Characterization of Healing of Asphalt Mixtures Using Creep and Step-Loading Recovery Test
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by ASTM Int'l (all rights reserved). Healing of asphalt mixtures has been proven to be significant, and different approaches exist to characterize it, such as the phenomenological methods, mechanism-based, and mechanicsbased methods. To target the actual causal relationship for healing in asphalt mixtures, a new test called the creep and step-loading recovery (CSR) test, along with a new mechanistic method termed the energy-based mechanistic (EBM) approach, was previously developed by the authors. This paper aimed at examining the applicability of the CSR test with the EBM approach in characterizing healing of asphalt mixtures. A variety of asphalt mixtures were selected and subjected to the CSR test in this study. The internal stress measured by the CSR test was used in the EBM approach to generate a damage density progression curve, which directly reflected how the damage developed and healed in the tested material. Based on this curve, the normalized extent of healing was defined as a direct measure of healing, and the healing curve (the normalized extent of healing versus the rest time) was defined as a straightforward tool to qualitatively evaluate the healing ability of asphalt mixtures. To further achieve a quantitative description of the healing ability, a healing model based on the Ramberg-Osgood equation was developed to simulate the healing curve. The parameters in the healing model represent the healing speed at different stages of healing (the initial healing rate and ultimate healing rate) and the overall ability of the material to heal (the healing scale). Both the healing curves and healing parameters can discern the difference in the healing ability caused by the air void content, aging, temperature, and the type of asphalt binder. In other words, the CSR test, along with the EBM approach, was able to produce a reasonable and consistent prediction of healing for asphalt mixtures.
Journal of Testing and Evaluation
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Luo, Xue||Lytton, Robert L