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Ali Khodaii - One of the best experts on this subject based on the ideXlab platform.

  • comparison of tensile and compressive Relaxation Modulus of asphalt mixes under various testing conditions
    Materials and Structures, 2016
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    Mode of loading, i.e., tension and compression, is an important factor that affects the Relaxation Modulus of asphalt mixtures. A laboratory experiment was conducted to compare the relative variations of tensile and compressive Relaxation Modulus master curves of dense graded asphalt mixes under various testing conditions including mix characteristics, aging condition, and temperature. Crushed stone aggregates having two gradations, and 60/70 penetration asphalt binder with two binder contents were selected to fabricate the asphalt mixture specimens at two air void levels and three aging conditions with three replicates for each experimental combination. Direct tension/compression Relaxation Modulus tests were carried out on the specimens at four temperatures using the trapezoidal pattern at a low level of input strain. Tensile and compressive Relaxation Modulus master curves were constructed for all the experimental combinations using the sigmoidal fitting model together with the numerical temperature shifting technique. Sigmoidal model coefficients of α, β, and γ were chosen, as representatives of Relaxation Modulus master curves, to be compared between tension and compression. Based on the graphical representations as well as the overall mean values calculated for the ratios of tensile–compressive coefficients under various testing conditions, it was concluded that tensile and compressive behavior of asphalt mixes may be generally different to each other. Both the tensile α and γ coefficients may always be higher than those obtained in compression for all the testing conditions. In addition, the β coefficient obtained in tension may be lower than the compressive one only for the shorter aging times as well as the higher reference temperatures; while this coefficient in tension may be higher than the compressive one for the other testing conditions. In addition, analyses of variance showed that the factors of binder content and air void level may have the most significant effects on the ratios of tensile–compressive α and γ coefficients, respectively; while the reference temperature may be the most inflectional factor on the ratio of tensile–compressive β coefficients.

  • Predicting the tensile Relaxation Modulus of asphalt mixes based on the mix design and environmental factors
    International Journal of Pavement Engineering, 2015
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    AbstractThe main objective of this study was to predict the tensile Relaxation Modulus of asphalt mixes, without having to perform the common Relaxation Modulus tests, by developing a predictive model based on the mix characteristics, ageing condition, temperature and loading time. To this end, cylindrical asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels and three ageing conditions with four replicates. Uniaxial tensile Relaxation Modulus tests were conducted on the specimens at four temperatures using the trapezoidal loading pattern at a low level of strain. Tensile Relaxation Modulus master curves of all the experimental combinations were constructed by the sigmoidal model. Statistical analysis of variance and regression analysis was performed on the test data and a predictive model was developed. Finally, the predictive model was verified using a group of measured ...

  • An investigation of different fitting functions to accurately model the compressive Relaxation Modulus master curve of asphalt mixes
    Road Materials and Pavement Design, 2015
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    This research was carried out to rank the different fitting functions utilised to construct the compressive Relaxation Modulus master curve of asphalt mixes. To this end, 72 cylindrical dense-graded asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels, and three ageing conditions with three replicates for each experimental combination. Uniaxial compressive Relaxation Modulus tests were conducted on the specimens at four temperatures using the trapezoidal loading pattern at a low level of input strain. Different functions, that is, Pure Power Law (PPL), Generalised Power Law (GPL), Modified Power Law (MPL), Modified Power Law Series (MPLS), Standard Sigmoid (SS), Generalised Logistic Sigmoid (GLS), and Prony Series (PS), were utilised as the fitting models, and the compressive Relaxation Modulus master curves of all the experimental combinations were constructed using the ...

  • Development of a predictive model for the compressive Relaxation Modulus of asphalt mixtures
    Road Materials and Pavement Design, 2015
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    Relaxation Modulus as an important viscoelastic property of asphalt mixes is usually determined using time-consuming and expensive test methods. Therefore, this research was carried out to develop a predictive model for the time-dependent compressive Relaxation Modulus of asphalt mixtures based on the mix specifications, volumetric properties, ageing condition, and temperature. To this end, crushed stone aggregates together with 60/70 penetration asphalt binder (corresponding to PG 64-22) were used to prepare the asphalt mixture specimens at two aggregate gradations, two binder contents, two air void levels, and three ageing conditions with four replications. Direct compression Relaxation Modulus tests were conducted at four different temperatures, and the sigmoidal model was used together with the numerical temperature-shifting technique to construct the compressive Relaxation Modulus master curves for all the experimental combinations. Statistical analysis of variance and regression analysis were then p...

