National Academies Press: OpenBook

Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction (2017)

Chapter: CHAPTER 4 Suggested Future Research

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Page 121
Suggested Citation:"CHAPTER 4 Suggested Future Research." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. Washington, DC: The National Academies Press. doi: 10.17226/24959.
Page 121

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114 CHAPTER 4 Suggested Future Research Suggested future research is presented in Figure 2. In order to arrive at a final aging protocol, the interim aging protocol should be applied to RAP mixtures, WMA mixtures, and polymer-modified mixtures. The AIPs of the binders extracted and recovered from the laboratory-aged loose mixtures would be compared to those of the binders extracted and recovered from corresponding field cores. In addition, the compaction of loose mixtures after long-term aging for the various WMA technologies should be investigated. A diffusion model that considers the morphological properties of asphalt mixtures (e.g., binder film thickness, air voids) should be developed and coupled with the developed kinetics model to arrive at a pavement aging model. Such a model would improve the prediction of changes in asphalt binder properties with oxidative aging within pavement performance prediction frameworks, including Pavement ME Design. The diffusion model could be developed largely by evaluating the WesTrack mixtures, which include systematic changes in asphalt mixture morphology. The combined kinetics-diffusion model would then be calibrated against field core AIP measurements at varying depths using materials and field cores from various pavements in different climatic conditions, including Group B materials and pavements used in this study. The predicted changes in the binder properties with oxidative aging must be related to the changes in the asphalt mixture properties to facilitate the integration of the pavement aging model in pavement performance prediction frameworks. Therefore, a systematic study of laboratory-aged loose mixtures should be conducted whereby loose mixtures are prepared at three levels of long-term aging and subjected to dynamic modulus and cyclic fatigue performance testing. Asphalt binders would be extracted and recovered from the long-term aged loose mixtures and evaluated. The changes in the asphalt binder properties with oxidative aging would be related to the corresponding changes in the asphalt mixture dynamic modulus values and cyclic fatigue performance. Note that the current kinetics model allows only for the prediction of G* at 64°C and 10 rad/s. Thus, linking changes in binder properties with oxidative aging to corresponding changes in mixture performance may require establishing a means to predict the effects of aging over the range of temperatures and loading rates actually experienced by pavements. The performance test results of the systematic aging study will be integrated into FlexPAVE™ to predict pavement performance, with consideration given to the changes in mixture properties as a function of depth and time due to aging. The results will be analyzed to evaluate the effect of aging on cracking performance and to identify the depth within the pavement that is most critical to pavement performance. There is also the possibility to extend the kinetics-diffusion modeling framework to address the impact of oxidative aging in Accelerated Pavement Tests (APTs). The kinetics- diffusion modeling framework would be used to derive a tool for the prediction of the required APT conditions (i.e., time and temperature) to represent a given level of aging. In addition, a means to determine the appropriate laboratory aging conditions to produce performance test specimens with the same level of aging as a given APT and that has the capability to consider the effects of environmental exposure both prior to and/or after the APT and of thermal treatment during the APT should be developed.

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TRB’s National Cooperative Highway Research Program has released a pre-publication, non-edited Report 871: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. The report presents a proposed standard method for long-term laboratory aging of asphalt mixtures for performance testing. The method is intended for consideration as a replacement for the method in AASHTO R 30, “Mixture Conditioning of Hot Mix Asphalt (HMA),” which was the most commonly used method for aging asphalt materials for performance testing for input to prediction models for the past 25 years. The method improves on R 30 in that the laboratory aging time is specifically determined by the climate at the project location.

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