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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 973: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results refines the aging procedure developed in the original NCHRP Research Report 871: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. The updates field calibrate the original project aging model (PAM), develop procedures to estimate the PAM inputs, and develop a framework by which the predicted changes in asphalt binder properties that are due to oxidative aging can be related to corresponding changes in asphalt mixture performance.
A study was conducted to determine the effects of long term oven aging of asphalt mixtures (AASHTO PP2-95) on the thermal cracking performance evaluation of mixtures using the SUPERPAVE Indirect Tensile Test (IDT). Asphalt mixtures were aged according to the procedures developed by the Strategic Highway Research Program (SHRP) and tested using the SUPERPAVE Indirect Tensile Test after short- and long-term oven aging. The results were used to make thermal cracking performance predictions using the Penn State Thermal Cracking Model, which is a part of the SUPERPAVE mixture analysis system. The analyses indicated that: 1) long-term oven aging of mixtures produced changes in mixture compliance that led to differences in thermal cracking performance predictions, 2) long-term oven aging can produce excessive aging which results in erroneous (unconservative) performance predictions and 3) the relative ranking of thermal cracking performance of short-term oven-aged mixtures is, for most cases, the same as that of long-term oven aged mixtures. In other words, the system distinguished between mixtures with significantly different performance levels regardless of whether the mixtures were tested after short-term oven aging or long-term oven aging. This finding implies that long-term oven aging may not be justified for mixture specification purposes when the SUPERPAVE low temperature performance evaluations are used.
This is a report on the state of the art of research on the phenomenon of the aging of asphalt-aggregate mixtures. Compared to research on the aging of asphalt cement, there has been little research on the aging of asphalt mixtures. Binder studies are considered as well as mixture sutdies, the relationship between laboratory aging tests and field performance, and the relationship between chemical composition and field performance. Recommendations are made for aging procedures which show promise for laboratory investigation. Test methods to evaluate aging are also considered. It is noted that extended heating procedures show the most promise for short-term aging and pressure oxidation and/or extended heating the most promise for long-term aging.
Aging phenomenon of asphalt material exists in the course of mixing, spreading, and rolling of asphalt mixture, as well as the use in the asphalt pavement. The indirect tensile strength test was used to evaluate the performance of asphalt mixtures at low-temperature under different aging conditions. As compared with the results from the original short-term aging and the long-term aging asphalt mixtures, the results show that the original asphalt mixture cannot reflect the real performance of the asphalt mixture in the field. The short-term aging specimens are more sensitive than long-term aging specimens in evaluating the performance of the asphalt mixture at low temperature. Tests results also indicate that the consideration of aging during the evaluation of asphalt pavement performance is necessary.
The hardening or stiffening associated with heating asphalt is referred to as aging and occurs in two stages: short-term aging, which occurs during mixture mixing and placement, and long-term aging, which occurs throughout the life of the pavement. A portion of the Strategic Highway Research Program has been dedicated to developing accelerated performance tests for aging asphalt mixtures. Two test procedures developed at the Oregon State University utilize oven aging at 135 deg C and 85 or 100 deg C to simulate short- and long-term field aging. This report presents the results of the field validation of these two procedures.
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
Bituminous Mixtures and Pavements VIII contains 114 papers as presented at the 8th International Conference ‘Bituminous Mixtures and Pavements’ (8th ICONFBMP, 12-14 June 2024, Thessaloniki, Greece). The contributions reflect the research and practical experience of academics and practicing engineers from thirty-four (34) different countries, and cover a wide range of topics: Session I: Bitumen, Modified binders, Aggregates, and Subgrade Session II: Bituminous mixtures (Design, Construction, Testing, Performance) Session III: Pavements (Design, Construction, Maintenance, Sustainability, Energy and Environmental consideration) Session IV: Pavement management and Geosynthetics Session V: Pavement recycling Session VI: Pavement surface characteristics, Pavement performance monitoring, Safety Session VII: Biomaterials in pavement engineering Session VIII: Prediction models of pavement performance Bituminous Mixtures and Pavements VIII covers recent advances in highway materials technology and pavement engineering, and will be of interest to scientists and professionals involved or interested in these areas. The ICONFBMP-conferences have been organized every four years since 1992. This 8th conference was jointly organized by: Laboratory of Highway Engineering, Aristotle University of Thessaloniki, Greece; Built Environment Research Institute (BERI), University of Ulster, UK; University of Texas San Antonio (UTSA), USA; Laboratory for Advanced Construction Technology (LACT), Technological Institute of Iowa, USA; Technological University of Delft (TUDelft), The Netherlands, and University of Antwerp, (UA), Belgium.
Ideally, asphalt pavements are designed to achieve sufficient stiffness prior to the application of traffic to resist rutting while also maintaining enough flexibility after years of service to minimize the amount of durability/brittleness related distresses (e.g. cracking and weathering). Multiple factors have caused an industry transition to mixes which are much more susceptible to crack, and durability related distresses are often the primary mechanism by which pavements fail. To restore a balance between rutting and durability distresses in asphalt pavements, the industry has started investigating balanced mix designs (BMDs) While mitigating only rutting or cracking behaviors is a straightforward exercise based on the collection of knowledge, simultaneously considering the two types of distresses is challenging considering that rutting is an early life distress and durability distresses are not typically observed until longer term aging has occurred. Mixture conditioning protocols to simulate field aging in conjunction with tests to fairly evaluate mixture integrity after conditioning are needed to scrutinize asphalt mixtures for durability related distresses during the mixture design phase. The current longer term conditioning protocol (R30) adopted by the American Association of State Highway and Transportation Officials (AASHTO) is not as severe as suggested when considering durability/brittleness (Isola et al. 2014; Yin et al. 2016; Cox et al. 2017). This dissertation’s primary objective is to provide guidance on asphalt mixture aging by contributing in four areas: 1) ensuring proper density measurement of field aged cores, 2) provide guidance on increased short term aging time effects in asphalt mixtures, 3) suggest improved mixture conditioning protocols to simulate longer term field aging, and 4) make suggestions for improving binder conditioning protocols to simulate longer term field aging. To these ends, a series of mixture and extracted binder tests were conducted on materials that were used to construct a full-scale test section in Columbus, MS that was monitored for aging for up to 5 after construction. The overall work presented provides simple recommendations or protocols which have the potential to improve the level of scrutiny that can be given to paving materials during the mix design phase and thus improve overall pavement performance.
This report provides a brief summary of the processes that led to the selection of performance-related tests to define asphalt-aggregate interactions that result in fatigue, permanent deformation, thermal cracking, aging, and water sensitivity. Inherent in this test selection process was the emphasis on the ability of the tests to measure fundamental material properties that, when incorporated into prediction models, will depend less on empirical correlations than has been traditionally the case. Also included are the results of validation studies for each of the tests and frameworks for the use of the tests in mix design and analysis. Several levels of design are provided for each distress, some of which incorporate reliability concepts.