A better understanding of asphalt concrete response (original) (raw)

Asphalt Concrete Response: experimental determination and finite element implementation

ABSTRACT: At the previous conference the beginning of an extensive experimental and analytical investigation into the mechanisms leading to the initiation and propagation of damage in asphalt concrete pavements was reported. The objectives of this Asphalt Concrete Response (ACRe) project were twofold, firstly a 3-dimensional, strain rate sensitive, temperature and loading history dependent constitutive model would be formulated and implemented in the finite element package CAPA-3D. Secondly, the necessary experimental set-ups, testing procedures and data-analysis methods for determination of the model parameters would be developed. At the time the prototype formulation of the model was reported, along with preliminary test results and the way in which the model parameters were determined on the basis of the experimental results. A simulation of the dynamic non-linear response of a pavement was included to demonstrate the possibilities of the approach. In the past years, the project ...

Modelling of Asphalt Concrete - Numerical and Experimental Aspects

Recent Advances in Materials Characterization and Modeling of Pavement Systems, 2003

Some results of an extensive experimental and numerical research project on the response of Asphalt Concrete (AC) are presented. In the project, a material model for AC is being developed and implemented in the Finite Elements package CAPA-3D. Also, the test setups , instrumentation, and test procedures necessary to characterise the material and determine the model parameters were developed. In an early stage of the project, it was recognised that failure in tension and compression followed a different mechanism and needed to be described separately in order to capture the response to alternating loads. From the results of uniaxial tension tests it became apparent that also in tension pronounced non-linearity occurred prior to the peak load. The adaptations necessary to incorporate this in the model are presented in this paper. The response predicted by the model relations is compared to that observed in laboratory tests to validate the model relations and it can be seen that the observed behaviour is described quite well by the model.

Issues in the Constitutive Modeling of Asphalt Concrete

Several aspect of the development and implementation of a three dimensional, inelastic constitutive model for asphalt concrete are presented. Attention is focussed on the inherent differences between tension and compression damage and the way this is accounted for in the model. On the basis of laboratory tension tests it is shown that also in tension non-linear response can be observed prior to the peak. A complete overview of the model relations is presented and examples of model verification are included. Finally, the indirect tension test is modelled and the predicted response is compared to laboratory results. It is concluded that for the specific laboratory tests that were simulated, a significant amount of energy is expended in the loading regions.

3D Finite Element Model for Asphalt Concrete Response Simulation

An extensive experimental, analytical and numerical investigation on the response of asphalt concrete is currently in progress at Delft University of Technology. The objectives of this Asphalt Concrete Response (ACRe) project are: (a) the formulation and finite element implementation of a 3-dimensional, strain rate sensitive, temperature and loading history dependent constitutive model, (b) the development of the necessary experimental set-ups, testing procedures and data-analysis methods for determination of the model parameters. These objectives are strongly interrelated: on the one hand the model dictates what should be measured in a test, while on the other hand, the response observed in the tests sets the requirements for the model. As a result, model development/verification and experimental testing have been progressing in parallel throughout the project. In this contribution both, the finite element and the experimental aspects of the project will be presented. The constitut...

Modeling of the Asphalt Concrete to Compare Uniaxial, Hollow Cylindrical, and Indirect Tensile Test

International journal of pavement research and technology, 2014

The objective of this study is to develop a micromechanical based Discrete Element Model (DEM) to simulate dynamic modulus of the asphalt concrete using Uniaxial Tensile (UT), Hollow Cylindrical Tensile (HCT), and Indirect Tensile (IDT) model. This research is used to compare DEM simulation of the UT, HCT, and IDT tests. The asphalt concrete mixture used was a 19 mm Nominal Maximum Aggregate Size (NMAS) with an asphalt content of 5.59% and air void level of 4.36% to develop UT, HCT, and IDT model. The dynamic moduli of the sand mastic and stiffness of aggregate were used as input parameters of the DEM to predict the dynamic moduli of the asphalt concrete through a virtual testing of UT, HCT, and IDT. The sand mastic had an NMAS of 1.18mm, which was used in a DEM. The three-dimensional (3D) internal microstructure of the asphalt concrete mixture (i.e., distribution of aggregate, mastic, and air voids) was obtained through the X-ray CT (Computed Tomography). From the 3D X-ray CT image...

