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The objectives of this study were to evaluate the effects of aggregate gradation and polymer modification on rutting and fatigue resistance of Superpave mixes. Asphalt mixes were prepared using three different gradations (above, through, and below the restricted zone) and three PG 70-22 binders (unmodified, SBS and SBR modified), and were evaluated using a triaxial repeated load test, a static creep, the Asphalt Pavement Analyzer, and the flexural beam fatigue test. When aggregates meeting Superpave angularity requirements was used, the effects of gradation on the rut and fatigue resistance of Superpave mixes were relatively small and the effects of the restricted zone was not significant. Even though binders used in this study had similar dynamic shear moduli, mixes containing polymer modified binders showed significantly lower resilient moduli than the unmodified mixes when measured in the indirect tensile and triaxial compressive modes. All laboratory test results indicated that the polymer modified mixes were significantly more rut resistant and fatigue resistant than the unmodified mixes with the same PG grading. Improvement in rut resistance due to polymer modification was shown to be most significant in the triaxial repeated load test, especially at a higher-temperature. Accelerated Pavement Load test results showed the similar trends regarding rutting performance. At higher test temperature or at a fast wheel speed, mixes with polymer modified binder performed better than mixes with an unmodified binder.
A major result of the research conducted under the Strategic Highway Research Program from 1987 to 1993 was the development of the Superpave (Superior Performing Asphalt Pavement) system for the comprehensive design of asphalt pavements. These 14 contributions describe the experience to date in the
Polymer modified asphalts have recently been the focus of much attention in the U.S. due to claims that polymer additives will lengthen the life of an asphalt pavement. Much of the published research on this topic has been concentrated on the effects of polymer modifiers on binder and mixture properties. The goal of this testing is to predict from laboratory testing the actual field performance of an asphalt concrete. Over the years, specifications have been developed for conventional asphalts that allow pavement performance to be predicted from certain binder tests. These conventional binder tests do not fully address the special characteristics of polymer modified asphalt binders and need revision to be an effective tool in predicting pavement service life. This paper presents the findings of a two-part laboratory research program intended to relate binder and mixture properties of polymer modified asphalts. The preliminary testing involved five asphalt binder types and a variety of binder and mixture tests. Promising test procedures were further investigated in the final testing program where ten asphalt binders were examined. Simple linear regression was used to determine the strength of a relationship between pairs of binder properties and mixture properties. The preliminary testing showed penetration, toughness and tenacity, and force ductility to have the most promise in predicting mixture performance. The final testing contained enough data to be analyzed with both simple linear regression and multiple regression. Penetration, toughness and tenacity, force ductility again were the test procedures that had binder properties that correlated well with mixture properties.
During the past 25 years, the U.S. National Academies of Sciences, Engineering, and Medicine, in collaboration with the Russian Academy of Sciences, have carried out a wide variety of activities to improve understanding of the challenges in containing and reducing ethnic conflicts, violent extremism, and terrorism. Roots and Trajectories of Violent Extremism and Terrorism provides an overview of this cross-ocean program, which has involved American and Russian scientists, engineers, and medical professionals from a large number of government agencies, leading research institutions, think tanks, educational institutions, analytical centers, and consulting and commercial firms in the two countries. This report highlights challenges addressed by the academies over many years that remain of current interest as the U.S., Russian, and other governments continue to cope with old and new forms of aggression that threaten the livelihood of populations at home and abroad.
