Viscoelastic Properties Of Asphalt Mixtures Research Articles

Prediction of the fundamental viscoelasticity of asphalt mixtures using ML algorithms

The complex modulus (E*) and phase angle (δ) are fundamental viscoelastic (VE) properties of asphalt material, crucial for pavement performance analysis and modeling. This study presents a novel approach to predict the fundamental VE properties of asphalt mixtures using 20 study mixes with disparate mix design information including different Performance Graded (PG grade) binders, recycled asphalt (RAP) contents, with/without polymer modifications, and mix volumetric properties. By employing the XGBoost model for feature importance analysis, integrating the Bailey method to streamline gradation information, and utilizing master curve shape parameters for modeling, this study has effectively reduced data redundancy and dimensionality. Among four machine learning (ML) models compared, the Multi-Hidden-Layer Backpropagation Neural Network (Multi BP) model demonstrates superior applicability to the asphalt mixture dataset, providing accurate predictions for VE properties at any temperature and frequency combinations. Notably, this predictive model relies solely on the mixture design information as inputs, minimizing the need for laborious laboratory experiments. The developed model can be integrated with Mechanistic-Empirical (ME) design, predicting the variations in rutting and cracking performance of asphalt mixtures over the entire service life. This provides essential foundational input support for long-lasting pavement design.

Application of dynamic complex stiffness modulus master curves of HMA with recycled materials in the mechanistic-empirical design of road pavement structures

The main objective of the paper is to present the possibilities and advantages of advanced methods for determining the viscoelastic properties of asphalt mixtures produced using recycled materials in individual mechanistic-empirical pavement design. The use of various types of materials in asphalt mixture production can significantly alter their functional parameters, such as the dynamic stiffness modulus. In addition, this parameter changes with the change in the temperature of the road pavement and the speed of vehicles. In order to determine the durability of the pavement structure in an informed manner and minimize the risk of error, it is necessary to investigate and describe as precisely as possible this variability in the behavior of asphalt layers as a result of changes in the properties of input materials, e.g. by the addition of recycled materials and under the influence of changes in temperature and load velocity of the pavement. The most effective approach involves the application of master curves of the dynamic complex stiffness modulus of asphalt mixture, constructed based on research results conducted at different temperatures and loading frequencies. This allows for the determination of stress and deformation states of the pavement construction under various climatic conditions, utilizing seasonal or average monthly temperatures and considering the specific characteristics of pavement operation, such as different vehicle speeds for main routes, connectors, or street intersections. The paper compares the changes in dynamic modulus master curves for different types of asphalt mixtures with and without the addition of waste or recycled materials such as reclaimed asphalt pavement (RAP), rubber from used tires, or synthetic fibres and changes impact on the estimated durability of the pavement structure due to different approaches to determining climatic conditions and movement speed.

A Study on the Genetic Algorithm Optimization of an Asphalt Mixture’s Viscoelastic Parameters Based on a Wheel Tracking Test

The generalized Maxwell (GM) constitutive model has been widely applied to characterize the viscoelastic properties of asphalt mixtures. The parameters (Prony series) of the GM are usually obtained via interconversion between a dynamic modulus and relaxation modulus, and they are then input to a finite element model (FEM) as viscoelastic parameters. However, the dynamic modulus obtained with the common loading mode only provides the compressive and tensile properties of materials. Whether the compression or tensile modulus can represent the shear properties of materials related to flow rutting is still open to discussion. Therefore, this study introduced a novel method that integrates the Kriging model into the genetic algorithm as a surrogate model to determine the viscoelastic parameters of an asphalt mixture in rutting research. Firstly, a wheel tracking test (WTT) for AC-13 was conducted to clarify the flow rutting development mechanism. Secondly, two sets of the AC-13 viscoelastic parameters obtained through the optimization method and the dynamic modulus were used as inputs into the FEM simulation of the WTT to compare the simulation results. Finally, a sensitivity analysis of viscoelastic parameters was performed to improve the efficiency of parameter optimization. The results indicating the viscoelastic parameters obtained by this method could precisely characterize the development law of flow rutting in asphalt mixtures.

