Micromechanical Analysis of Viscoelastic Properties of Asphalt Concretes (original) (raw)
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Journal of Materials in Civil Engineering, 2014
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 processing 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.
International Journal of Advances in Engineering Sciences and Applied Mathematics, 2011
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Construction and Building Materials, 2012
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.
Micromechanical finite element framework for predicting viscoelastic properties of asphalt mixtures
Materials and Structures, 2008
A micromechanical finite element (FE) framework was developed to predict the viscoelastic properties (complex modulus and creep stiffness) of the asphalt mixtures. The two-dimensional (2D) microstructure of an asphalt mixture was obtained from the scanned image. In the mixture microstructure, irregular aggregates and sand mastic were divided into different subdomains. The FE mesh was generated within each aggregate and mastic subdomain. The aggregate and mastic elements share nodes on the aggregate boundaries for deformation connectivity. Then the viscoelastic mastic with specified properties was incorporated with elastic aggregates to predict the viscoelastic properties of asphalt mixtures. The viscoelastic sand mastic and elastic aggregate properties were inputted into micromechanical FE models. The FE simulation was conducted on a computational sample to predict complex (dynamic) modulus and creep stiffness. The complex modulus predictions have good correlations with laboratory uniaxial compression test under a range of loading frequencies. The creep stiffness prediction over a period of reduced time yields favorable comparison with specimen test data. These comparison results indicate that this micromechanical model is capable of predicting the viscoelastic mixture behavior based on ingredient properties.
Modeling the Impact of Testing Mode on the Viscoelastic Behavior of Asphalt Concrete
2023
The variations in the viscoelastic characteristics of asphalt concrete due to testing mode are assessed and modeled in the present investigation. Asphalt concrete mixture was prepared at its optimum asphalt binder requirement and compacted in slab mold with the aid of roller compaction. Beam specimens of 6.2 cm width, 5.6 cm depth, and 40 cm length, were obtained from the slab samples with the aid of a diamond saw, and tested using controlled stress and strain techniques under dynamic flexural stresses. The viscoelastic properties such as the phase angle, cumulative dissipated energy, permanent deformation, flexural stiffness, and micro strain were monitored and modeled among the two testing techniques. It was noticed that higher micro strain and permanent deformation are detected when testing the asphalt concrete specimens under constant strain mode. However, higher phase angle, flexural stiffness, and energy dissipation could be observed under the constant stress mode of the test.
International Journal of Pavement Engineering, 2015
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.
Micromechanical modeling of I-FIT asphalt concrete specimens
Asphalt concrete Semi-circular beam Illinois flexibility index Micromechanical modeling Fracture Finite elements Digital image correlation A B S T R A C T Analytical and numerical micromechanical models have been previously used to understand fracture behavior of heterogeneous materials like Portland cement concrete or asphalt concrete (AC). In this study, the behavior of asphalt concrete was studied during a semi-circular bending (SCB) fracture test, Illinois Flexibility Index Test (I-FIT), using micromechanical level finite element models. The models were validated in multiple steps using the strain fields calculated with the digital image correlation (DIC) technique as well as the global scale forces measured in the same experiment. The micromechanical model was developed to evaluate the effects of microstructural features such as aggregate gradation, aggregate distribution, and void space on fracture behavior of AC. The model focused on pre-peak behavior and assumed that AC consists of aggregates and mortar. Aggregates were considered linear elastic with material constants reported in the literature, while the mortar was assumed linear viscoelastic. Mortar was defined as the combination of binder, air voids, and material passing 2.36 mm sieve. Mixture theory was utilized to characterize the mortar as viscoelastic using binder's dynamic shear rheometer results, elastic properties of fine aggregate material, and air voids volume from the AC mix design. The validated FEM was used to perform a parametric study aimed at determining the effect of aggregate gradation and binder properties on the applied load, opening strains and stresses, and energy around the crack tip. Nine aggregate gradations and three binders were studied; ten replicates for each aggregate gradation-binder combination were considered. In order to create the replicates, a Python script that fabricates artificial aggregate gradations and randomly distributes aggregates in the I-FIT geometry was created. It was found that mortar properties, rather than air voids, binder content, or fine material, were heavily correlated to energy and applied load of the I-FIT specimen.
Modeling Linear Viscoelastic Properties of Asphalt Binders
Doboku Gakkai Ronbunshu, 1996
The linear viscoelastic properties of asphalt binders are analyzed based upon two different methods: (1) nomograph and (2) dynamic mechanical analysis. The former one is an empirical procedure which has been used by paving technologists for a long time while the latter one is used to directly measure the dynamic response of materials. The application of viscoelasticity to asphalt cements is explained in terms of master curves. It is shown that data obtained from nomographs are inaccurate and misleading compared to measured data. Several models are further presented to predict the linear viscoelastic properties of asphalt binder and found that one of these models can be adequately used for asphalt binders.
Influence of constant strain levels on the viscoelastic properties of asphalt concrete
2023
The flexural stresses applied by vehicular movement exhibit a great influence on the viscoelastic properties of asphalt concrete pavement. However, the fatigue life of the flexible pavement is related to the ability of the pavement to sustain the accumulated strain in the pavement structure through the design life of the pavement and it is considered as a good measure of its fatigue life. In the present work, asphalt concrete mixtures were prepared in the laboratory at optimum binder content and compacted in a slab mold using the roller compaction. Beam specimens of 62 mm width, 56 mm depth, and 400 mm length; were obtained from the prepared asphalt concrete slab samples. The beam specimens were tested for fatigue under repeated flexural stresses at 20℃ environments following the constant strain mode of loading. Constant strain modes of three levels have been tried as target amplitude, (750, 400, and 250) microstrain and the implemented loading frequency was 5 Hz throughout the test. The viscoelastic properties of asphalt concrete specimens have been monitored, analysed, and compared. It was noticed that the phase angle of asphalt concrete rises at failure by (33.3 and 50) % when the constant strain level rises from 250 to 400 and 750 respectively. However, the cumulative dissipated energy of asphalt concrete specimens increases at failure by (10 and 24) folds when the constant strain level declines from 750 to 400 and 250 respectively. On the other hand, the fatigue life of asphalt concrete specimens was (6.1 and 141.8) folds higher than that of 750 constant strain level for specimens practicing 400 and 250 constant strain levels respectively. It was revealed that higher constant strain level can exhibit sharper trend of decline in its initial stiffness as compared with the other microstrain levels.
Modeling the Thermal Behavior of the Viscoelastic Properties of Asphalt Concrete
Britain International of Exact Sciences Journal (BIoEx-Journal), 2022
The viscoelastic properties of asphalt concrete are susceptible to the variation in the pavement temperature. In the present work, asphalt concrete beam specimens were prepared at optimum binder content and tested under repeated flexural stresses for fatigue life. Three testing temperature were implemented (5, 20, and 30) ℃. The variation in the phase angle, dissipated energy, flexural stiffness, and permanent deformation due to the testing temperatures were monitored and modeled. It was concluded that the viscoelastic properties of asphalt concrete are highly sensitive to the variation in testing temperature. The phase angle and the permanent deformation increases sharply as the testing temperature rises. However, the dissipated energy and the flexural stiffness declines as the testing temperature rise. Mathematical models were obtained which can be implemented in identifying the thermal behavior of the viscoelastic properties of asphalt concrete.