Laboratory fatigue testing was performed on six Superpave HMA mixtures in use at the Virginia Smart Road. Evaluation of the applied strain and resulting fatigue life was performed to fit regressions to predict the fatigue performance of each mixture. Differences in fatigue performance due to field and laboratory production and compaction methods were investigated. Also, in-situ mixtures were compared to mixtures produced accurately from the job mix formula to determine if changes occurring between the laboratory and batch plant significantly affected fatigue life. Results from the fatigue evaluation allowed verification of several hypotheses related to mixture production and compaction and fatigue performance. It was determined that location within the pavement surface, such as inner or outer wheelpath or center-of-lane, did not significantly affect laboratory fatigue test results, although the location will have significant effects on in-situ fatigue life. Also the orientation of samples cut from an in-situ pavement (parallel or perpendicular to the direction of traffic) had only a minor effect on the laboratory fatigue life, because the variability inherent in the pavement due to material variability is greater than the variability induced by compaction. Fatigue life of laboratory-compacted samples was found to be greater than fatigue life of field-compacted samples; additionally, the variability of the laboratory compacted mixture was found to be less than that of the field-compacted samples. However, it was also found that batch-plant production significantly reduces specimen variability as compared to small-batch laboratory production when the same laboratory compaction is used on both specimen sets. Finally, for Smart Road mixtures produced according to the job mix formula, the use of polymer-modified binder or stone matrix asphalt was shown to increase the expected fatigue life. However, results for all mixes indicated that fatigue resistance rankings might change depending on the applied strain level. This study contributes to the understanding of the factors involved in fatigue performance of asphalt mixtures. Considering that approximately 95% of Virginia's interstate and primary roadways incorporate asphalt surface mixtures, and that fatigue is a leading cause of deterioration, gains in the understanding of fatigue processes and prevention have great potential payoff by improving both the mixture and pavement design practices.
The primary objective of this full-scale accelerated pavement testing was to evaluate the performance of unmodified and polymer modified asphalt binders and to recommend improved specification tests over existing SUperior PERforming Asphalt PAVEment (Superpave) binder performance grading methodologies. Candidate replacement tests were evaluated via their ability to discern fatigue cracking resistance and rutting. Two fatigue cracking specification tests were identified as more capable in capturing performance than others: binder yield energy and critical tip opening displacement. Two rutting specification tests that quantify irrecoverable deformations exhibited the best strength to capture rutting: multiple stress creep and recovery and oscillatory-based nonrecoverable stiffness. Based on the full-scale performance and laboratory tests, crumb rubber (recycled tires) modified asphalt (Arizona wet process) was shown to significantly slow or stop the growth of fatigue cracks in a composite asphalt pavement structure. A hybrid technique to modify asphalt with a combination of crumb rubber and conventional polymers (terminally blended) exhibited good fatigue cracking resistance relative to the control binder. Also, a simple addition of polyester fibers to asphalt mix was shown to have high resistance to fatigue cracking without the use of polymer modification. The research study also quantified the capabilities of the National Cooperative Highway Research Program's mechanistic-empirical pavement design and analysis methodologies to predict rutting and fatigue cracking of modified asphalts that were not captured in the calibration data from the Long-Term Pavement Performance program. Falling weight deflectometer, multidepth deflectometer, and strain gauge instrumentation were used to measure pavement response. The results illustrated that the nationally calibrated mechanistic-empirical performance models could differentiate between structural asphalt thickness but had difficulty differentiating modified from unmodified asphalt binder performance. Nonetheless, the mechanistic-empirical performance ranking and predictions were enhanced and improved using mixture-specific performance tests currently being implemented using the asphalt mixture performance tester.
New developments in asphalt with bio-oil, rubber and polymer componentsEmpirical data and models on binders, aggregates, RAP, WMA, HMA for pavementSpecial section on asphalt paving research in IndiaFully-searchable text on CD-ROM (included) The latest volume of the AAPT series features over two dozen research presentations devoted to the chemistry, engineering, modeling and testing of asphalt materials and processing. Developments in the use of components like bio-oil are discussed, as are strategies for testing asphalt components for wear and durability at low and high temperatures. The book offers new data on the performance of reclaimed/recycled materials in asphalt paving. A special section focuses exclusively on discussions of binder modifications. The CD-ROM displays figures and illustrations in articles in full color along with a title screen and main menu screen. Each user can link to all papers from the Table of Contents and Author Index and also link to papers and front matter by using the global bookmarks which allow navigation of the entire CD-ROM from every article. Search features on the CD-ROM can be by full text including all key words, article title, author name, and session title. The CD-ROM has Autorun feature for Windows 2000 with Service Pack 4 or higher products along with the program for Adobe Acrobat Reader with Search 11.0. One year of technical support is included with your purchase of this product.