Predicting asphalt mixture fatigue life via four-point bending tests based on viscoelastic continuum damage mechanics

A more technically accurate approach to predict fatigue life of asphalt mixtures can enhance the precision of performance evaluation for asphalt pavements. This study applied the viscoelastic continuum damage mechanics (VECD) to investigate the fatigue behavior of asphalt mixtures. The fatigue life of typical asphalt mixtures was evaluated through four-point bending tests under various conditions. The strain-modulus empirical equation was firstly employed to fit the experimental data. However, it was noted that this equation was not entirely suitable for all conditions, as factors like temperature and loading frequency can influence fatigue life not only through the dynamic modulus but also via the damage properties of asphalt mixtures. To address this limitation and achieve a comprehensive fatigue life prediction equation, the Time-Strain Superstition Principle (TSSP) and Frequency-Strain Superstition Principle (FSSP) were introduced to characterize the impact of temperature and loading frequency on fatigue life, which can reduce fitting errors. Additionally, a mechanical prediction equation was also derived by the VECD approach, and its applicability under different conditions was explored. The results revealed that the damage characteristic curve (C-S curve) remained unaffected by loading frequency and strain level but was highly dependent on temperature. Significant fitting errors were observed in different temperatures when employing the VECD method for fatigue life prediction, as the VECD method did not account for the influence of temperature on the viscoelastic properties of asphalt mixtures, which in fact plays a critical role in fatigue life. In response, temperature adjustment coefficients were introduced into the derived equation. The predicted results demonstrated that the newly modified method significantly improved prediction precision, yielding an error of less than 20%.

Influence of Wetting-Drying cycles on the linear viscoelastic properties of asphalt mixtures

The top asphalt layers of pavement structures are subjected to loading demands and multiple environmental factors. Even though existing studies on moisture damage in asphalt mixtures have demonstrated the deleterious effects of water on different mechanical properties of these materials, the impact caused by changes in the partial saturation during the application of wetting–drying cycles on the linear viscoelastic properties of the mixture is an unexplored field. This study quantifies, for the first time, the changes in these properties (i.e., dynamic modulus, |E*|, and phase angle, ϕ) of a conventional asphalt mixture subjected to multiple wetting–drying moisture vapour cycles. The testing specimens were conditioned at five different relative humidity (RH) environments that were increased (wet path) or reduced (dry path) gradually, causing different saturation levels within their microstructures. The magnitude of |E*| and ϕ of the specimens was measured after reaching a steady state condition at each individual RH environment. In total, the specimens were subjected to five wetting–drying cycles and to a total of 41 dynamic modulus tests. The results corroborate that the degree of saturation impacts the linear viscoelastic properties of the mixture and show the irreversible effect of wetting–drying cycles on these properties. Since the dynamic modulus is an input parameter in the design of flexible pavements, the results also suggest that the degradation of this property due to changes in the partial saturation under field conditions could be included as part of existing mechanistic-empirical design methodologies.

Characterization and evaluation of coarse aggregate wearing morphology on mechanical properties of asphalt mixture

To evaluate the impact of coarse aggregate morphology on the mechanical performance of the asphalt mixture, the coarse aggregates with diverse wearing times were prepared and the corresponding asphalt mixture samples were compacted. The morphology characteristics of coarse aggregate under diverse wearing times were evaluated by an image measurement system. The dynamic modulus test and repeated loading creep tests were carried out to evaluate the viscoelastic properties and permanent deformation resistance of the asphalt mixture. The results indicated that the angularity index and three-dimensional sphericity could well characterize the wearing morphology. With the increase of wearing time, the angularity index of coarse aggregate gradually decreased, and the three-dimensional sphericity gradually increased. The balanced complex modulus Ge* and rheological parameter RG could effectively characterize the viscoelastic properties of asphalt mixture. As the angularity index increased, Ge* increased linearly, and RG decreased linearly. However, the Ge* and RG showed the opposite trend with the increase of three-dimensional sphericity. The flow number FN and the combination parameter εp/FN were the indexes to evaluate resistance to permanent deformation of the asphalt mixture. As the angularity index increased, the value of εp/FN decreased linearly, and FN increased linearly. With the increase of three-dimensional sphericity, εp/FN increases linearly and FN decreases linearly. The research results can provide a reference for the selection of coarse aggregate considering the morphological characteristics, and then improve the performance of asphalt mixture.

