Taesun You

Continuum Coupled Moisture–Mechanical Damage Model for Asphalt Concrete

Despite the detrimental effects of moisture damage in asphalt pavements, few macroscale models are capable of modeling this important phenomenon. Existing models have limitations in accounting for the irreversibility and time dependency of moisture-induced damage. This study presents a moisture damage model based on continuum damage mechanics. Adhesive and cohesive moisture damage phenomena are modeled independently; this procedure allows for the introduction of fundamental mechanical properties for each process and for modeling the transition between adhesive and cohesive damage. Two- and three-dimensional simulations are performed, and the results of the simulations are presented to demonstrate the applicability and utility of these micromechanical computational models. It is shown that the proposed moisture damage model can simulate the effect of moisture damage on the mechanical response of asphalt concrete subjected to different loading conditions. The model also provides useful insight into the effect of mixture design and material properties on resistance to moisture damage.

Multiscale testing-analysis of asphaltic materials considering viscoelastic and viscoplastic deformation

Abstract Fine aggregate matrix (FAM) is a phase consisting of asphalt binder, air voids, fine aggregates and fillers. It acts as a primary phase in evaluating the damage and deformation of entire asphalt concrete mixtures. The simplicity, repeatability and efficiency of the FAM testing make it a very attractive specification-type approach for evaluating the performance characteristics of the entire asphalt concrete mixtures. This study explores a linkage in the deformation characteristics between the two length scales: asphalt concrete mixture scale and its corresponding FAM scale. To that end, a simple creep-recovery test was conducted for both mixtures (i.e. asphalt concrete mixture and its corresponding FAM phase) at various stress levels. Test results were compared and analysed using Schapery’s single-integral viscoelastic theory and Perzyna-type viscoplasticity with a generalised Drucker–Prager yield surface. In particular, stress-dependent nonlinear viscoelastic and viscoplastic behaviours were characterised in addition to linear viscoelastic deformation characteristics, because the nonlinear viscoelastic and viscoplastic behaviours are considered significant in asphalt pavements that are subjected to heavy vehicle loads and elevated service temperatures. With a limited scope and test-analysis results at this stage, it was found that there is a strong link between the FAM and asphalt concrete in (linear and nonlinear) viscoelastic and viscoplastic deformation characteristics. This implies that the viscoelastic stiffness characteristics and viscoplastic hardening of typical asphalt concrete mixtures could be estimated or predicted from the simple FAM-based testing-analysis method, which can significantly reduce the experimental–analytical efforts required for asphalt concrete mixtures.

Three-dimensional microstructural modelling of coupled moisture–mechanical response of asphalt concrete

Three-dimensional (3D) microstructural representation of asphalt concrete subjected to moisture diffusion and mechanical loading is simulated and analysed. The continuum moisture–mechanical damage mechanics framework and the moisture damage constitutive relationship developed by the authors are used in this study to couple the detrimental effects of the mechanical loading and moisture diffusion on the complex response of asphalt concrete. A 3D finite element (FE) microstructural representation of a typical asphalt concrete is used for these simulations. The 3D microstructure is reconstructed from slices of two-dimensional X-ray computed tomography images that consist of the matrix and the aggregates. Results show that the generated 3D FE microstructure along with the coupled moisture–mechanical constitutive relationship can be effectively used to simulate the overall thermo-hygro-mechanical response of asphalt concrete. The analyses provide insight into the impact of the microstructure on the overall response of asphalt concrete.

Three-Dimensional Microstructural Modeling of Asphalt Concrete by Use of X-Ray Computed Tomography

This paper presents a framework that combines experimental techniques and computational methods for modeling the microscopic response of asphalt mixtures subjected to various loading conditions. The basis of this framework is capturing the three-dimensional microstructure of asphalt mixtures with X-ray computed tomography and a sequence of image-processing methods to identify the microstructure components or mixture phases. This microstructure is then converted to a finite element model in which the various phases are represented with constitutive models that describe their mechanical behavior. In this study, the coarse aggregate phase was modeled as a linear elastic material, and the matrix phase (asphalt, fine particles, and air voids) was represented as a thermoviscoelastic, viscoplastic, and damage model. The analysis results showed that the model captured the effects of temperature, rate of loading, repeated loads, and mixture design on the microstructure response. These results demonstrate that the developed framework will help engineers and researchers to understand the effects of mixture design and material properties on performance and to establish the link between microscopic response and macroscopic behavior.

Three-Dimensional Microstructural Modeling Framework for Dense-Graded Asphalt Concrete Using a Coupled Viscoelastic, Viscoplastic, and Viscodamage Model

This paper presents a three-dimensional (3D) image-based microstructural computational modeling framework to predict the thermoviscoelastic, thermoviscoplastic, and thermoviscodamage response of asphalt concrete. X-ray computed tomography is used to scan dense-graded asphalt concrete (DGA) to obtain slices and planar images, from which the 3D microstructure is reconstructed. Image process- ing techniques are used to enhance the quality of images in terms of phase identification and separation of particles. This microstructure is divided into two phases: aggregate and matrix. The aggregate phase is modeled as an elastic material and the matrix phase is modeled as a thermoviscoelastic, thermoviscoplastic, and thermodamage material. Stress-strain response, damage propagation, and the distributions of the viscoelastic and viscoplastic strains are predicted by performing virtual uniaxial and repeated creep-recovery tests of the developed 3D model of asphalt concrete. The effects of loading rate, temperature, and loading type on the thermomechanical response of asphalt concrete are investigated. In addition, the microscopic and macroscopic responses of DGA are compared with those of stone matrix asphalt (SMA). The results demonstrate that SMA can sustain higher strain levels at the microscopic level and higher macroscopic ultimate strength. The damage in SMA is more localized than in DGA. The microstructure-based framework presented in this paper can be used to offer insight on the influence of the distribution and properties of microscopic constituents on the macroscopic behavior of asphalt concrete. DOI: 10.1061/ (ASCE)MT.1943-5533.0000860.

