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Hot mix asphalt (HMA) is a granular composite material stabilized by the presence of asphalt binder. The behavior of HMA is highly influenced by the microstructure distribution in terms of the different particle sizes present in the mix, the directional distribution of particles, the distribution of voids, and the nucleation and propagation of cracks. Conventional continuum modeling of HMA lacks the ability to explicitly account for the effect of microstructure distribution features. This study presents the development of elastic and visco-plastic models that account for important aspects of the microstructure distribution in modeling the macroscopic behavior of HMA. In the first part of this study, an approach is developed to introduce a length scale to the elasticity constitutive relationship in order to capture the influence of particle sizes on HMA response. The model is implemented in finite element (FE) analysis and used to analyze the microstructure response and predict the macroscopic properties of HMA. Each point in the microstructure is assigned effective local properties which are calculated using an analytical micromechanical model that captures the influence of percent of particles on the microscopic response of HMA. The moving window technique and autocorrelation function are used to determine the microstructure characteristic length scales that are used in strain gradient elasticity. A number of asphalt mixes with different aggregate types and size distributions are analyzed in this paper. In the second part of this study, an elasto-visco-plastic continuum model is developed to predict HMA response and performance. The model incorporates a Drucker-Prager yield surface that is modified to capture the influence of stress path direction on the material response. Parameters that reflect the directional distribution of aggregates and damage density in the microstructure are included in the model. The elasto-visco-plastic model is converted into a numerical formulation and is implemented in FE analysis using a user-defined material subroutine (UMAT). A fully implicit algorithm in time-step control is used to enhance the efficiency of the FE analysis. The FE model used in this study simulates experimental data and pavement section.
A State-of-the-Art Guide to the Mechanics of Asphalt Concrete Mechanics of Asphalt systematically covers both the fundamentals and most recent developments in applying rational mechanics, microstructure characterization methods, and numerical tools to understand the behavior of asphalt concrete (AC). The book describes the essential mathematics, mechanics, and numerical techniques required for comprehending advanced modeling and simulation of asphalt materials and asphalt pavements. Filled with detailed illustrations, this authoritative volume provides rational mechanisms to guide the development of best practices in mix design, construction methods, and performance evaluation of asphalt concrete. Mechanics of Asphalt covers: Fundamentals for mathematics and continuum mechanics Mechanical properties of constituents, including binder, aggregates, mastics, and mixtures Microstructure characterization Experimental methods to characterize the heterogeneous strain field Mixture theory and micromechanics applications Fundamentals of phenomenological models Multiscale modeling and moisture damage Models for asphalt concrete, including viscoplasticity, viscoplasticity with damage, disturbed state mechanics model, and fatigue failure criteria Finite element method, boundary element method, and discrete element method Digital specimen and digital test-integration of microstructure and simulation Simulation of asphalt compaction Characterization and modeling of anisotropic properties of asphalt concrete
The micro- and nano-modification of infrastructure materials and the associated multi-scale characterization and simulation has the potential to open up whole new uses and classes of materials, with wide-ranging implications for society. The use of multi-scale characterization and simulation brings the ability to target changes at the very small scale that predictably effect the bulk behavior of the material and thus allowing for the optimization of material behavior and performance. The International RILEM Symposium on Multi-Scale Modeling and Characterization of Infrastructure Materials (Stockholm, June 10-12, 2013) brought together key researchers from around the world to present their findings and ongoing research in this field in a focused environment with extended discussion times. From asphalt to concrete, from chemistry to mechanics, from nano- to macro-scale: the collection of topics covered by the Symposium represents the width and depth of the currently ongoing efforts of developing more sustainable infrastructure materials. Researchers, practitioners, undergraduates and graduate students engaged in infrastructure materials or multi-scale characterization and modeling efforts can use this book as a comprehensive reference, to learn about the currently ongoing research efforts in this field or as an inspiration for new research ideas to enhance the long-term performance of infrastructure materials from a fundamental perspective. The Symposium was held under the auspices of the RILEM Technical Committee on Nanotechnology-Based Bituminous Materials 231-NBM and the Transport Research Board (TRB) Technical Committee on Characteristics of Asphalt Materials AFK20.