3D creep behaviour of asphalt mixtures: Experiment and modelling from complex modulus tests

The linear viscoelastic properties of asphalt mixtures can be characterised by the complex modulus or the creep compliance. This paper focused on the creep behaviour of asphalt mixtures and the relationship between the creep behaviour and the complex modulus of asphalt mixtures. 3D complex modulus tests, in which the complex modulus E* and complex Poisson’s ratio ν* were measured, were performed on three asphalt mixtures at six temperatures and five frequencies. The creep tests including loading at fixed constant stress of 0.5 MPa and recovery periods were carried out at three temperatures 15 °C, 30 °C and 60 °C. In addition to the axial strain, the radial strain was also measured in the creep test. The 2S2P1D model was used to simulate the E* and ν* of tested asphalt mixtures and then to calibrate the 3D generalized Kelvin–Voigt model. The evolution of axial and radial strain in the creep – recovery tests were modelled using the creep compliance function obtained from 3D generalized Kelvin–Voigt model. The results showed that the E* and ν* curves generated by 2S2P1D and GKV models fit well with the experimental ones. The transformation from 2S2P1D to generalized Kelvin–Voigt model respected the time–temperature superposition principle. The simulation of 3D creep tests can be established from generalized Kelvin–Voigt model and gives the similar results to experimental data for both loading and recovery period. The evolution of axial and radial strain in the creep – recovery tests respects the time–temperature superposition principle and can be modelled from the E* and ν* of tested asphalt mixtures.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature variations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the numerical analysis. Various temperature ranges (-20 to −10 °C, −10 to 0 °C), cyclic cooling rates (10 °C/h, 20 °C/h), low-temperature performance cooling rates (10 °C/h, 8 °C/h, 6 °C/h, 4 °C/h, 2 °C/h) and pre-crack dimensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.

Numerical and analytical length scale investigation on viscoelastic behavior of bituminous composites: Focusing on mortar scale

• Measuring LVE properties of bituminous composites through a multiscale simulation. • Multiscale simulation has more accuracy than the generalized self-consistent scheme. • 3.35 mm is the best mortar cutting size to find mixture behavior with NMAS of 19 mm. Viscoelastic properties of asphalt mixture were studied through a multi-scale approach, including bitumen, mastic, mortar, and mixture length scale. Biphasic and triphasic finite element modeling were employed to construct the heterogeneous models of bituminous composites, including matrix, inclusions, and air voids. The 2S2P1D model consisting of two springs, two parabolic creep elements, and one dashpot was fitted on the output of the numerical model, i.e., dynamic modulus (E*) and phase angle (δ), to accurately determine the Prony series. Then, the data of each scale was utilized as a matrix for the next scale’s model. Three cutting sizes, including 3.35, 2.36, and 1.7 mm were selected based on the previous experimental study of Khodadadi et al. (2021) to generate the mortar model and find the best length scale of the matrix. In addition, the numerical results were compared with the results of the generalized self-consistent scheme model as an analytical approach. Both numerical and the generalized self-consistent scheme models yield adequate results; nevertheless, the numerical solution has more accuracy than the analytical model. The cutting size of the mortar scale had a considerable effect on the LVE properties of the mixture. The result showed that a cutting size of 3.35 mm is more suitable for a mixture with a nominal maximum aggregate size of 19 mm. These findings were consistent with the experimental results.

Evaluating fatigue resistance based on viscoelastic properties of asphalt mixtures

ABSTRACT In this study, the fatigue resistance of different asphalt mixture types subjected to the same aging condition was evaluated using linear viscoelastic properties of asphalt mixtures. The relaxation spectra were determined from the dynamic modulus test based on the linear viscoelastic theory, and the relationship between the parameters of relaxation spectra and the parameters of the storage modulus master-curves were developed. The Texas overlay test was conducted to evaluate the fatigue resistance with the number of load cycle to failure used as the measure of fatigue resistance. From the corresponding results, it is shown that the inflection point frequency of the dynamic modulus master-curves could be used to assess the fatigue resistance compared to other parameters. The Glover-Rowe parameter also exhibited a fair relationship with the fatigue resistance of the asphalt mixtures. The effect of the shape parameter (γ) of the dynamic modulus master-curves was quantified but seemed not very sensitive to fatigue resistance for the asphalt mixtures evaluated. In the study, a new parameter (VECIndex) was developed to evaluate the fatigue resistance, which considered the inflection point frequency and shape of the dynamic modulus master-curves, both of which influence the linear viscoelastic properties and fatigue resistance of asphalt mixtures.

