Jiupeng Zhang

Development and Validation of Viscoelastic-Damage Model for Three-Phase Permanent Deformation of Dense Asphalt Mixture

AbstractPermanent deformation of asphalt mixture under repeated load can be divided into three phases: decelerating phase, stationary phase, and accelerating flow phase. Most of the existing models cannot fully describe deformation characteristics during the three phases. In this paper, the characteristics of three-phase permanent deformation are considered as the results of a competition between damage and hardening, in which a damage variable and a hardening variable are introduced to modify Burger’s model. First, the series-wound dashpot of the Burger’s model is modified by Usan’s hardening variable, and the undamaged viscoelastic properties are derived from rheological theory. Secondly, Kachanov’s equation for damage evolution is adopted to establish the constitutive model by using Lemaitre’s effective stress principle. Then a repeated load consisting of a haversine loading period and rest period is employed to simulate the actual vehicle loading on the asphalt pavement. Third, a viscoelastic-damage m...

Multiscale Validation of the Applicability of Micromechanical Models for Asphalt Mixture

Asphalt mixture is more complicated than other composite materials in terms of the higher volume fraction of aggregate particles and the viscoelastic property of asphalt matrix, which obviously affect the applicabilities of the micromechanical models. The applicabilities of five micromechanical models were validated based on the shear modulus of the multiscale asphalt materials in this paper, including the asphalt mastic, mortar, and mixture scales. It is found that all of the five models are applicable for the mastic scale, but the prediction accuracies for mortar and mixture scales are poorer. For the mixture scale, all models tend to overestimate at the intermediate frequencies but show good agreement at low and high frequencies except for the Self-Consistent (SC) model. The Three-Phase Sphere (TPS) model is relatively better than others for the mortar scale. The applicability of all the existing micromechanical models is challenged due to the high particle volume fraction in the multiscale asphalt materials as well as the modulus mismatch between particles and matrix, especially at the lower frequencies (or higher temperatures). The particle interaction contributes more to the stiffening effect within higher fraction than 30%, and the prediction accuracy is then deteriorated. The higher the frequency (or the lower the temperature) is, the better the model applicability will be.

Effects of material characteristics on asphalt and filler interaction ability

ABSTRACT Asphalt and filler interaction plays a key role on the performances of asphalt mastics and mixtures, while the asphalt and filler interaction ability is in turn affected by the material characteristics. In order to analyse the effects of material characteristics on asphalt and filler interaction, two kinds of matrix asphalt binders and three kinds of fillers were used to prepare asphalt mastics with different filler volume fractions. The dynamic shear rheological properties of these asphalt mastics were measured. The evaluation index K–B–G * was calculated subsequently to analyse the effects of material characteristics on the asphalt and filler interaction ability. The results show that filler volume fraction, filler particle size, SiO2 content and asphalt components had various levels of effects on the asphalt and filler interaction ability. Variance analysis was then conducted to rank these influencing factors from high to low as: (1) filler particle size, (2) asphaltene and resins content, (3) filler volume fraction, and (4) SiO2 content.

Effects of WMA Additive on the Rheological Properties of Asphalt Binder and High Temperature Performance Grade

Sasobit additives with different dosages were added into 70# and 90# virgin asphalt binders to prepare WMA binders. The rheological properties, including and δ, were measured by using DSR at the temperature ranging from 46°C to 70°C, and the effects of temperature, additive dosage and aging on , critical temperature, and H-T PG were investigated. The results indicate that WMA additive improves but reduces δ, and the improvement on 70# virgin binder is more significant. exponentially decreases with the increasing temperature but linearly increases with the increasing additive dosage. Aging effect weakens the interaction between binder and additive but significantly increases the binder’s viscosity; that is why is higher after short-term aging. In addition, the critical temperature increases with the increasing additive dosage, and the additive dosage should be more than 3% and 5% to improve H-T PG by one grade for 70# and 90# virgin binder, respectively.

Evaluation of Nano-ZnO Dispersed State in Bitumen with Digital Imaging Processing Techniques

Nano-ZnO can be used as the tracer material to mark the asphalt, and the dispersion of nano-ZnO in the asphalt has an important impact on the mark effect; thus, it is important to study the dispersion state of nano-ZnO in asphalt. In order to achieve this goal, a method of sample preparation to make the nano-ZnO particle exposed to the asphalt surface, and a method for evaluating the dispersion state of nano-ZnO based on digital image processing technique, were put forward in this paper. In this quantitative evaluation system, scanning electron microscope and IPP software were used to scan the sample and output data; area ratio variation coefficient, number variation coefficient, and average particle size of nano-ZnO particle were used to evaluate the dispersion of nano-ZnO. Besides that, through the research of the dispersion state, the optimal dispersion conditions of nano-ZnO in asphalt were found out in this paper.

