A framework for linear viscoelastic characterization of asphalt mixtures (original) (raw)
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On Viscoelastic Properties of Asphalt Mixtures
2017
Dragan T. Spasić 1, UDK: 691.16:539.3:517.965 DOI:10.14415/konferencijaGFS2017.039 Summary: This paper comprises the fractional Kelvin-Zener model of viscoelastic body, the Laplace transform and a least squares method, all applied in creep/recovery testing of asphalt mixtures for the purpose of parameter identification. The parameters describing viscoelastic properties of these mixtures are: the order of the fractional derivative, modulus of elasticity, as well as two relaxation constants that obey restrictions that follow from the second law of thermodynamics. Knowing these four parameters one may predict the behavior of an asphalt mixture for different loads. Besides, the pattern of change of these parameters may be related to alterations of the viscoelastic properties of an asphalt mixture due to either aging or different environmental conditions.
Linear viscoelasticity was strictly differentiated from the nonlinearity. Material properties in linear viscoelastic stage were the reference properties. Viscoelastic stress, reference modulus & pseudostrain were rigorously established. The sole linear viscoelastic effect was eliminated to determine pseudostrains. Dissipated pseudostrain energies were determined for representative loading cycle. a b s t r a c t It has been demonstrated that asphalt mixtures experienced linear viscoelastic stage, nonlinear viscoelas-tic stage and damage stage when subjected to controlled-strain repeated direct-tension (RDT) tests with increasing strain levels. However, the linear viscoelastic properties of asphalt mixtures are usually muddled up with their nonlinear viscoelastic properties. These confusions directly lead to the incorrect determination of the pseudostrains and dissipated pseudostrain energies (DPSEs) in the nonlinear viscoelastic stage and damage stage. This study investigated the material properties of fine aggregate mixture (FAM) specimens in all three stages. These three stages were differentiated and characterized in terms of the viscoelastic stress, pseudostrain and DPSE. The definitions of viscoelastic stress, reference modulus and pseudostrain were rigorously established to assure that the material properties in the linear viscoelastic stage were the reference properties and that the sole linear viscoelastic effect was eliminated when determining the pseudostrain and DPSE in the three stages. The characteristics of the DPSE in the three stages were found to be: (1) the DPSE of any loading cycle was zero in the linear viscoelastic stage; (2) in the nonlinear viscoelastic stage, the DPSE of each loading cycle remained approximately the same with the growth of the number of loading cycles, and the DPSE increased to a larger value when the strain level of the RDT test increased to a higher level; (3) in the damage stage, the DPSE of the loading cycle increased as the number of loading cycles increased. This study strictly distinguished the linear viscoelas-ticity from the nonlinear viscoelasticity of the asphalt mixtures, which is critical for the accurate determination of the DPSE spent in overcoming the nonlinear viscoelasticity and in developing damages, such as cracking and permanent deformation, in the asphalt mixtures.
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.
2013
The dynamic modulus IE*I is the primary input material property of asphalt mixtures for the asphalt pavement design procedures based on mechanistic principles. Among other factors, this dynamic modulus is a function of temperature and loading frequency. In order to model the effects of these factors, the dynamic modulus of the asphalt mixture is described using a master curve constructed at a given reference temperature on the basis of the principle of frequency-temperature superposition for thermo-rheologically simple materials. The amount of shifting at each temperature is given by a shift factor that describes the temperature dependency of the material. Different methods and mathematical functions have been proposed to model these shift factors and the resulting dynamic modulus master curve. The objective of this paper is to evaluate these various methods and mathematical equations that can be satisfactorily used for modelling the dynamic modulus IE*I master curves, as a function...
Open Journal of Civil Engineering, 2015
The main purpose of this article is to choose among advanced rheological models used in the French rational design, one that best represents the viscoelastic behavior of asphalt mixtures mixed with aggregates of Senegal. The model chosen will be the basis for the development of computational tools for stress and strain for Senegal. However, the calibration of these models needs complex modulus test results. In opposition to mechanical models the complex modulus can directly characterize the viscoelastic behavior of bituminous materials. Here determination is performed in the laboratory by using several types of tests divided into two groups: homogeneous tests and non-homogeneous tests. The choice of model will be carried out by statistical analysis through the least squares method. To this end, a study was carried out to "Laboratory of Pavement and Bituminous Materials" (LCMB) with asphalt concrete mixed with aggregate from Senegal named basalt of Diack and quartzite of Bakel. In this study, the test used to measure the complex modulus is the Canadian test method LC 26-700 (Determination of the complex modulus by tension-compression). There mainly exist two viewing complex modulus planes for laboratory test results: the Cole and Cole plane and the Black space. The uniqueness of the data points in these two areas means that studied asphalt concretes are thermorheologically simple and that the principle of time-temperature superposition can be applied. This means that the master curve may be drawn and that the same modulus value can be obtained for different pairs (frequency-temperature). These master curves are fitted during the calibration process by the advanced rheological models. One of the most used software in the French rational design for the visualization of complex modulus test results and calibration of rheological models developed tools is named Visco-analysis. In this study, its use in interpreting the complex modulus test results and calibration M. L. C. Aidara et al. 290 models shows that, the studied asphalt concretes are thermorheologically simple, because they present good uniqueness of their Black and Cole and Cole and Black diagrams. They allow a good application of the principle of time temperature superposition. The statistical analysis of calibration models by the least squares method has shown that the three studied models are suitable for modeling the linear viscoelastic behavior of asphalt mixtures formulated with the basalt of Diack and the quartzite of Bakel. Indeed their calibration has very similar precision values of "Sum of Squared Deviation" (SSD) about 0.185. However, the lower precision value (0.169) is obtained with the 2S2P1D model.