Experimental analysis and predictive modelling of linear viscoelastic response of asphalt mixture under dynamic shear loading

The use of predictive models can facilitate the inclusion of shear parameters in asphalt mixture evaluation and design processes. Unlike more extensively studied tension–compression models, the currently existing shear model, the Hirsch model, has unrealistic constants, particularly for the prediction of phase angle. Aiming at an improved predictive model in shear, this study employs a simple shear apparatus to experimentally analyse the linear viscoelastic properties of asphalt mixtures for road paving. Master curves were constructed and compared between different asphalt mixtures. Additionally, the test results were also analysed in the Black space and the Cole-Cole space. The dynamic shear response of asphalt mixtures was thereafter modelled on the basis of the Hirsch model. As the original model for phase angle prediction was found to be unrealistic, a particular focus in this study was put on identifying realistic empirical relationships for predicting the phase angle of asphalt mixtures in shear. More reliable shear test results of asphalt mixtures were used to calibrate the model, and extra test data were utilized to validate the calibrated model. It is indicated that the predictive model after calibration could deliver results of greatly improved accuracy, especially at the high-frequency and low-frequency ends. The analysis and modelling also leads to realistic empirical relationships for predicting the phase angle of asphalt mixtures in shear. The experimental verification confirms the good prediction accuracy of the calibrated model and proposed empirical relationships.

Linear viscoelastic response of semi-circular asphalt sample based on digital image correlation and XFEM

Asphalt mixtures behave as linear viscoelastic materials when subjected to loading conditions that are similar to pavement operating conditions. Thus, this study proposed a novel method for extracting the linear viscoelastic properties of asphalt mixture at 25 °C using digital image correlation and repeated-load semi-circular bending (SCB) test. Digital image correlation was utilised successfully for extracting creep compliance using semi-circular samples under repeated loading conditions. A fractional time-dependent viscoelastic element converted the creep compliance data into relaxation modulus. The extracted relaxation modulus data were verified by simulating the viscoelastic response of control and modified asphalt mixtures using the extended finite element model (XFEM). The findings presented in this paper showed that digital image correlation has a high potential for bridging the gap between experimental and simulation work. The strain map provided by the prediction model was compatible with the DIC strain.

Microstructure and Meso-Mechanical Properties of Asphalt Mixture Modified by Rubber Powder under a Multi-Scale Effect

The applications of rubber-modified asphalt and its mixtures have received widespread attention due to the environmental and economic benefits of such materials. However, studies on the structural performance of rubber-powder-modified asphalt pavement are only concentrated on a certain scale, leading to research on the structural performance of pavement mostly focusing on mechanical responses at a macro scale. Therefore, the present study adopts the concept of multi-scale research to analyze the viscoelasticity of high-dosage-modified asphalt and its mixtures at a microscopic scale from the perspective of meso-mechanical analysis. In this paper, to ensure the overall durability of a structure, the effective asphalt film thickness and coarse aggregate angularity index of the test material were measured first. The viscoelasticity of asphalt modified with rubber powder was then analyzed using a Brinell viscosity test, scanning electron microscopy (SEM), and a dynamic shear rheometer (DSR). We determined the optimal amount of rubber powder to be 30%. A universal testing machine was used to study the influence of different temperatures and loading frequencies on the viscoelastic properties of different asphalt mixtures. Research on the dynamic modulus found that the incorporation of rubber powder increases the elastic properties of the mixture such that the rubber-powder-modified asphalt mixture had a higher dynamic modulus. At the same time, the high-dosage-modified asphalt mixture was found to be closer to an elastomer under a low temperature and high frequency. At a high temperature and low frequency, the asphalt mixture changed into a viscoelastic body whose viscous properties were mainly affected by the asphalt binder. The addition of rubber powder changed the temperature sensitivity of the asphalt and then affected the viscoelastic properties of the asphalt mixture.

