The overall objective of this study was to determine if the Superpave high-temperature rheological properties of polymer-modified asphalt binders correlate to asphalt mixture rutting resistance. An emphasis was placed on evaluating polymer-modified asphalt binders with identical (or close) high-temperature performance grades (PG's), but varied polymer chemistries. Eleven asphalt binders were obtained for this study: two unmodified asphalt binders, an air-blown asphalt binder, and eight polymer-modified asphalt binders. High-temperature asphalt binder properties were measured by a dynamic shear rheometer (DSR). Mixture rutting resistance was measured by repeated shear at constant height (RSCH), and the French Pavement Rutting Tester (French PRT). The first objective was to verify the findings of a previous study using a different aggregate. In the previous study, it was found that the Superpave high-temperature asphalt binder properties correlated to mixture rutting resistance with few outliers, and a change in high-temperature PG from 70 to 76 increased rutting resistance. However, the correlation between RSCH and asphalt binder G*/sind (delta) depended on DSR frequency. The data suggested that a low DSR frequency, such as 0.1 rad/s, might provide a better grading system than the standard DSR frequency of 10.0 rad/s. This would require a change in the current asphalt binder specification. A diabase aggregate was used in a previous study. The data using a second aggregate, a limestone aggregate, in combination with four of the asphalt binders, agreed with the findings from the diabase mixtures. The second objective was to retest the diabase mixtures at 70 degrees Celsius using RSCH. The test temperatures used in the previous study were 50 degrees Celsius for RSCH and 70 degrees Celsius for the French PRT. The polymer-modified asphalt binders had continuous high-temperature PG's ranging from 71 to 77. Therefore, it was recommended that the test temperature for RSCH be increased to 70 degrees Celsius. Again, the correlation between RSCH and G*/sind was dependent on DSR frequency. The data suggested that a low DSR frequency, such as 0.1 rad/s, might provide a better grading system. However, it is not known whether this finding applies to pavements, or is related to the accelerated nature of the RSCH test. Furthermore, G*/sind (delta) at 0.1 rad/s did not clearly provide a better correlation to RSCH than the high-temperature PG's of the asphalt binders. The degree of correlation between the French PRT and G*/sind at 70 degrees Celsius did not depend on DSR frequency, and there was only one outlier. A correlation between the French PRT and high-temperature PG provided no obvious outliers. No changes to the specification are recommended based on the French PRT results.

In light of requirements that rubber be mixed with any asphalt used in projects receiving federal aid beginning in 1994, and the general increase in the problem of what to do with waste material, 17 papers from a December 1992 symposium in Miami discuss some of the technical and economic considerati

In their quest to improve overall pavement performance and durability, pavement engineers in recent years developed and used innovative asphalt mixtures utilising engineered or modified asphalt binders. The technology of asphalt modification using refining processes has evolved in the past decade as a viable, effective alternative. Results of an extensive evaluation of several paving asphalt binders modified by refining processes are presented and discussed. The evaluation used testing and characterisation systems developed in the Strategic Highway Research Program (SHRP) and recent revisions of these systems as proposed in the NCHRP 9-10 project. Rheological, failure and ageing properties at temperatures that simulate pavement service were measured and analysed. Handling, constructability and performance characteristics of asphalt binders modified by refining processes are evaluated and compared with those of conventional materials and asphalt modified by different types of polymers. Comparative performance results on asphalt mixtures are presented to show the effect of the improvements in binder characteristics on mixture performance. Results on new binder test methods developed as part of NCHRP 9-10 are also presented comparing binder and mixture performance characteristics. For the covering abstract of this conference see ITRD number E211271.

In recent years, a wide range of methods, such as incorporating Recycled Asphalt Pavement (RAP) and Ground Tire Rubber (GTR), have been used to reduce the cost of the asphalt mixtures and to produce an environmentally friendly asphalt pavement. A GTR-modified asphalt mixture can be produced through a wet or a dry process. In addition to the financial and environmental benefits of using GTR, its potential effect on performance characteristics of the pavement should also be considered. This thesis presents the evaluation of the performance characteristics of asphalt-rubber mixtures produced through wet process and a modified dry process. In the wet process, GTR is blended into the asphalt binder at an elevated temperature. The modified dry process refers to a method of adding the treated GTR directly to the HMA mixtures at a lower temperature. The modified dry process can facilitate the use of rubber in the asphalt industry by lowering the energy consumption and eliminating the expensive costs associated with shear mixing GTR and binder. In order to observe the performance characteristics of mixtures prepared through wet and modified dry processes, a 12.5 mm asphalt rubber gap-graded control mixture was developed through a wet process in accordance with ADOT material specification (Section 413). The same mixture was redesigned by incorporating two types of treated GTR through the modified dry process at a relatively lower temperature. The low temperature fracture properties were evaluated by Disk-Shaped Compact Tension Test (DCT). The rutting performance of asphalt mixtures was determined by Hamburg Wheel Tracking Device (HWTD). Mixtures produced by the wet process presented good low temperature fracture resistance. Mixtures produced by both wet and modified dry methods were able to conform to the Massachusetts specification against rutting distress. Finally, GTR and TGTR could improve the rutting and low-temperature fracture resistance of the asphalt mixtures.