Modelling of Pavement Materials –Numerical and Experimental Aspects

Results of an extensive experimental and numerical research project on the response of Asphalt Concrete (AC) are presented. In the projects a material model for AC is being developed and implemented in the Finite Elements package CAPA-3D. Also, the test set-ups, instrumentation and test procedures necessary to characterise the material and determine the model parameters were developed. In an early stage of the project it was recognised that failure in tension and compression followed a different mechanism and needed to be described separately in order to capture the response to alternating loads. From the results of uniaxial tension tests it became apparent that also in tension a pronounced non-linearity occurred prior to the peak load. The adaptations necessary to incorporate this in the model are presented in this paper. The response predicted by the model relations is compared to that observed in laboratory tests to validate the model relations and it can be seen that the observed behaviour is described quite well by the model.

The effect of strain rate on asphaltic concrete response

An important factor influencing the compressive and the tensile strength of asphaltic materials is the strain rate. In this contribution, some theoretical ambiguities regarding the definition of an objective measure for strain rate are discussed. A triaxial constitutive model for strain rate sensitive asphaltic concrete has been utilized to simulate the nonlinear response of the material. In order to illustrate the effect of the definition of strain rate, finite element simulations were compared on the basis of the Indirect Tension Test (ITT).

the multiaxial test - asphalt concrete response (ACRe)

In the Asphalt Concrete Response (ACRe) project, a three dimensional, non-linear material model for Asphalt Concrete is being developed. This model, which is based on the flow surface proposed by Desai, describes three types of material response, namely: elasticity, visco-plasticity and cracking. In the ACRe project also the test set-ups and procedures necessary for the model parameter determination are being developed. This requires an extensive test program, in which firstly the uniaxial compression test and secondly the uniaxial tension set-up were developed. Finally, the confinement sensitivity of the material needs to be investigated and for that purpose the multiaxial test set-up described in this report was developed.

Stress-Strain and Failure Modes of Asphalt Concrete in Compression Due to Geometrical Changes

Proceedings of the 16th LACCEI International Multi-Conference for Engineering, Education, and Technology: “Innovation in Education and Inclusion”, 2018

The stress-strain relationship of materials is used to predict their performance during service. This paper presents an evaluation of asphalt concrete modes of failure and describes the stress-strain relationship that governs the material beyond the limit of elasticity. The relationship of stress-strain is identical to that of cement concrete in compression. The experiments used short term static compression loading on cylindrical and prismatic asphalt concrete specimens. The effects of mixture types, specimen shape, height, temperature, binder type and testing orientation were investigated. The key parameters of the stress-strain curve were determined and used in assessing the failure mode, were: unconfined compressive strength, the strain at peak stress, initial tangent modulus and fracture energy. The tests revealed that cube specimens tested parallel to the direction compacted, achieved higher compressive strength than specimens tested perpendicular to the direction compacted. Similar strain at peak stress was obtained for both loading directions. An increase in height in cylindrical specimens, resulted in a decrease in compressive strength and strain at peak stress. Cylindrical specimens had greater stiffness than prismatic specimens with similar aspect ratios. Specimens at higher temperatures attained lower compressive strength. The study also showed that temperature has significant influence on the initial tangent modulus and fracture energy. The higher the temperature, the lower the initial tangent modulus and the fracture energy. There were significant changes in the peak stress and strains between the asphalt concrete mix types. The parameters derived can and have been used for inputs in finite element programs to model the laboratory and field behavior of different asphalt concrete mixtures used in pavement structures.

CONSTITUTIVE RELATIONS FOR ASPHALT CONCRETE UNDER HIGH RATES OF LOADING

A main characteristic of asphalt concrete (AC) is its tendency to behave elastically and viscoplastically during cold and hot seasons, respectively. An understanding of the mechanical behaviour of AC under various loading conditions is crucial to a more rational design of flexible pavements and requires more elaborate and comprehensive constitutive relations for AC. In this paper, AC behaviour under high rates of loading has been experimentally studied using uniaxial, triaxial compression and pavement simulation tests. The loading matrix followed in the testing program consisted of 0.05, 0.1 and 0.2 seconds loading durations, three stress levels of 207, 414, and 827 kPa, and three temperatures of 25, 35 and 41 0 C. The experimental results indicated that AC materials display an elastic/viscoplastic response under uniaxial stress pulses. The viscoplastic response was characterized by the rate dependency of the plastic response and was found to be linearly strain hardening. The results revealed that the yielding point is dependent on the strain rate and temperature and increases as both variables increase. The developed model uses a yield criterion based on the loading function defined by Drucker-Prager. The uniaxial material properties were calibrated to field conditions from the pavement simulation test data through an optimization process that involved iterative calls between finite element results and the optimum parameters, which were obtained using ABAQUS and CONMIN, respectively. This analysis resulted in the development of a generalized elastic/viscoplastic constitutive relation form AC for the testing conditions.