Flavio V. Souza

MODEL FOR PREDICTING DAMAGE EVOLUTION IN HETEROGENEOUS VISCOELASTIC ASPHALTIC MIXTURES

Cracking in the asphaltic layer of pavements has been shown to be a major source of distress in roadways. Previous studies in asphaltic mixture cracking typically have not considered the material heterogeneity. The sequel of a study in which the binder and the aggregates were treated as distinct materials is presented. Besides consideration of the viscoelastic behavior of the bulk asphalt binder, a micromechanical viscoelastic cohesive zone model introducing ductility at the crack tip has been considered. The simulations performed are verified and calibrated from simple and conventional laboratory tests. The study investigates crack evolution under monotonic loading, even though the method outlined can be further developed for the investigation of asphalt mixture fatigue.

Experimental Testing and Finite-Element Modeling to Evaluate the Effects of Aggregate Angularity on Bituminous Mixture Performance

This study evaluates the effects of aggregate angularity in bituminous mixtures. Previous studies have predominantly focused on the effects of aggregate angularity on the resistance to permanent deformation, while little work has investigated the role of aggregate angularity related to mixture volumetrics and fatigue performance. To investigate the effect of aggregate angularity on mixture performance and characteristics, five mixes with different combinations of coarse and fine aggregate angularity are evaluated by performing the uniaxial static creep test and the indirect tensile fracture energy test. The asphalt pavement analyzer test is also performed with five-year field project mixtures. Fracture energy test results are then incorporated with finite element simulations of virtual specimens produced to explore the detailed mechanisms of cracking related to the aggregate angularity. Rutting performance test results indicate that higher angularity in the mixture improves rut resistance due to better aggregate interlocking. The overall effect of angularity on the mixturesi¯ resistance to fatigue damage is positive because aggregate blends with higher angularity require more binder to meet mix design criteria, which mitigates cracking due to increased viscoelastic energy dissipation from the binder, while angular particles produce a higher stress concentration that results in potential cracks. Finite element simulations of virtual specimens support findings from experimental tests.

Multiscale Modeling to Predict Mechanical Behavior of Asphalt Mixtures

This study presents a multiscale computational model for predicting the mechanical behavior of asphalt mixtures. The model can account for mixture heterogeneities by considering individual mixture constituents through the scale-linking technique: a local scale in a form of the heterogeneous representative volume element and a global scale that has been homogenized from local scale responses. The model is implemented with a finite element formulation, so that geometric complexities, material inelasticity, and the growth of time-dependent damage can be properly handled. Damage is in the form of cracks modeled with nonlinear viscoelastic cohesive zones. The primary purpose of this paper is to present the multiscale modeling framework developed and to evaluate the applicability of the multiscale modeling technique to determine the performance of asphalt mixtures and structures when damaged. This is accomplished by employing only material properties at the constituent level (local scale) as model inputs. The indirect tensile test of fine-aggregate matrix mixture is simulated as an example, and the simulation results are compared with experimental results to evaluate the applicability of the model. Predictive power of the model and the benefits related to the reduction of computational efforts and laboratory tests are further discussed.

Computation of Homogenized Constitutive Tensor of Elastic Solids Containing Evolving Cracks

The determination of the equivalent (homogenized) constitutive tensor is one of the most important steps in multiscale models as well as in the classical homogenization theory. In this article, a procedure for determining the homogenized instantaneous (tangent) constitutive tensor of elastic materials containing growing cracks is proposed. The primary purpose of this procedure is its use in two-way coupled multiscale finite element algorithms that can model crack formation and propagation at the local microstructure. The procedure is basically developed by relating the local displacement field to the global strain tensor at each location and using first-order homogenization techniques. The finite element formulation is developed and some example problems are presented in order to verify and demonstrate the model capabilities.

Multiscale model for asphalt mixtures subjected to cracking and viscoelastic deformation

The study reported in this paper presented a multiscale computational model, along with its validation and calibration, to predict the damage-dependent behavior of asphalt mixtures subjected to viscoelastic deformation and cracking. Asphalt mixture is a classic example of a multiphase composite that represents different lengths of scales. The understanding of the mechanical behavior of asphaltic materials has been a challenge to the pavement mechanics community because of the multiple complexities involved: heterogeneity, anisotropy, nonlinear inelasticity, and damage growth in multiple forms. To account for this issue in an accurate and efficient way, the study reported here presented a two-way linked multiscale computational modeling approach. The two-way linked multiscale model had its basis in continuum thermomechanics and was implemented with a finite element formulation. With the unique multiscale linking between scales and the use of the finite element technique, this model could take into account the effects of material heterogeneity, viscoelasticity, and anisotropic damage growth in small-scale mixtures on the overall performance of larger-scale structures. Along with the brief theoretical model formulation, the multiscale model was validated and calibrated through the comparison of the numerical, analytical, and experimental results of three-point bending beam tests of asphalt mixture samples that involved viscoelasticity, mixture heterogeneity, and cohesive zone fracture.

Verification of a Two-Way Coupled Multiscale Finite Element Code for Dynamic/Impact Problems

Engineering applications are increasingly facing structural challenges. Restrictive economic constraints and more complex geometric design have led to the use of advanced materials, such as fiber-reinforced composites. The behavior of such materials is governed by their microstructure, thus demanding the use of multiscale approaches. The present article aims at the verification of a two-way coupled multiscale finite element code previously developed by the authors. A two-scale analytical solution for a functionally graded elastic material subject to dynamic loads is herein derived in order to verify the multiscale code. Comparisons to overkilled single scale finite element solutions are also presented.

Multiscale Modeling of Bituminous Mixtures Considering Material Viscoelasticity and Cohesive Zone Fracture

This study presents a multiscale computational model and its potential applications to mechanical behavior predictions of bituminous materials, mixtures, and pavement structures. The multiscale model is based on continuum thermo-mechanics and is implemented using a finite element formulation. Two length scales (global and local) are two-way coupled in the model framework by linking a homogenized global scale to a heterogeneous local scale representative volume element (RVE). With the unique multiscaling and the use of the finite element technique, it is possible to take into account the effect of material heterogeneity, inelasticity, and damage accumulation in the small scale on the overall performance of larger scale mixtures or structures. This paper is not to provide any realistic predictions yet but to briefly introduce the model framework and demonstrate the potential applicability of the model in the field of bituminous materials and mixtures through an example simulation of asphalt concrete mixtures.