Francisco Thiago Sacramento Aragão

Micromechanical Model for Heterogeneous Asphalt Concrete Mixtures Subjected to Fracture Failure

Cracking is a main source of structural distress in asphalt materials and asphaltic pavements. To predict crack-associated fracture damage in asphalt mixtures, this study presents a model using the finite-element method and a cohesive zone fracture model. The approach allows advanced characterization of the microstructural damage evolution in a more realistic length scale, the mixture heterogeneity, the inelastic material behavior, and the interactions among mixture constituents. The model presented herein accounts for (1) actual mixture heterogeneity by using digital image techniques; (2) inelastic material behavior based on elastic-viscoelastic constitutive relations; and (3) microscale fracture damage represented by the cohesive zone fracture model. A computational modeling framework is presented, and the applicability of the model is demonstrated through simulations. Model simulations are further analyzed by comparing numerical predictions to laboratory test results and by conducting parametric analyses of fracture properties. It is expected that the successfully developed computational model can provide better insights into the effect of mixture constituents on overall mixture performance, while minimizing modeling efforts and producing more accurate simulations than traditional approaches, with significant savings in experimental costs and time.

Damage modeling of bituminous mixtures considering mixture microstructure, viscoelasticity, and cohesive zone fracture

This paper describes the development and application of a computational modeling approach incorporated with pertinent laboratory testing that can be used to predict fracture damage performance of bituminous paving mixtures. In the model, material viscoelasticity, mixture microstructure, and cohesive zone fracture properties are implemented within a finite element method, which is intended to simulate nonlinear-inelastic microscale fracture and its propagation to complete failure in bituminous mixtures. The model is applied to different materials, and the resulting model simulations are compared to experimental results for model validation. With some limitations and technical issues to be overcome in the future, the model presented herein clearly demonstrates several advancements based on its features accounting for material viscoelasticity, heterogeneity, and cohesive zone fracture. Potentially, the model can provide significant savings in time and costs and can also be used to improve currently available...

Semiempirical, Analytical, and Computational Predictions of Dynamic Modulus of Asphalt Concrete Mixtures

Dynamic modulus is the key property used to characterize stiffness of asphaltic mixtures in pavement performance evaluation programs such as the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures. This paper investigates various models for predicting the dynamic modulus of asphalt mixtures and compares model predictions with experimental test results. The predictions of two semi-empirical models (Witczaks model, modified Hirsch model), an analytical micromechanics model (Hashins model), and the computational micromechanics model are compared with the dynamic modulus test results obtained from cylindrical asphalt concrete specimens. For the computational micromechanics approach, the finite element method was incorporated with laboratory tests that characterize the properties of individual mixture constituents and with a digital image analysis technique to represent detailed microstructure characteristics of asphalt concrete mixtures. All predicting models investigated in this paper are in fair agreement with the test results. Witczaks equation simulates dynamic moduli somewhat greater than laboratory test results, whereas the modified Hirsch model generally underpredicts moduli. The computational micromechanics model presents a relatively higher deviation at lower loading frequencies, but it shows better predictions because the loading frequency is higher. Hashins analytical micromechanics model is limited to accurately predicting the dynamic modulus of the asphalt mixtures because of geometric simplifications and assumptions. With further improvements, the computational micromechanics method incorporated with the testing protocol seems attractive, because it can directly account for geometric complexity due to aggregates and inelastic mixture component properties with fewer of the required laboratory tests.

Modeling Fracture and Failure of Heterogeneous and Inelastic Asphaltic Materials Using the Cohesive Zone Concept and the Finite Element Method

This study presents a computational micromechanics approach based on the finite element method (FEM) to model heterogeneous, inelastic asphalt mixtures with rate-dependent fracture failure. The model accounts for the mixture heterogeneity as FEM meshes are generated from the digital images of actual specimens. The inelastic nature of the mixtures is modeled by including the viscoelastic constitutive relation of the material and the fracture process zone, which is modeled by the cohesive zone concept. A computational modeling framework and related experimental protocols are presented, and the applicability of the model is demonstrated through virtual testing simulations of asphalt concrete mixtures. Model simulations are discussed by comparing predictions to the laboratory test results. It is expected that the model with further improvements can provide better insights into the effects of mixture constituents on the overall mixtures performance, while reducing modeling efforts and achieving significant savings in experimental costs and time.