Effect of relative humidity on the linear viscoelastic properties of asphalt mixtures

It has been demonstrated that humidity, or water vapor, is a non-negligible contributor to moisture damage of asphalt pavements. However, little work has been done regarding the effect of humidity on the performance of asphalt mixtures. The objective of this paper was to investigate the linear viscoelastic (LVE) properties of asphalt mixtures under different humidity conditions. Specimens were first conditioned at four humidity levels and subsequently employed to perform dynamic modulus tests. Next, a shifting method for the master curve under humidity conditions was proposed to quantify the influence of water vapor on LVE properties of asphalt mixtures. Finally, the effect of humidity on LVE properties of asphalt mixtures was analyzed based on three aspects. The results show that the developed shift method is accurate enough to quantify the effect of humidity on master curves of asphalt mixtures since the error in any group is less than 2%, while each R2 value exceeds 0.98. The rheological parameter Ee decreases, and R and m increase as the humidity levels rise. However, no obvious variation trend was found in the Eg, k, and fc of different groups. The humidity factor g(Hi) shows a negative increasing trend based on the rise in humidity levels. Meanwhile, according to the developed three-dimensional master curves of dynamic modulus and phase angle of the two types of mixtures, dynamic modulus decreases and phase angle increases as humidity levels rise at low frequencies (or high temperatures). No significant differences were observed on dynamic modulus and phase angle among different groups at high frequencies. Thus, the developed three-dimensional dynamic modulus and phase angle master curves can determine dynamic modulus and phase angle under arbitrary humidity conditions.

Characterization of viscoelastic properties of asphalt mixture at low temperatures using DC(T) creep test

This study presents a framework to identify the low-temperature viscoelastic properties of asphalt concrete using the disk-shaped compacted tension (DC(T)) creep test. Due to the DC(T) geometry, the stress–strain state in the DC(T) geometry is not simple, and a geometry coefficient is needed to characterize the relationship between the mechanical and geometrical properties. The geometry coefficient of DC(T) was calculated by invoking the correspondence principle in viscoelasticity. The DC(T) creep test was conducted on different asphalt mixtures comprised of various components and modifiers at three temperature levels of 0, −12, and −24 °C. The creep compliance function for each of these mixtures was modeled using a generalized Voigt-Kelvin spring-dashpot phenomenological representation. The numerical implementation of the generalized Voigt-Kelvin model was developed in the finite element code Abaqus via a user material subroutine (UMAT). Numerical simulations of DC(T) creep tests using the identified viscoelastic properties are presented, which indicate the capability of the proposed approach to characterize the low-temperature linear viscoelastic behavior of the investigated asphalt mixtures. To further validate the viscoelastic properties obtained from DC(T) test through different stress–strain states, numerical simulation results from an Indirect Tensile Creep Test were compared to experimental results. The close agreement found between the results of indirect tension creep tests and numerical simulations indicates the capability of the proposed approach for identification of viscoelastic properties of asphalt mixtures at low temperatures, which opens the door to avoid the intricate experimental setup and poor repeatability of the indirect tensile creep test at low temperatures.

Effect of time–temperature, strain level and cyclic loading on the complex Poisson’s ratio of asphalt mixtures

Complex modulus and complex Poisson’s ratio are two parameters which characterise the 3D linear viscoelastic properties of asphalt mixtures. Compared to the complex modulus, the complex Poisson’s ratio is more difficult to be measured because of the great accuracy needed for the experimental device. This investigation focuses on the complex Poisson’s ratio of asphalt mixtures and the effect of loading parameters on its values. The three loading parameters considered in the paper include the time–temperature, the strain level and the number of cyclic loadings. To fulfil the objective of study, complex modulus tests, fatigue tests combined with the rest time, large amplitude cyclic loading tests and cyclic permanent deformation tests are performed. The complex modulus tests are conducted at different temperatures, frequencies and strain amplitudes. Thanks to the fatigue tests, the large amplitude cyclic loading tests and the cyclic permanent deformation tests, the change in complex Poisson’s ratio with the number of cycle, the pre-deformation strain level of specimen and the accumulated permanent deformation (up to some %) respectively is also investigated. The obtained results show that the time–temperature and the number of cyclic loading have a clear effect on the complex Poisson’s ratio of asphalt mixtures. No significant change in the complex Poisson’s ratio is observed when varying the strain cyclic loading amplitude within the small strain domain. The change in the complex Poisson’s ratio becomes more important and is observed to be proportional with the norm of the strain deviator tensor when the axial strain is accumulated or pre-loaded up to some percent.