Calibration and Validation of a Comprehensive Constitutive Model for Asphalt Mixtures

A nonlinear thermoviscoelastic, thermoviscoplastic, and thermo-visco damage constitutive model was developed recently to predict the response of asphalt mixtures under loading. This paper presents a systematic approach to determine the parameters of the model. The paper also demonstrates the efficacy of this approach through the calibration and validation of the model through various tests conducted on fine aggregate mixtures (FAM) and full asphalt mixtures. The dynamic modulus test was conducted to obtain linear viscoelastic model parameters while repeated creep-recovery tests were performed to obtain nonlinear visco elastic and viscoplastic parameters. Viscodamage model parameters were obtained through the constant strain rate test. Once the model was calibrated, it was validated through a comparison of the predicted results with measurements from repeated creep-recovery tests conducted at various combinations of recovery times and temperatures. The predicted responses for FAM and full asphalt mixtures on the basis of the model were found to be in good agreement with the experimental data. Model parameters obtained on the basis of laboratory testing provided useful insights into the relationship between FAM and full asphalt mixture responses and the material properties that affect these responses.

Experimental-Statistical Investigation of Testing Variables of a Semicircular Bending (SCB) Fracture Test Repeatability for Bituminous Mixtures

Given the fact that fracture is a primary distress causing pavement failure, it is important to identify and characterize the fracture/cracking properties of asphalt concrete mixtures and to include them in pavement design processes. This study examined the testing variables for a reliable and practical semicircular bending (SCB) fracture test to evaluate the fracture characteristics of asphalt concrete mixtures at intermediate service temperatures. An integrated experimental-statistical approach was employed to identify testing variables by which repeatable SCB test results can be achieved. Using a typical Nebraska asphalt mixture, five critical testing variables (i.e., the number of testing specimens, specimen thickness, notch length, loading rate, and testing temperature) of the SCB test were investigated due to their significant effects on mixture fracture characteristics. Statistical analysis of test results indicated that approximately six specimens/replicates were a reasonable sample size that could properly represent asphalt concrete fracture behavior of a typical dense-graded mixture. Then, the coefficient of variation (COV) of the mixture fracture energy for six specimens was used to evaluate the effects of other remaining test variables. A range of a specimen thickness of 40 to 60 mm, a notch length from 5 to 40 mm, and a testing temperature between 15 and 40°C showed the reasonably low COV value of fracture energy at around or less than 10 %. The loading rates (0.1 to 10 mm/min.) attempted in this study did not show any significant differences in the testing repeatability.

Mechanistic Modeling to Evaluate Structural Performance of Bituminous Pavements with Inelastic Deformation and Fatigue Damage of Mixtures

AbstractThis study modeled structural performance of bituminous pavements with inelastic deformation and fatigue damage. Two major distresses, namely rutting and fatigue damage, of typical bituminous pavements were modeled by extending the pavement analysis using nonlinear damage approach (PANDA), a recently-developed finite-element approach to model damage-associated pavement performance, by incorporating main features in the PANDA with a fracture mechanics approach so as to improve the capability in predicting rate-dependent localized behavior of bituminous mixtures in pavement structures. More specifically, the Schapery’s nonlinear viscoelasticity and Perzyna-type viscoplasticity featured in the PANDA were used to characterize recoverable and irrecoverable deformation of bituminous paving mixtures, and damage of bituminous mixtures due to multiple microscale and macroscale cracks was characterized using the cohesive zone fracture law, which was incorporated with a relevant fracture test such as a semic...

Use of Semicircular Bending Test and Cohesive Zone Modeling to Evaluate Fracture Resistance of Stabilized Soils

The fracture resistance of a chemically stabilized base or subbase layer is important to the durability and sustainability of a pavement structure. Thus, an appropriate test protocol to characterize the fracture resistance of stabilized bases, subbases, and subgrade soils is essential to the design of pavement materials and structures. This paper proposes a protocol developed on the basis of the semicircular bending test to measure fracture resistance (i.e., fracture energy and fracture toughness) of chemically stabilized material. The effects of three test variables, including specimen thickness, notch length, and loading rate, on fracture properties were investigated, and appropriate values for these test variables were selected for the semicircular bending test protocol. The proposed semicircular bending test method was successful in characterizing the fracture resistance of three chemically stabilized materials. To address fracture properties of the chemically stabilized material more definitively, three-dimensional zone modeling was used and the simulations agreed very well with the experimental results. Both the fracture properties obtained from the experiment and the cohesive zone modeling indicated that polymer-stabilized limestone exhibited a much higher fracture resistance than cement-stabilized limestone and cement-stabilized sand. However, the polymer used demonstrated susceptibility to degradation in the presence of water. Correction of this limitation is the focus of ongoing research on this type of polymer.