A two-constituent nonlinear viscoelastic model for asphalt mixtures
Road Materials and Pavement Design, 2019
The goal of this study is to model the creep and recovery response of fine asphalt mixtures using a thermodynamically consistent nonlinear viscoelastic model. The model considers asphalt mixture to consist of two constituents: aggregate structure incorporating the asphaltaggregate interface and asphalt binder. The efficacy of the model is evaluated using the response of warm fine aggregate mixtures (WFAM). These materials were produced using a polymer-modified binder of PG 76-22 and three warm mix additives (Sasobit, Advera and Rediset). Unaged and aged samples were subjected to creep stress levels of 75 and 400 kPa followed by rest periods. The model was quite successful in capturing the material behaviour as a single set of parameters were derived from the prediction of shear and normal stress responses for both 75 and 400 kPa stress levels. The presented model offers a unique feature in modelling the energy storage and dissipation of each of the two constituents. As such, one can examine the effect of changes in individual material properties on the material response and performance.
Mechanics of Time-Dependent Materials, 2011
This paper presents a simple and practical approach to obtain the continuous relaxation and retardation spectra of asphalt concrete directly from the complex (dynamic) modulus test data. The spectra thus obtained are continuous functions of relaxation and retardation time. The major advantage of this method is that the continuous form is directly obtained from the master curves which are readily available from the standard characterization tests of linearly viscoelastic behavior of asphalt concrete. The continuous spectrum method offers efficient alternative to the numerical computation of discrete spectra and can be easily used for modeling viscoelastic behavior. In this research, asphalt concrete specimens have been tested for linearly viscoelastic characterization. The linearly viscoelastic test data have been used to develop storage modulus and storage compliance master curves. The continuous spectra are obtained from the fitted sigmoid function of the master curves via the inverse integral transform. The continuous spectra are shown to be the limiting case of the discrete distributions. The continuous spectra and the time-domain viscoelastic functions (relaxation modulus and creep compliance) computed from the spectra matched very well with the approximate solutions. It is observed that the shape of the spectra is dependent on the master curve parameters. The continuous spectra thus obtained can easily be implemented in material mix design process. Prony-series coefficients can be easily obtained from the continuous spectra and used in numerical analysis such as finite element analysis.
Uniqueness of the Viscoelastic Time-Function for Asphalt-Aggregate Mixes
International Conference on Advanced Characterisation of Pavement and Soil Engineering Materials, 2007
In general mechanical terms asphalt-aggregate mixes are both viscoelastic and viscoplastic at service temperatures and loading conditions. The focus of this paper is on the viscoelastic component-response under small-strains. This research is part of an ongoing effort by the authors to develop a 3-D constitutive model for asphalt mixes. The paper presents laboratory tests consisting of creep and recovery cycles under uniaxial and isotropic stress conditions. Using a special load-transfer device and employing advanced triaxial testing procedures it was possible to obtain fast unloading after each creep period and insure true zero-stress during recovery times. These features enabled a reliable and straightforward isolation of the viscoelastic response from the total deformation. Analysis of the test data shows that one unique creep-compliance function may be used to describe the viscoelastic response of the material under multiaxial stress conditions. This finding will greatly simplify any future development and calibration of a 3-D material-model.
Materials
Dynamic modulus master curves are usually constructed by using sigmoid functions, but the coefficients of these functions are not independent of each other. For this reason, it is not possible to clearly identify their physical mean. Another way of describing the dynamic modulus master curves is to choose the Ramberg-Osgood (RAMBO) material model, which is also well-suited for modelling the cyclic behaviour of soils. The Ramberg-Osgood model coefficients are completely independent of each other, so the evaluation of the fitted curve is simple and straightforward. This paper deals with the application of the Ramberg-Osgood material model compared to the usual techniques for constructing a master curve, determining the accuracy in describing the material behaviour of asphalt mixtures, and seeking any surplus information that cannot be derived by traditional techniques. Because the dynamic modulus and phase angle master curves are strictly related, in the present study, the asymmetric ...
Obtaining and modeling the relaxation modulus of self-healing asphalt mixtures
FIRAT UNIVERSITY JOURNAL OF EXPERIMENTAL AND COMPUTATIONAL ENGINEERING, 2022
In this study, pure and self-healing asphalt mixture samples were obtained by adding capsules containing waste vegetable oil to mixtures at 0.25, 0.50, 0.75 and 1.00% ratios. Afterwards, creep test with a constant stress was carried out on the samples, and the resistance of asphalt mixtures against permanent deformation was investigated. Relaxation modulus values were obtained by using the creep compliance values that measured at the end of the experiment with mathematical transformations. Then, the relaxation modulus results were fitted to the Generalized Maxwell Model, which is a common model used to represent the viscoelastic properties of asphalt mixtures, and Prony series parameters were obtained. The results showed that the addition of capsule reduced the permanent deformation strength of the asphalt mixture. In addition, the curve fitting processes were successfully performed and the desired parameters were obtained with high accuracy.