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10 Use reasonably priced equipment that can be shared between the requirements of the ideal aging procedure for specification the short- and long-term procedures. testing were used to select approaches and candidate procedures for further consideration. This step eliminated microwave technology. 2.2.2 Review and Selection Process The third step in the evaluation and selection process con- A three-step process was used to select promising proce- sisted of a detailed comparison of candidate procedures based dures for further evaluation in NCHRP Project 9-36. The first on the two viable approaches with the requirements of the step included two activities that were conducted simultane- ideal aging procedure. This step also included the considera- ously at the beginning of the project. These were the devel- tion of a hybrid procedure combining meritorious elements opment of the requirements of the ideal aging procedure for of the various procedures reviewed. From this step, two exist- specification testing as discussed previously in Section 2.2.1, ing procedures, the MGRF and the SAFT, were identified as and a review of literature and research in progress associated promising methods for further consideration. with binder aging methods. Excellent literature reviews on the aging of asphalt binders and mixtures were conducted during the SHRP asphalt research program (35). These formed the 2.3 Selection Study basis for the expanded literature review performed during this The objective of the selection study was to evaluate whether study. Approximately 90 references that post-date the SHRP the two promising short-term aging tests, the MGRF and the asphalt research were identified and reviewed. Much of this SAFT, can be extended to long-term aging. The extension of information was published in the European literature, espe- either of these to a low-temperature, long-term aging test using cially that of Eurobitume and RILEM. Several ongoing stud- air at atmospheric pressure depends on the mixing efficiency ies associated with the development of improved binder aging of the device. The selection study evaluated the mixing effi- methods were identified, and contact was made with the prin- ciency of the devices at conditions representative of those that cipals conducting these studies. The work in progress that was should be used in a long-term aging test. In this study, the level reviewed included of aging obtained for long-term conditions was compared to that obtained in the PAV. Table 2-1 presents the conditions Efforts at the Western Research Institute under FHWA Con- selected by the research team for developing prototype versions tract DTFH61-99-C-00022, "Fundamentals of Asphalts and of long-term aging tests based on the MGRF and the SAFT. Modified Asphalts II," associated with the chemistry of The selection study was conducted in two parts. The first binder aging; part of the study was an assessment of various modifications FHWA studies to evaluate the Modified Rolling Thin Film that could be made easily to the MGRF and the SAFT to pro- Oven Test, MGRF, and SAFT; duce prototype long-term versions of these tests. The goal in Texas Department of Transportation studies associated this effort was to obtain approximately the same degree of with the development and implementation of the SAFT; aging that occurs in the PAV subject to the constraints on tem- Activities in the European Committee for Standardiza- perature, atmosphere, and time given in Table 2-1. The binders tion (CEN) Task Group on Binder Aging (CEN TC336 SG1 used in this part of the study were a neat PG 58-28, a styrene- TG3); and Shell Global Solutions' research associated with the devel- butadiene-styrene (SBS) modified PG 82-22, and a low-density opment of the Long-Term Rotating Flask Test. polyethylene (LDPE) modified PG 76-22. Table 2-2 presents the test conditions that were varied during this first part of Appendix A (available on the TRB website) presents a the selection study. The suitability of each of the various comprehensive bibliography related to binder aging that was configurations was assessed based on assembled by adding the references identified in this project to the unpublished literature review prepared during the SHRP The degree of aging obtained relative to the PAV for the PG asphalt research (3). Relevant findings from the literature 58-28 and the PG 82-22, review and the review of research in progress are presented in Chapter 3 of this report. The second step in the evaluation and selection process Table 2-1. Summary of conditions for was the selection of candidate procedures from those identi- long-term aging used in the selection study. fied through the literature review and the review of research Condition Value in progress. Procedures based on (1) microwave technology, Temperature 100C max (2) thin films, and (3) air blowing were identified in the review Atmosphere Air at atmospheric pressure Duration < 48 hours of the literature and research in progress. Consideration of Quantity Per current short-term testing protocol the fundamental aging process in these three approaches and Degree of Aging Approximate PAV aging