crack resistance, and viscoelastic property based on the laboratory dynamic modulus test, indirect tensile strength test, and in-door accelerated pavement test (APT) results. With the limited data carried out, the LEADCAP additive is effective in producing and paving asphalt mixture at approximately 30°C lower temperature than a control HMA mixture, and the performances of WMA-LEADCAP pavement are comparable to a control HMA pavement.

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