  • Comparing various fitting models to construct the tensile Relaxation Modulus master curve of asphalt mixes
    International Journal of Pavement Engineering, 2014
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    This study was to compare the relative ability of seven common fitting models, i.e. Pure Power Law (PPL), Generalized Power Law (GPL), Modified Power Law (MPL), Modified Power Law Series (MPLS), Standard Sigmoid (SS), Generalized Logistic Sigmoid (GLS) and Prony Series (PS), to construct the tensile Relaxation Modulus master curve of dense graded asphalt mixes. To this end, cylindrical asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels and three ageing conditions with three replicates. Direct tension Relaxation Modulus tests were conducted on the specimens at four different temperatures using the trapezoidal loading pattern at a low level of input strain. Tensile Relaxation Modulus master curves were constructed using all the fitting models together with the numerical shifting technique. Finally, both the graphical and statistical comparisons were made among the fitting...

Joerg Baschnagel - One of the best experts on this subject based on the ideXlab platform.

  • Numerical determination of shear stress Relaxation Modulus of polymer glasses.
    European Physical Journal E, 2017
    Co-Authors: I. Kriuchevskyi, J. P. Wittmer, O. Benzerara, Hendrik Meyer, Joerg Baschnagel
    Abstract:

    Focusing on simulated polymer glasses well below the glass transition, we confirm the validity and the efficiency of the recently proposed simple-average expression $G(t) = \mu_{A}- h(t)$ for the computational determination of the shear stress Relaxation Modulus G(t). Here, $\mu_{A}= G(0)$ characterizes the affine shear transformation of the system at t = 0 and h(t) the mean-square displacement of the instantaneous shear stress as a function of time t. This relation is seen to be particulary useful for systems with quenched or sluggish transient shear stresses which necessarily arise below the glass transition. The commonly accepted relation $ G(t)=c(t)$ using the shear stress auto-correlation function c(t) becomes incorrect in this limit.

  • Simple average expression for shear-stress Relaxation Modulus.
    Physical Review E, 2016
    Co-Authors: J. P. Wittmer, Joerg Baschnagel
    Abstract:

    Focusing on isotropic elastic networks we propose a simple-average expression G(t) = mu(A) - h(t) for the computational determination of the shear-stress Relaxation Modulus G(t) of a classical elastic solid or fluid. Here, mu(A) = G(0) characterizes the shear transformation of the system at t = 0 and h(t) the (rescaled) mean-square displacement of the instantaneous shear stress (tau) over cap (t) as a function of time t. We discuss sampling time and ensemble effects and emphasize possible pitfalls of alternative expressions using the shear-stress autocorrelation function. We argue finally that our key relation may be readily adapted for more general linear response functions.

  • Fluctuation-dissipation relation between shear stress Relaxation Modulus and shear stress autocorrelation function revisited
    Molecular Physics, 2015
    Co-Authors: J. P. Wittmer, O. Benzerara, Joerg Baschnagel
    Abstract:

    The shear stress Relaxation Modulus G(t) may be determined from the shear stress (tau) over cap (t) after switching on a tiny step strain gamma or by inverse Fourier transformation of the storage Modulus G'(omega) or the loss Modulus G `'(omega) obtained in a standard oscillatory shear experiment at angular frequency.. It is widely assumed that G(t) is equivalent in general to the equilibrium stress autocorrelation function C(t) = beta V which may be readily computed in computer simulations (beta being the inverse temperature and V the volume). Focusing on isotropic solids formed by permanent spring networks we show theoretically by means of the fluctuation-dissipation theorem and computationally by molecular dynamics simulation that in general G(t) = G(eq) + C(t) for t > 0 with G(eq) being the static equilibrium shear Modulus. A similar relation holds for G'(omega). G(t) and C(t) must thus become different for a solid body and it is impossible to obtain G(eq) directly from C(t).

Seyed Arash Forough - One of the best experts on this subject based on the ideXlab platform.

  • comparison of tensile and compressive Relaxation Modulus of asphalt mixes under various testing conditions
    Materials and Structures, 2016
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    Mode of loading, i.e., tension and compression, is an important factor that affects the Relaxation Modulus of asphalt mixtures. A laboratory experiment was conducted to compare the relative variations of tensile and compressive Relaxation Modulus master curves of dense graded asphalt mixes under various testing conditions including mix characteristics, aging condition, and temperature. Crushed stone aggregates having two gradations, and 60/70 penetration asphalt binder with two binder contents were selected to fabricate the asphalt mixture specimens at two air void levels and three aging conditions with three replicates for each experimental combination. Direct tension/compression Relaxation Modulus tests were carried out on the specimens at four temperatures using the trapezoidal pattern at a low level of input strain. Tensile and compressive Relaxation Modulus master curves were constructed for all the experimental combinations using the sigmoidal fitting model together with the numerical temperature shifting technique. Sigmoidal model coefficients of α, β, and γ were chosen, as representatives of Relaxation Modulus master curves, to be compared between tension and compression. Based on the graphical representations as well as the overall mean values calculated for the ratios of tensile–compressive coefficients under various testing conditions, it was concluded that tensile and compressive behavior of asphalt mixes may be generally different to each other. Both the tensile α and γ coefficients may always be higher than those obtained in compression for all the testing conditions. In addition, the β coefficient obtained in tension may be lower than the compressive one only for the shorter aging times as well as the higher reference temperatures; while this coefficient in tension may be higher than the compressive one for the other testing conditions. In addition, analyses of variance showed that the factors of binder content and air void level may have the most significant effects on the ratios of tensile–compressive α and γ coefficients, respectively; while the reference temperature may be the most inflectional factor on the ratio of tensile–compressive β coefficients.

