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| Author | : Zhanping You |
| Publisher | : |
| Total Pages | : 1024 |
| Release | : 2003 |
| Genre | : |
| ISBN | : |
| Author | : |
| Publisher | : |
| Total Pages | : |
| Release | : 2021 |
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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.
| Author | : Dallas N. Little |
| Publisher | : Springer |
| Total Pages | : 702 |
| Release | : 2017-09-25 |
| Genre | : Technology & Engineering |
| ISBN | : 331958443X |
This textbook lays out the state of the art for modeling of asphalt concrete as the major structural component of flexible pavements. The text adopts a pedagogy in which a scientific approach, based on materials science and continuum mechanics, predicts the performance of any configuration of flexible roadways subjected to cyclic loadings. The authors incorporate state-of the-art computational mechanics to predict the evolution of material properties, stresses and strains, and roadway deterioration. Designed specifically for both students and practitioners, the book presents fundamentally complex concepts in a clear and concise way that aids the roadway design community to assimilate the tools for designing sustainable roadways using both traditional and innovative technologies.
| Author | : Minkyum Kim |
| Publisher | : |
| Total Pages | : 268 |
| Release | : 2011-09-09 |
| Genre | : |
| ISBN | : 9781243752802 |
The viscoelastic modulus of hot-mix asphalt (HMA) such as the complex modulus, E*, is an essential material parameter for better paving mixture design and asphalt pavement design. Under certain circumstances, it is desirable that a reasonable modulus value of certain HMA mixtures be estimated for this purpose. Empirical and semi empirical models have been proposed and used. However, these non-fundamental approaches have significant drawbacks, particularly with application of the model for materials that vary from those used in the calibration of the model, and their reliance on large calibration data sets, which led to introducing some fuzzy factors in their predictions. In order to overcome the limitations of an empirical approach, a fundamental micromechanics modeling framework based on the differential scheme effective medium theory has been developed and introduced herein. To verify and validate the prediction accuracy and applicability, a series of various asphalt-aggregate mixtures starting from the homogeneous asphalt binder phase up to a very highly packed composite of dense HMA mixtures were produced in the lab by progressively increasing the aggregate volume concentration in the composite from 0 to nearly 0.9. These various mixtures were tested in the Hollow Cylinder Tensile Tester (HCT) to obtain the extensional complex modulus (E*) at three low temperatures within -25 to 5C range and at various loading frequencies from 10 Hz to 0.01 Hz. Comparisons between the model predicted E* and the experimental E* showed good agreement with reasonable accuracies. Remaining challenges for the practical implementation of the proposed model such as the applicability at intermediate to high temperature materials property prediction and particle orientation effects were discussed based on the analysis and additional model predictions for an independent experimental data set.
| Author | : Ala R. Abbas |
| Publisher | : |
| Total Pages | : 324 |
| Release | : 2004 |
| Genre | : Asphalt |
| ISBN | : |
| Author | : Samer Hassan Dessouky |
| Publisher | : |
| Total Pages | : 146 |
| Release | : 2005 |
| Genre | : Aggregates (Building materials) |
| ISBN | : |
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 aggregate particles present in the mix, the directional distribution of aggregates, 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 aggregate microstructure distribution features. This report presents the development of elastic and visco-plastic models that account for important aspects of the aggregate and microstructure distribution in modeling the macroscopic behavior of HMA. The objective of Project 0-1707 is to develop tools by which engineers can judge the impact of the aggregate on the performance of HMA based on simple and repeatable tests. Of greatest concern in Project 0-1707 is the ability of the HMA to resist permanent deformation or to rut, which leads to safety concerns, especially under wet surface conditions. In this report, the research team develops an approach is developed to introduce a length scale to the elasticity constitutive relationship in order to capture the influence of aggregate particle sizes on HMA response. A finite element (FE) analysis is used to analyze the microstructure response and predict the macroscopic properties of HMA. Each point in the microstructure is assigned effective local properties that are calculated using an analytical micromechanical model that captures the influence of the number of particles on the microscopic response of the 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 . 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 project simulates experimental data and pavement section.