Development of time-temperature-humidity superposition principle for asphalt mixtures

Variation of the humidity in asphalt layers may very likely induce change in the viscoelastic properties of asphalt mixtures. It has been the authors’ speculation that humidity is an important factor in the properties of asphalt mixtures, just like temperature. However, it has not been reported in the literature regarding how humidity influences the viscoelastic properties of asphalt mixtures.This study developed a time-temperature-humidity superposition principle for asphalt mixtures and established temperature-humidity correspondence. The magnitude of the complex modulus |E∗| and the phase angle of the complex modulus ϕ of typical asphalt mixtures were measured at a number of combinations of temperatures and humidity levels, and the humidity-dependency of the viscoelastic properties of asphalt mixtures was identified. The time-temperature-humidity shift factor was derived for the construction of master curves of |E∗| and ϕ at the reference state. The goodness of model fit validated the developed time-temperature-humidity superposition principle. The equivalent effect of humidity on |E∗| and ϕ was evaluated with respect to temperature.This study demonstrated the significant effect of humidity on the viscoelastic properties of asphalt mixtures. The developed time-temperature-humidity superposition principle is important in determining the time-dependent and humidity-dependent viscoelastic properties of asphalt mixtures from known properties at a reference temperature and a reference humidity.

Exploring creep and recovery behavior of hot mix asphalt field cores with multi-sequenced repeated load test

Rutting is known as a major distress in hot-mix asphalt (HMA) pavements. In order to fully characterize the creep and recovery behaviors of HMA mixes under varying loading conditions at high temperatures, a newly modified multi-sequenced repeated load test with a greatly improved sampling rate of 500 in a second was developed and performed on HMA field cores. Various indicators, including maximum strain, recovered strain, un-recovered strain, resilient modulus (Mr), non-recoverable creep compliance (Jnr), and percent recovery (R%) were proposed to investigate the visco-elastic properties of asphalt mixture. The stress-dependencies of these indicators were analyzed, besides, the correlation and ANOVA analyses were also conducted. Based on the analysis results, it is found that all analyzed indicators except Mr show significant stress-dependency; the vast majority of strain can be recovered (R > 99%), and an increased stress plays a negative role in recovery behavior. The facts indicate that only in a wider stress domain can the visco-elastic characteristics of HMA mixes be fully understood, furthermore, Jnr and R are superior to other indicators in statistically differentiating the viscous and elastic properties of different asphalt mixtures, respectively.

Viscoelasticity Evaluation of Regenerated Asphalt Containing Waste Engine Oil Based on Rheological Analysis

In order to explore the viscoelastic properties of waste engine oil (WEO) on mixed asphalt, mixed asphalt was prepared by fusing base asphalt and aged asphalt. The effect of waste engine oil content on the physical and viscoelastic properties of asphalt mixtures was studied through experiments. The test results show that the viscosity and softening point of asphalt mixture is reduced by adding waste engine oil. The complex modulus (G*) of asphalt binder decreases with the addition of waste oil at different test frequencies. With the increase of waste oil content, the phase angle (ä) of asphalt mixtures increases at specific frequencies. When the content of waste oil exceeds 6%, G* and δ will not change significantly. The stiffness increase caused by ageing asphalt in mixed asphalt will be offset by adding 2-4% waste oil. This indicates that waste oil can be used as regenerant to provide elasticity and flexibility for asphalt binder.

Study on Mechanical and Viscoelastic Properties of Asphalt Mixture Modified by Diatomite and Crumb Rubber Particles

To optimize the properties of asphalt mixtures and make full use of waste rubber tires, diatomite and crumb rubber particles were applied to reinforce the asphalt mixtures in this study. The rutting tests, the three-point bending tests, the freeze-thaw splitting tests, and the uniaxial compression creep tests were performed to analyze the effects of asphalt types and aggregate gradation on the pavement properties of diatomite and crumb rubber particles reinforced asphalt mixtures (DRPAM). Subsequently, the creep and relaxation characteristics of DRPAM were analyzed by the Burgers model, the modified Burgers model, the second-order extensive Maxwell model, and the Scott–Blair model. The results show that rubber particles and diatomite can reinforce the high temperature, low temperature, and viscoelastic properties of asphalt mixtures, although the improvement effect is weaker than styrene-butadiene-styrene (SBS). Consequently, it is concluded that rubber particle and diatomite compound modified asphalt mixture with suspension dense gradation and SBS binder will have better performance.