Over the past decade, the Texas Department of Transportation (TxDOT) focused research efforts on improving mixture design to preclude rutting in the early life of the pavement, which also offered increased resistance to moisture damage, but fatigue cracking may surface in the long term particularly if the binder stiffens excessively due to aging. The primary goal of this project is to evaluate and recommend a fatigue analysis system for TxDOT designs to ensure adequate mixture fatigue performance in a particular pavement structure under specific environmental and loading conditions. A secondary goal of comparing fatigue resistance of commonly used TxDOT mixtures including investigating the effects of aging will also be realized.

Over the past decade, the Texas Department of Transportation (TxDOT) focused research efforts on improving mixture design to preclude rutting in the early life of the pavement. However, these rut resistant stiff mixtures may be susceptible to long-term fatigue cracking in the pavement structure as the binder stiffens due to oxidative aging. To address this concern, TxDOT initiated a research study with the primary goal of evaluating and recommending a hot mix asphalt concrete (HMAC) mixture fatigue design and analysis system to ensure adequate mixture fatigue performance in a particular pavement structure under specific environmental and traffic loading conditions. A secondary goal of the research was to compare the fatigue resistance of commonly used TxDOT HMAC mixtures including investigating the effects of binder aging on fatigue performance.

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The recent changes in the Texas Department of Transportation (TxDOT) hot mix asphalt (HMA) mix design procedures to ensure that the mixture types routinely used on Texas highways are not prone to rutting raised concerns that these mixture types are now more susceptible to fatigue cracking. The primary goal of this study was to evaluate fatigue cracking test methods and recommend that which is both simple and robust, especially in qualifying commonly used Texas mixture types. One way to minimize fatigue cracking is through material screening and selection of appropriate mix designs that are representative of fatigue-resistant HMA mixes. However, there are not many standardized laboratory fracture resistance tests that have been universally adopted for routine mix design and/or screening purposes for HMA fatigue resistance. In this study, four different fracture test methods: the Overlay Tester (OT), Direct Tension (DT), Indirect Tension (IDT), and Semicircular Bending (SCB) tests were comparatively evaluated for their potential application as surrogate tests for routine fracture resistance evaluation and screening of HMA mixes in the laboratory. The evaluation criteria included: rationality of the test concept and correlation to field performance, repeatability and variability, simplicity and practicality of the sample fabrication process, and simplicity of data analysis. Results and key findings based on the laboratory fatigue resistance characterization of various commonly used Texas coarse- and fine-graded HMA mixes (Type B, C, and D) are presented in this paper. Overall, preliminary findings indicated that no monotonically-loaded test would be appropriate as a surrogate fatigue resistance test; however, the SCB test showed potential as a repeated-loading test. Suggested SCB test improvements include developing the repeated SCB test protocol, determining the appropriate failure criterion, and correlating laboratory performance to field performance.

The work contained in this report constitutes Phase II of Texas Department of Transportation (TxDOT) Project 0-4468. The primary objective of Phase II was to provide additional laboratory validation and sensitivity analysis of the calibrated mechanistic with (CMSE) and without (CM) surface energy measurements fatigue analysis approaches recommended in Report 0-4468-2. The second objective was to provide a better understanding of the binder-mixture relationships and effects of binder oxidative aging on both mixture fracture properties and fatigue life (N sub f). The third objective was to explore the possibility of establishing a surrogate fatigue test protocol based on the CMSE approach. These objectives were achieved through fatigue characterization of additional hot-mix asphalt concrete (HMAC) mixtures with different mix-design parameters and materials under varying laboratory aging exposure conditions.

At head of title: National Cooperative Highway Research Program.