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Existing asphalt mixture design approaches are mainly empirical based "trial-and-error" methods. Based purely on volumetrics, such design methods have little consideration of the mechanical performance of the mixtures. With the trend of moving the pavement research into more mechanistic based methods and targeting the ultimate goal to good field performance, it is necessary to develop a sophisticated mix design and characterization methodology which can help the designer understand the expected engineering performance of the mix at the early stages, at the same time, to have a more efficient tool to evaluate the quality of the mixtures. This research develops a comprehensive aggregate gradation and asphalt mixture design method that estimates the mechanical properties of the mix at early stage. In this method, strong correlations between aggregate properties, volumetrics, and mechanical properties are identified, making the VMA (Voids in Mineral Aggregate) an excellent media to link the properties of aggregates and asphalt binder to their engineering performance. The concept of the design procedure, especially the aggregate gradation design procedure, is largely based on an analysis of aggregate packing and interlocking. As a fast and convenient design method that emphasizes more on the mechanical performance of the mix, the new design method can be used to evaluate the quality of an existing gradation and mix design, and adjust the gradation of a new mix to satisfy both volumetrics and mechanical properties. In addition, the characteristics of asphalt mixture are studied using micromechanical based discrete element method (DEM) and macromechanical modeling. In DEM simulation, an image based ball clumping technique is used for simulating the angularity properties of aggregate particles. The DEM model is established and calibrated to describe the viscoelastic (dynamic modulus and phase angle) and viscoelastic plastic (strength) properties of asphalt mixtures with or without damage involved. As for macromechanical modeling, a constitutive model for characterizing the permanent deformation of asphalt mixture is explored by taking consideration of the directional distribution of aggregates (anisotropy), and the damage induced by plasticity.
This paper reports the results of a research effort initiated in the early 1990s to develop a C-? (cohesion-angle of friction) characterization model for the design of asphalt mixtures and asphalt pavements. It is demonstrated that, since the model is based on the fundamental material properties represented by C and ?, it can derive analytically other asphalt mix design parameters such as Marshall stability and flow, and indirect tensile strength. The C-? characterization model therefore offers a useful basis for the development of a comprehensive design framework that integrates asphalt mix design with asphalt pavement structural design. To demonstrate this capability, the research developed an empirical-mechanistic rutting prediction model of asphalt pavement layer using the C-? characterization model. In addition, the model allows stresses and strains under design loading to be computed, which can be applied as input to structural analysis for asphalt material selection and pavement thickness design.
Pavement Design And Paving Material Selection are important for efficient, cost effective, durable, and safe transportation infrastructure Paving Materials and Pavement Analysis contains 73 papers examining bound and unbound material characterization, modeling, and performance of highway and airfield pavements. The papers in this publication were presented during the GeoShanghal 2010 International Conference held in Shanghai, China, June 3-5, 2010.
Abstract : Asphalt mixture is the most widely used pavement engineering material. Because the laboratory tests of asphalt mixture are costly, researchers keep searching for a practical numerical simulation approach to facilitate their study on mixture design, compaction process, and service performance. Although the discrete element method (DEM) had been introduced into those research areas for more than three decades and has been proved to be an effective tool, its utilizing is still limited by lacking coarse aggregate morphologies, efficient modeling approaches, and complete mechanical theories. This study aims to extend the application of DEM in asphalt mixture research by 1) establishing a coarse aggregate morphology database. Coarse aggregates were categorized according to shape information and then scanned through a three-dimensional scanner. The essential morphology factors, including grain size, dimensions, surface area, volume, and specific surface area, were collected and analyzed; 2) building the gyratory compaction process. Loose material assembly was precisely generated through the developed algorithm according to the mixture design. The loose material was then compacted through the programed gyration moment. The impacts of contact parameters on compaction were investigated. Speed-up techniques were proposed and verified by analyzing the internal structure of the compacted mixtures; 3) developing a set of modeling procedures with high efficiency, low cost, reliable accuracy, and wide application. The new modeling procedures use coarse aggregate temples from the database to improve simulation accuracy and use geometry information from the gyratory compacted mixtures or random generation method to save laboratory specimens. Hexagonal close-packed (HCP) structure, which has advantages in simulating shear failure and Poisson's ratio, was employed instead of the simple cubic-centered (SCC) structure. The corresponding mechanical calculation for contact micro-parameters was then derived and verify through simple stiffness/bond tests and complete indirect tensile (IDT) tests; 4) applying DEM models to research practice. Based on those improvements, this study involved DEM in the research of the mechanical performance of asphalt mixtures with high contents of ground tire rubber (GTR). Incorporate with laboratory tests, although asphalt mixtures with high contents of GTR have lower IDT strength of was than a conventional mixture, its cracking resistance and fatigue resistance were proved to be higher. By analyzing the contact force distribution in the DEM models, rubber particles with low moduli were found to be the endogenous reason for better performance. By further investigation, the rubber particles functioned as buffers that disperse the loadings. With the above four parts of research, the application of the DEM in asphalt mixture has significant improvement in modeling techniques, mechanical theories, simulation efficiency, and scope of application.