Organic Montmorillonite Modified Asphalt Materials: Preparation and Characterization

Organic montmorillonite (OMMT) modified asphalt was prepared with the melting intercalation technology. The distribution of OMMT layers in matrix asphalt was characterized through x-ray diffraction (XRD) and transmission electron microscope (TEM), and the effect of OMMT on physical properties and dynamic rheology of matrix asphalt were studied as well. It was found that OMMT homogeneously dispersed in the modified asphalt and intercalated OMMT/asphalt nanocomposites were prepared by means of melt extrusion. Additionally, from the penetration, softening point, and dynamic shear rheometer (DSR) testing result, it was observed that the OMMT obviously improved the high-temperature stability, temperature serviceability, and rut resistance of the matrix asphalt. The bending beam rheometer (BBR) results indicated that the OMMT modified asphalt with OMMT dosage of 3 % exhibited the lowest stiffness and highest resistance to low temperature cracking, and had less effect on the relaxation of stress in low temperature in comparison with OMMT modified asphalt with OMMT dosage of 1 % and 5 %. Furthermore, it was found that the optimal dosage of OMMT was 3 %.

Evaluation of aggregate gradation and distributing homogeneity based on the images of asphalt mixture

In order to quantitatively evaluate aggregate gradation and distributing homogeneity in asphalt mixture, digital image processing techniques were used to obtain the two-dimensional gradation characteristics in several cross-sections of the coring specimen, and the stereoscopy theory was applied to reconstruct the three-dimensional gradation characteristics, which was compared with the actual gradation, and a correction factor was deduced. It is found that the relative error between corrected and actual aggregate gradation is less than 5%. Then, the aggregated distributing information in horizontal and vertical sections were analysed to establish the horizontal and vertical distributing homogeneity indexes, respectively. The horizontal distributing homogeneity can be evaluated by the variation of inertia of the X-axis, Ix, during rotating, and the vertical distributing homogeneity can be evaluated by the statistical index of the aggregate centroids, Sa. The smaller the Ix variation, the better the horizontal distributing homogeneity. The larger the Sa, the better the vertical distributing homogeneity.

Nonlinear viscoelastic model for asphalt mixture subjected to repeated loading

The modified Burgers model was selected to develop the nonlinear viscoelastic (NLVE) model of asphalt mixture subjected to repeated load, and the permanent strain was expressed as the summation of residual viscoelastic (RVE) and nonlinear viscous (NLV) strains. It is found that RVE and NLV strains increase with the increasing loading cycles, but RVE strain decreases with the increasing rest period while NLV is not related to the rest period. The proportion of NLV strain to total strain increases with the rest period and loading cycles and the NLV strain is the predominant part if the rest period is long enough. Thus, the NLVE model could be predigested. The repeated load permanent deformation tests of three asphalt mixtures were conducted at different temperatures and stresses for model validation and parameter analysis. It is found that the permanent strain increases with test temperature and stress and the proposed NLVE model can well describe the mechanical behaviour of the asphalt mixture subjected to repeated load. Moreover, fitting results show that the modified Burgers model parameters , and decrease with test temperature but increase with stress while parameter shows no significant change rule.

Aging Kinetics Characteristics of Warm Mix Asphalt Binder using Softening Point and N-pentane Asphaltene Content as the Parameters

This paper presented research on the aging kinetics characteristics of asphalt binder by using softening point and n-pentane asphaltene content, respectively, as parameters. Sasobit additives were added into two matrix asphalt binders to prepare the warm mix asphalt binders, and then were aged at different temperatures and time. The softening points and contents of n-pentane asphaltene were measured. Results indicated that the softening point was improved by adding the additives. Both the softening point and content of n-pentane asphaltene increased with aging temperature and aging time, and the increments of matrix asphalt binders were bigger. Taking the softening point and content of n-pentane asphaltene as the parameters, respectively, the aging kinetics models were established, and the reaction rate constants and reaction activation energies were calculated. It was found that warm mix asphalt binders had lower reaction constants and bigger reaction activation energies, that is to say the anti-aging property of warm mix asphalt was better. The anti-aging properties could be better evaluated by the aging kinetics models based on the softening point for its higher accuracy and testing convenience.

Effects of Emulsifier Dosage and Curing Time on Self-Healing Microcapsules Containing Rejuvenator and Optimal Dosage in Asphalt Binders

Micro-damages always occur and accumulate in asphalt pavement materials under the effects of temperature, vehicle loads and other factors during service. Accordingly, self-healing microcapsules could be added into asphalt binder and repair micro-damages to prevent damage extension in time. In this study, the emulsified rejuvenator and melamine-urea-formaldehyde resin (MUF) were selected as the core and cyst wall materials, respectively, and in-situ polymerization method was applied to synthesize the novel microcapsules. The effects of emulsifier dosage and curing time were revealed on the particle size, dispersion, surface morphology and coating properties, and the optimum process parameters were determined for microcapsules. Then, the micro morphology, molecular structure, and thermal stability were further investigated to determine the optimal preparation of the microcapsules. Finally, the linear amplitude sweep (LAS) test was performed to evaluate the self-healing efficiency of the asphalt binder with different dosages of prepared microcapsule, and the optimal dosage of microcapsules was determined as 0.5%.