| Abstract: | Healing of microcracking in hot-mix asphaltic concrete pavements occurs to differing degrees. Adequate knowledge of the mechanisms of healing and how to enhance them, when applied in practice, would greatly increase service lives of roadways and result in major economic savings. This research sought to determine those characteristics and fundamental properties of asphalt cements that influence their ability to cause healing in hot-mix asphaltic concretes. In this effort, correlations among asphalt concrete mechanical healing and asphalt cement dispersion, settling, FT-IR chemical functional groups and NMR chemical structure were evaluated. Dependent or Y variable data to signify healing were obtained from the healing index, H, Heithaus dispersion and Laramie Energy Technology Center settling tests. Independent or X variable data described either asphalt cement characteristics or fundamental chemical composition and structure. Independent variable data was obtained by the Corbett analysis, XH or proton nuclear magnetic resonance and Fourier Transform-Infrared spectroscopy. In particular, the Corbett analysis allowed the division of the more complex asphalt cements into their more homologous generic fractions of saturates, napthene aromatics, polar aromatics and asphaltenes. The results of the experimental analysis and data reduction showed healing in hot-mix asphalt concretes to be directly proportional to the lengths and amounts of aliphatic molecules in the saturates and aliphatic side chains on napthene aromatics, polar aromatics and asphaltene materials. Both 1H NMR and FT-IR pointed to longer-chained saturates materials in some asphalt cements and not in others. The asphalt cements that healed better according to the healing index test procedure had significantly longer aliphatic materials than the asphalt cement that healed the least. The healing index test procedure was found to be the most direct indicator of healing. The L. E. T. C. settling test was found to be strongly correlated with healing index results, although not all asphalt cements are measurable by this test as indicated by Shamrock asphalt cement results. |
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