- Asphalt concrete fatigue cracking is recognized as a major distress mode in the U.S. The widespread nature of this distress and the data from agency Pavement Management Systems (PMS) suggest that it is an issue with asphalt mixture design and production processes and is not a problem specific to certain highway construction projects. The constituents of asphalt mixtures are continuously increasing such as increased recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS), rejuvenators, compaction aids, warm-mix additives, fibers, rubbers, etc. As a result, interactions between these constituents are complicating the mixture design process, relying solely on the volumetric mixture design is usually not resulting in asphalt mixtures with the highest possible performance. Thus, asphalt mixture test methods for rutting and cracking should be improved and incorporated into current mixture design methods. To achieve reliable cracking performance, cracking tests should be modified and improved to be able to develop more durable asphalt mixtures that last for their intended service lives. The major focus of this research study was to develop a new mixture design methodology for Oregon through four interrelated parts.
In Part I, the most effective test for characterizing Oregon asphalt mixtures was determined by evaluating four tests commonly used to evaluate fatigue cracking resistance. Results of tests were checked against actual field performance data to determine the most accurate test method for agencies and contractors. Testing time, cost, efficiency, complexity, and practicality were the other factors considered in the test method selection process. In Part II, using the cracking test [Semi Circular Bend (SCB)] selected in Part I, the impact of asphalt mixture variables, such as binder content, air-void content, aggregate gradation, and polymer modification, on cracking performance of Oregon asphalt mixtures were determined. The impact of those variables on rutting resistance was also determined by conducting flow number (FN) tests. In Part III, the most effective asphalt mixture long-term aging protocol was determined to achieve reliable SCB test parameters that are correlated with in-situ cracking performance. In Part IV, using the cracking test (SCB) selected in Part I and the aging protocol developed in Part III, a balanced asphalt mixture design method was developed.
It is expected that the fundamental findings of this research will facilitate the implementation of a new asphalt mixture design methodology for agencies and contractors which will, in turn, improve the longevity of asphalt materials, reduce life-cycle costs for agencies, and improve long-term road user comfort.
|Funding Statement (additional comments about funding)
- I would like to thank the Oregon Department of Transportation (ODOT) for sponsoring the research studies given in this dissertation. I would also like to extend my appreciation to ODOT Pavement Services Division, Justin Moderie, Larry Ilg, Michael Stennett, and Chris Duman, and ODOT research, Norris Shippen, for all their help and support throughout my study.