The characteristics of Crumb Rubber Modifier (CRM) modified asphalt and polymer Styrene-Butadiene-Styrene (SBS) modified asphalt were studied in this dissertation. Specifically, the objectives of this study include the following: (i) investigation of the rheological properties of CRM and SBS modified asphalt binders, (ii) development of optimum mix design for the CRM and SBS modified asphalt mixtures, and (iii) characterization of performance and durability properties of the CRM and SBS modified asphalt mixtures, such as rutting resistance, low-temperature thermal cracking resistance, and resistance to water induced damage.; The Marshall testing procedure, with minor modifications of selection criteria, was used to determine the optimum binder content for CRM and SBS modified mixtures. The selected mixtures were then characterized by various property or performance tests. To evaluate the rutting resistance performance of these modified mixtures, the incremental creep test, loaded wheel track test were conducted. Test results showed that the SBS modified mixtures, were more rutting resistant than the conventional unmodified mixture. To evaluate the low temperature thermal cracking resistance of the modified mixtures, TSRST test was performed. Test results showed that almost all the modified mixtures were more resistant to thermal cracking than the conventional mixtures. The durability of the modified mixtures was evaluated using the water sensitivity test. It was found that CRM modified mixtures tend to be more susceptible to water induced damage than the conventional mixture. The obvious phenomenon observed for this test was that CRM modified mixture specimens have excessive swelling in volume during water conditioning, which apparently resulted in their low tensile strength. The SBS modified mixtures, however, show little swelling and thus retain higher tensile strength after conditioning, even though they have a lower tensile strength ratio than the control mix.
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