Both conventional asphalt mix design and current pavement structure design method, known as macro research techniques, cannot take all micro-meso-parameters into consideration. The relationship between meso-structural information and macroscopic mechanical responses was established by using locally effective material method. First, elastic properties of asphalt mortar were obtained based on the resilient modulus test, and an appropriate moving window size was used to calculate the coarse aggregate volume fraction, which was treated as a locally homogenous distribution. Additionally, accounting for the generation of homogenous materials, a locally effective material method was implemented by a mechanical approach method for different asphalt mixtures, and then effective models for finite-element method (FEM) were established. Finally, effective models were calibrated within a small displacement domain based on the digital image correlation monitoring test, and then the FEM results illustrated the different mechanical responses, which show a more reasonable distribution than original models. In conclusion, although effective FEM model are locally equivalent materials, this approach is an effective method without lacking of the ability to figure out these meso-structural differences among various asphalt mixtures.
Bituminous Mixtures and Pavements contains 113 accepted papers from the 6th International ConferenceBituminous Mixtures and Pavements (6th ICONFBMP, Thessaloniki, Greece, 10-12 June 2015). The 6th ICONFBMP is organized every four years by the Highway Engineering Laboratory of the Aristotle University of Thessaloniki, Greece, in conjunction with
In 1979, I edited Volume 18 in this series: Solution Methods for Integral Equations: Theory and Applications. Since that time, there has been an explosive growth in all aspects of the numerical solution of integral equations. By my estimate over 2000 papers on this subject have been published in the last decade, and more than 60 books on theory and applications have appeared. In particular, as can be seen in many of the chapters in this book, integral equation techniques are playing an increas ingly important role in the solution of many scientific and engineering problems. For instance, the boundary element method discussed by Atkinson in Chapter 1 is becoming an equal partner with finite element and finite difference techniques for solving many types of partial differential equations. Obviously, in one volume it would be impossible to present a complete picture of what has taken place in this area during the past ten years. Consequently, we have chosen a number of subjects in which significant advances have been made that we feel have not been covered in depth in other books. For instance, ten years ago the theory of the numerical solution of Cauchy singular equations was in its infancy. Today, as shown by Golberg and Elliott in Chapters 5 and 6, the theory of polynomial approximations is essentially complete, although many details of practical implementation remain to be worked out.
In the years since the development and subsequent success of Stone Matrix Asphalt (SMA), a plethora of articles have emerged, scattered throughout various publications. The time is right for a comprehensive resource that collects, examines, and organizes this information and makes it easily accessible. A compilation and distillation of the latest k
At first glance, roads seem like the simplest possible geotechnical structures. However, analysis of these structures runs up against complexities related to the intense stresses experienced by road surfaces, their intense interaction with climate, and the complicated behavior of the materials used in road construction. Modern mechanistic approaches to road design provide the tools capable of developing new technical solutions. However, use of these approaches requires deep understanding of the behavior of constituent materials and their interaction with water and heat which has recently been acquired thanks to advances in geotechnical engineering. The author comprehensively describes and explains these advances and their use in road engineering in the two-volume set Geotechnics of Roads, compiling information that had hitherto only been available in numerous research papers. Geotechnics of Roads: Advanced Analysis and Modeling develops 23 extended examples that cover most of the theoretical aspects presented in the book Geotechnics of Roads: Fundamentals. Moreover, for most examples, Volume 2 describes algorithms for solving complex problems and provides Matlab® scripts for their solution. Consequently, Volume 2 is a natural complement of the book Geotechnics of Roads: Fundamentals. This unique book will be of value to civil, structural and geotechnical engineers worldwide.