Understanding fracture resistance of asphalt concrete is of great importance in designing pavements with long service life. This thesis focused on studying the micro and global fracture behavior of heterogeneous asphalt concrete with a numerical analysis approach. Finite element (FE) models were built with the capacity of taking heterogeneity into consideration. The asphalt concrete was modeled as a multi-phase material with coarse aggregates and fine aggregate matrix (FAM). Viscoelastic properties were assigned to the FAM. Different damage models were incorporated to study fracture at two length scales: micro-fracture within FAM and coarse aggregate-FAM interface under small displacement and global fracture resistance in the semi-circular bending (SCB) test. For micro-fracture simulation, asphalt mixture was modeled with both adhesive and cohesive failure potential. Two different fracture models, cohesive zone model (CZM) and extended finite element model (XFEM), were adopted to simulate fracture damage within the FAM (cohesive failure) and at the FAM-aggregate interface (adhesive failure), respectively. For global fracture properties, the SCB test was simulated to predict the crack propagation pattern and the load-crack mouth opening displacement (CMOD) curve of asphalt concrete. Parametric studies with different material properties of FAM and coarse aggregates-FAM interface, morphological characteristics of coarse aggregates, and testing conditions (loading rate and temperature) were carried out to study their effects on fracture behavior of asphalt concrete. The numerical models provide an effective method to study fracture mechanism of heterogeneous asphalt concrete and generates meaningful findings. The development of cracking shows that the damage in the FAM material would initiate first at a small displacement and then interconnect with the damage developed at the FAM-aggregate interface. The higher angularity and larger aggregate size induces the greater damage level; while the orientation angle along with aspect ratio has influence on the anisotropic behavior of asphalt concrete. On the other hand, the SCB test simulations show good agreements with experimental results in the literature. Increasing fracture strength and energy of FAM significantly improves fracture resistance of asphalt concrete. The spatial distribution and angularity of coarse aggregate affect crack path; while the gradation and size of coarse aggregate affect fracture strength of asphalt concrete.

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

This book discusses the applications of fracture mechanics in the design and maintenance of asphalt concrete overlays. It provides useful information to help readers understand the effects of different material and loading type parameters on the fracture properties of asphalt concretes. It also reviews relevant numerical and experimental studies, and describes in detail design parameters such as aggregate type, air void, loading mode, and additives, based on the authors experience and that of other researchers.

For several decades, rutting in asphalt pavements has not been fully addressed or prevented. Study on the microstructure of asphalt concrete may provide a good alternative way to approach a solution. Conventional microstructure modeling based on computed tomography (CT), however, is expensive, time consuming, and specimen destructive. In this paper we present a study on discrete element modeling of asphalt concrete in which the microstructure is described based on the compositional phases. This approach is less expensive, more rapid, nondestructive, and easier to use relative to the CT approach. First, a new algorithm for generating coarse aggregate elements with irregular shapes is developed. It considers the shape and orientation distribution of particles in the microstructure of asphalt concrete. The irregular shapes are created based on the mechanism of sieving analysis. The random distribution of orientations is modeled with a rotation algorithm. Some particular problems such as the issue of "floaters" are solved with an iteration method in the proposed algorithm. Second, the air void phase, which is treated as the second microstructure component of asphalt concrete, is established with a regression model based on data measured from specimens fabricated with a Superpave gyratory compactor. Finally, the developed microstructural model of asphalt concrete is validated with volume fractions of phases in actual asphalt mixture specimens. The results are quite satisfactory.