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Keywords: asphalt mixtures, time-temperature superposition, viscoelastoplastic model.
The objective of this research is to develop an accurate and advanced material characterization model for predicting response of asphalt mixtures subjected to compression loading. The first step of the modeling is to check the validity of the time-temperature superposition principle for asphalt concrete with growing damage and viscoplastic strain in the compression state. Constant crosshead rate compression test results are used to construct the stress-log reduced time master curves for various strain levels. Research results indicate that asphalt concrete with growing damage remains thermorheologically simple (TRS), and that the time-temperature shift factor is only a function of temperature and is independent of the strain level. The model encompasses the elastic, plastic, viscoelastic, and viscoplastic strain components of asphalt concrete behavior and the effects of test conditions such as temperature and loading rate on the major strain components. The modeling approach is to model each response component separately and then integrate the submodels to obtain the final viscoelastoplastic model. The viscoelastic component, including elastic strain, is modeled based on Schapery's continuum damage theory and work potential theory, whereas Uzan's strain hardening model forms the basis of the viscoplastic model that also includes the plastic strain component. The testing program required for calibrating the viscoelastoplastic model is composed of small-strain complex modulus testing at various temperatures and frequencies to determine linear viscoelastic properties, constant crosshead rate testing at low temperatures/fast loading rates for viscoelastic modeling, and repeated creep and recovery testing at high temperatures for viscoplastic modeling. The developed viscoelastoplastic model performs well in predicting material responses up to peak stress.
The objective of the research presented is to develop an accurate and advanced material characterization procedure to be incorporated in the Superpave performance models system. The procedure includes the theoretical models and its supporting experimental testing protocols necessary for predicting responses of asphalt mixtures subjected to tension loading. The model encompasses the elastic, viscoelastic, plastic and viscoplastic components of asphalt concrete behavior. Addressed are the major factors affecting asphalt concrete response such as: rate of loading, temperature, stress state in addition to damage and healing. Modeling strategy is based on modeling strain components separately and then adding the resulting models to attain a final integrated ViscoElastoPlastic model. Viscoelastic response, including elastic component, is modeled based on Schapery's continuum damage theory comprising of an elastic-viscoelastic correspondence principle and work potential theory. As for the viscoplastic response, which includes the plastic component, its characterization stems from Uzan's strain hardening model. The testing program required for developing the models consists of complex modulus testing for determination of material response functions, constant crosshead rate testing at low temperatures for viscoelastic modeling, and repetitive creep and recovery testing for viscoplastic modeling. The developed model is successful in predicting responses up to localization when microcracks start to coalesce. After that, fracture process zone strains detected using Digital Image Correlation are used to extend the model's ability in predicting responses in the post-localization stage. However, once major macrocracks develop, the currently developed model ceases to accurately predict responses. At that state, the theory of fracture mechanics needs to be integrated with the current continuum damage-based model.
Keywords: asphalt concrete characterization, ViscoElastoPlastic, viscoelasticity, viscoplasticity, viscoelastic response functions, machine compliance, time temperature superposition, air voids measurement, specimen geometry.
Premature cracking in asphalt pavements and overlays continues to shorten pavement lifecycles and creates significant economic and environmental burden. In response, RILEM Technical Committee TC 241-MCD on Mechanisms of Cracking and Debonding in Asphalt and Composite Pavements has conducted a State-of-the-Art Review (STAR), as detailed in this comprehensive book. Cutting-edge research performed by RILEM members and their international partners is presented, along with summaries of open research questions and recommendations for future research. This book is organized according to the theme areas of TC 241-MCD - i.e., fracture in the asphalt bulk material, interface debonding behaviour, and advanced measurement systems. This STAR is expected to serve as a long term reference for researchers and practitioners, as it contributes to a deeper fundamental understanding of the mechanisms behind cracking and debonding in asphalt concrete and composite pavement systems.
Performance characteristics of bituminous mixtures play the most influential role in designing flexible pavement. These asphaltic mixtures can be considered as heterogeneous mixtures which composed of two primary components: fine aggregate matrix (FAM) phase and aggregate phase. The FAM phase acts as a critical phase in evaluating the performance characteristics including viscoelastic, fatigue damage, and permanent deformation characteristics of entire asphalt mixtures. This study evaluates the viscoelastic, fatigue damage and permanent deformation characteristics of bituminous mixtures containing 65% reclaimed asphalt pavement (RAP) by performing oscillatory torsional shear tests of cylindrical bars of FAM using a dynamic mechanical analyzer. Moreover, this study investigates a linkage between performance characteristics of asphalt concrete (AC) mixture and its corresponding FAM phase. To meet the objectives of this study, laboratory tests were performed for several FAM mixtures with 65% reclaimed asphalt pavement and different types of rejuvenators and one warm mix asphalt (WMA) additive. Test results were then analyzed using viscoelastic theories and fatigue prediction models based on continuum damage mechanics. Furthermore, obtained laboratory test results were compared with corresponding test results of asphalt concrete mixtures. The test results indicated that rejuvenators change properties and performance behavior related to fatigue damage and permanent deformation of high reclaimed asphalt pavement mixtures. In addition, test results of FAM phase were generally linked well with asphalt concrete mixture test results, and they vividly depicted that FAM phase could provide core information to predict the behavior of the asphalt concrete mixture.