  • Predicting the tensile Relaxation Modulus of asphalt mixes based on the mix design and environmental factors
    International Journal of Pavement Engineering, 2015
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    AbstractThe main objective of this study was to predict the tensile Relaxation Modulus of asphalt mixes, without having to perform the common Relaxation Modulus tests, by developing a predictive model based on the mix characteristics, ageing condition, temperature and loading time. To this end, cylindrical asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels and three ageing conditions with four replicates. Uniaxial tensile Relaxation Modulus tests were conducted on the specimens at four temperatures using the trapezoidal loading pattern at a low level of strain. Tensile Relaxation Modulus master curves of all the experimental combinations were constructed by the sigmoidal model. Statistical analysis of variance and regression analysis was performed on the test data and a predictive model was developed. Finally, the predictive model was verified using a group of measured ...

  • An investigation of different fitting functions to accurately model the compressive Relaxation Modulus master curve of asphalt mixes
    Road Materials and Pavement Design, 2015
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    This research was carried out to rank the different fitting functions utilised to construct the compressive Relaxation Modulus master curve of asphalt mixes. To this end, 72 cylindrical dense-graded asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels, and three ageing conditions with three replicates for each experimental combination. Uniaxial compressive Relaxation Modulus tests were conducted on the specimens at four temperatures using the trapezoidal loading pattern at a low level of input strain. Different functions, that is, Pure Power Law (PPL), Generalised Power Law (GPL), Modified Power Law (MPL), Modified Power Law Series (MPLS), Standard Sigmoid (SS), Generalised Logistic Sigmoid (GLS), and Prony Series (PS), were utilised as the fitting models, and the compressive Relaxation Modulus master curves of all the experimental combinations were constructed using the ...

  • Development of a predictive model for the compressive Relaxation Modulus of asphalt mixtures
    Road Materials and Pavement Design, 2015
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    Relaxation Modulus as an important viscoelastic property of asphalt mixes is usually determined using time-consuming and expensive test methods. Therefore, this research was carried out to develop a predictive model for the time-dependent compressive Relaxation Modulus of asphalt mixtures based on the mix specifications, volumetric properties, ageing condition, and temperature. To this end, crushed stone aggregates together with 60/70 penetration asphalt binder (corresponding to PG 64-22) were used to prepare the asphalt mixture specimens at two aggregate gradations, two binder contents, two air void levels, and three ageing conditions with four replications. Direct compression Relaxation Modulus tests were conducted at four different temperatures, and the sigmoidal model was used together with the numerical temperature-shifting technique to construct the compressive Relaxation Modulus master curves for all the experimental combinations. Statistical analysis of variance and regression analysis were then p...

  • Comparing various fitting models to construct the tensile Relaxation Modulus master curve of asphalt mixes
    International Journal of Pavement Engineering, 2014
    Co-Authors: Seyed Arash Forough, Fereidoon Moghadas Nejad, Ali Khodaii
    Abstract:

    This study was to compare the relative ability of seven common fitting models, i.e. Pure Power Law (PPL), Generalized Power Law (GPL), Modified Power Law (MPL), Modified Power Law Series (MPLS), Standard Sigmoid (SS), Generalized Logistic Sigmoid (GLS) and Prony Series (PS), to construct the tensile Relaxation Modulus master curve of dense graded asphalt mixes. To this end, cylindrical asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels and three ageing conditions with three replicates. Direct tension Relaxation Modulus tests were conducted on the specimens at four different temperatures using the trapezoidal loading pattern at a low level of input strain. Tensile Relaxation Modulus master curves were constructed using all the fitting models together with the numerical shifting technique. Finally, both the graphical and statistical comparisons were made among the fitting...

Hua Zheng - One of the best experts on this subject based on the ideXlab platform.

Seakweng Vong - One of the best experts on this subject based on the ideXlab platform.