| Author | : Jingsong Chen |
| Publisher | : |
| Total Pages | : 178 |
| Release | : 2011 |
| Genre | : |
| ISBN | : |
Asphalt mixture compaction is an important procedure of asphalt mixture construction and can significantly affect the performance of asphalt pavement. Many laboratory compaction methods (or devices), have been developed to study the asphalt mixture compaction. Nevertheless, the whole process from the selection of aggregate to laboratory compaction is still time-consuming and requires significant human and material resources. In order to better understand asphalt mixture compaction, some researchers began to use finite element method (FEM) to study and analyze mixture compaction. However, FEM is a continuum approach and lacks the ability to take into account the slippage and interlocking of aggregates during compaction. Discrete Element Method (DEM) is a discontinuum analysis method, which can simulate the deformation process of joint systems or discrete particle assembly under quasi-static and dynamic condition. Therefore, it can overcome the shortcomings of FEM and is a more effective tool than FEM to simulate asphalt mixture compaction. In this study, an open source 3D DEM code implemented with the C++ programming language was modified and applied to simulate the compaction of hot-mix asphalt (HMA). A viscoelastic contact model was developed in the DEM code and was verified through comparison with well established analytical solutions. The input parameters of the newly developed contact model were obtained through nonlinear regression analysis of dynamic modulus test results. Two commonly used compaction methods (Superpave gyratory compaction and asphalt vibratory compaction) and one linear kneading compaction based on APA machine were simulated using the DEM code, and the DEM compaction models were verified through the comparison between the DEM predicted results and the laboratory measured test results. The air voids distribution within the asphalt specimens was also analyzed by post processing virtual DEM compaction digital specimens and the level of heterogeneity of the air void distribution within the specimens in the vertical and lateral directions was studied. The DEM simulation results in this study were in a relatively good agreement with the experimental data and previous research results, which demonstrates that the DEM is a feasible method to simulate asphalt mixture compaction under different loading conditions and, with further research, it could be a potentially helpful tool for asphalt mix design by reducing the number of physical compactions in the laboratory.
| Author | : Enad Muhib Ahmad Mahmoud |
| Publisher | : |
| Total Pages | : |
| Release | : 2010 |
| Genre | : |
| ISBN | : |
Aggregate strength, gradation, and shape play a vital role in controlling asphalt mixture performance. Many studies have demonstrated the effects of these factors on asphalt mixture performance in terms of resistance to fatigue cracking and rutting. This study introduces numerical and analytical approaches supported with imaging techniques for studying the interrelated effects of aggregate strength, gradation, and shape on resistance of asphalt mixtures to fracture. The numerical approach relies on the discrete element method (DEM). The main advantage of this approach is the ability to account for the interaction between the internal structure distribution and aggregate properties in the analysis of asphalt mixture response and performance. The analytical approach combines aggregate strength variability and internal force distribution in an asphalt mixture to predict the probability of aggregate fracture. The numerical and analytical approaches were calibrated and verified using laboratory tests on various aggregate types and mixtures. Consequently these approaches were used to: (1) determine the resistance of various mixture types with different aggregate properties to fracture, (2) study the effects of aggregate strength variability on fracture, (3) quantify the influence of blending different types of aggregate on mixture strength, (4) develop a mathematical expression for calculating the probability of aggregate fracture within asphalt mixture, and (5) relate cracking patterns (cohesive: aggregate - aggregate and matrix - matrix, and adhesive: aggregate - matrix) in an asphalt mixture to internal structure distribution and aggregate properties. The results of this dissertation established numerical and analytical techniques that are useful for developing a virtual testing environment of asphalt mixtures. Such a virtual testing environment would be capable of relating the microscopic response of asphalt mixtures to the properties of the mixture constituents and internal structure distribution. The virtual testing environment would be an inexpensive mean to evaluate the influence of changing different material and design factors on the mixture response.
| Author | : Eyad Masad |
| Publisher | : CRC Press |
| Total Pages | : 879 |
| Release | : 2018-07-16 |
| Genre | : Technology & Engineering |
| ISBN | : 0429855796 |
Advances in Materials and Pavement Performance Prediction contains the papers presented at the International Conference on Advances in Materials and Pavement Performance Prediction (AM3P, Doha, Qatar, 16- 18 April 2018). There has been an increasing emphasis internationally in the design and construction of sustainable pavement systems. Advances in Materials and Pavement Prediction reflects this development highlighting various approaches to predict pavement performance. The contributions discuss links and interactions between material characterization methods, empirical predictions, mechanistic modeling, and statistically-sound calibration and validation methods. There is also emphasis on comparisons between modeling results and observed performance. The topics of the book include (but are not limited to): • Experimental laboratory material characterization • Field measurements and in situ material characterization • Constitutive modeling and simulation • Innovative pavement materials and interface systems • Non-destructive measurement techniques • Surface characterization, tire-surface interaction, pavement noise • Pavement rehabilitation • Case studies Advances in Materials and Pavement Performance Prediction will be of interest to academics and engineers involved in pavement engineering.
| Author | : Erol Tutumluer |
| Publisher | : CRC Press |
| Total Pages | : 1560 |
| Release | : 2009-06-15 |
| Genre | : Technology & Engineering |
| ISBN | : 0203865286 |
Bearing Capacity of Roads, Railways and Airfields focuses on issues pertaining to the bearing capacity of highway and airfield pavements and railroad track structures and provided a forum to promote efficient design, construction and maintenance of the transportation infrastructure. The collection of papers from the Eighth International Conference