This dissertation presents a novel micromechanics-based lattice procedure designed to characterize the cracking performance of hot mix asphalt (HMA) from its constituent material properties. The approach essentially consists of a series of direct-lattice models integrated with multiscale technique. A typical direct-lattice modeling starts with a preprocessor that discretizes the microstructure of a specimen, which is either physically or virtually fabricated, into a random truss lattice. The mixture performance can be predicted by analyzing such lattice network using a general-purpose finite element program FEP++. The cracking process in HMA is simulated by successive removal of failed links representing microcracks. In this study, a surface energy based failure criterion is developed to trigger the creation and subsequent extension of microcracks. Due to the disparate length scales associated with microcracking and specimen size, the direct-lattice modeling described above would demand unrealistic computational cost for modeling even a laboratory scale HMA specimens. In order to make the procedure more practical, the multiscale approach is implemented. Essentially, multi-scale model considers the effect of different-sized aggregates at different length scales. Such an approach reduces the computational cost significantly, while capturing the mechanical phenomenon at various length scales. Finally, the effectiveness of the proposed multiscale lattice procedure is illustrated by modeling an actual indirect tensile (IDT) test on a thin cylindrical HMA specimen and making quantitative comparisons with experimental measurements, including full-strain fields measured by the digital image correlations (DIC) technique.
Based on the Biot conference, named after Maurice Biot and held at Columbia University, this book contains over 170 original papers on different phases of poromechanics in many materials from soils and minerals to human bone. It covers testing and modeling.
Analysis of Pavement Structures brings together current research and existing knowledge on the analysis and design of pavements and introduces load and thermal stress analyses of asphalt and concrete pavement structures in a simple and step-by-step manner. For the second edition of this book, a new chapter on numerical implementation (using FEM) of pavement analysis is added along with topics such as mechanical modeling of granular materials, applications of convolution theorems in visco-elasticity, visco-elastic Poisson’s ratio, concepts of fracture mechanics in relation to fatigue of asphalt mix, solution of semi-infinite and so forth. New solved examples and schematic diagrams are also added. Features: Presents a simple, step-by-step approach for pavement analysis including systematic compilation of research work in the area Discusses further elaborations in terms of extended analytical formulations on some selected topics Includes new chapter on finite element analysis for pavement structures Contains more solved examples to understand the concepts better Explores primary application of pavement analysis in pavement thickness design This book is aimed at graduate students, structural mechanics researchers, and senior undergraduate students in civil/pavement/highway/transport engineering.
This book presents the latest advances in research to analyze mechanical damage and its detection in multilayer systems. The contents are linked to the Rilem TC241 - MCD scientific activities and the proceedings of the 8th RILEM International Conference on Mechanisms of Cracking and Debonding in Pavements (MCD2016). MCD2016 was hosted by Ifsttar and took place in Nantes, France, on June 7-9, 2016. In their lifetime, pavements undergo degradation due to different mechanisms of which cracking is among the most important ones. The damage and the fracture behavior of all its material layers as well as interfaces must be understood. In that field, the research activities aims to develop a deeper fundamental understanding of the mechanisms responsible for cracking and debonding in asphalt concrete and composite (e.g. asphalt overlays placed on PCC or thin cement concrete overlay placed on asphalt layer) pavement systems.
In the recent past, new materials, laboratory and in-situ testing methods and construction techniques have been introduced. In addition, modern computational techniques such as the finite element method enable the utilization of sophisticated constitutive models for realistic model-based predictions of the response of pavements. The 7th RILEM International Conference on Cracking of Pavements provided an international forum for the exchange of ideas, information and knowledge amongst experts involved in computational analysis, material production, experimental characterization, design and construction of pavements. All submitted contributions were subjected to an exhaustive refereed peer review procedure by the Scientific Committee, the Editors and a large group of international experts in the topic. On the basis of their recommendations, 129 contributions which best suited the goals and the objectives of the Conference were chosen for presentation and inclusion in the Proceedings. The strong message that emanates from the accepted contributions is that, by accounting for the idiosyncrasies of the response of pavement engineering materials, modern sophisticated constitutive models in combination with new experimental material characterization and construction techniques provide a powerful arsenal for understanding and designing against the mechanisms and the processes causing cracking and pavement response deterioration. As such they enable the adoption of truly "mechanistic" design methodologies. The papers represent the following topics: Laboratory evaluation of asphalt concrete cracking potential; Pavement cracking detection; Field investigation of pavement cracking; Pavement cracking modeling response, crack analysis and damage prediction; Performance of concrete pavements and white toppings; Fatigue cracking and damage characterization of asphalt concrete; Evaluation of the effectiveness of asphalt concrete modification; Crack growth parameters and mechanisms; Evaluation, quantification and modeling of asphalt healing properties; Reinforcement and interlayer systems for crack mitigation; Thermal and low temperature cracking of pavements; and Cracking propensity of WMA and recycled asphalts.