Modelling of Pavement Materials –Numerical and Experimental Aspects (original) (raw)
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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.
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 ...
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.
A better understanding of asphalt concrete response
The necessity of realistic non-linear, three-dimensional material modeling for asphalt concrete is demonstrated by using such a model to simulate two laboratory tests. For this demonstration the Indirect Tensile Test (ITT) and Semi Circular Bending (SCB) test are used, two relatively simple tests that result in a complicated stress state in the specimen. It becomes quite clear that the observed response can not be modeled without realistic damage descriptions. Prior to these examples of model application the material model used for the simulations is presented and its suitability to describe the response of asphalt concrete is verified. This verification is based on the simulation of laboratory tests used to provide the model parameters.
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...
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.
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...
Journal of Applied Polymer Science, 2008
Scientists and engineers are constantly trying to improve the performance of asphalt pavements. Modification of the asphalt binder is one approach taken to improve pavement performance. The idea of using fibers to improve the behavior of materials is an old suggestion, so different researchers reported the results of adding a large variety of fibers to asphalt concrete (AC) as fiber-reinforced asphalt concrete (FRAC). However, there are few comments about the mechanism of reinforcement and fiber performance in the inner structure of AC and/or exposing some models to predict fiber recital as a modifier in FRAC. So this article is going to introduce two simple models for predicting FRAC behavior during longitudinal loads. The former is called ''Slippage Theory'' and the lat-ter is ''Equal Cross-Section.'' Finally, four types of fibers (glass, nylon 6.6, polypropylene, and polyester) were used in AC to evaluate the two theories. ''Marshall Test,'' as stability and flow outcomes, and ''Specific Gravity'' were carried out on specimens in the next stages followed by an artificial neural network (ANN), which was developed in the system to recognize important fiber parameters effective in the FRAC specifications. In the end, the two theories predicted each fiber performance in FRAC as well as ANN.
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).