Viscoelastic Continuum Damage Model Research Articles

Nonlinear viscoelastic effect on the fatigue performance of wood tar-based rejuvenated asphalt

The nonlinear viscoelasticity (NLVE) effects of rejuvenated asphalt are often neglected during fatigue degradation, potentially leading to misjudgment of its true fatigue performance. To more accurately quantify the fatigue life of rejuvenated asphalt under NLVE effects, frequency sweep (FS), incremental stress sweep (ISS), and linear amplitude sweep (LAS) tests were used to study two types of rejuvenated asphalt. FS and ISS tests respectively obtained the dynamic modulus |G*|LVE and |G*|NLVE representing the linear viscoelasticity (LVE) and NLVE of rejuvenated asphalt, and incorporated them into the simplified viscoelastic continuum damage (S-VECD) model to establish the fatigue failure criterion and predict the fatigue life of rejuvenated asphalt under high strain levels in LAS tests. The findings indicate that the NLVE-based-S-VECD model quantifies fatigue damage in rejuvenated asphalt lower than the LVE model, and the fatigue life of rejuvenated asphalt increases significantly after considering the NLVE effect. Besides, the failure difference (∆GR) and failure area difference (∆A) defined during the modeling process explain the impact of NLVE on the fatigue failure criterion average pseudo strain energy release rate (GR) of rejuvenated asphalt, validating the necessity of incorporating NLVE into the fatigue performance analysis of rejuvenated asphalt. Therefore, it's necessary to account for the impact of NLVE effect on the fatigue performance of rejuvenated asphalt in engineering practice, which will contribute to the development and application of rejuvenator.

Effect of SARA Fractions on Fatigue Properties of Hard Asphalt.

The fatigue performance of hard asphalt is an important factor that affects the service life of asphalt pavement. In order to comprehensively explore the influence of chemical components on the fatigue performance of hard asphalt, and to eliminate the chemical instability between the microstructure of asphalt from different oil sources, seven kinds of hard asphalt were designed and prepared with saturates, aromatics, resins, and asphaltenes (SARA) extracted from the same hard asphalt. Rheological, time sweep and linear amplitude sweep (LAS) tests were carried out to evaluate the fatigue properties. The results show that the complex modulus of asphalt binds increased rapidly with an increase of asphaltene and resins and that the colloidal structure was strengthened, which would increase the fatigue factor. In the time sweep test, the strength of the colloidal structure significantly affected the fatigue life, and the fatigue life was different under different test stresses. In the viscoelastic continuum damage (VECD) model, the cumulative damage was related to the modulus, while with the increase of asphaltene and resins, the fatigue life showed a trend of first increasing and then decreasing. The linear regression analysis showed that the fatigue life of hard asphalt had a good correlation with strain sensitivity. This study investigated the applicability of different fatigue evaluation methods and revealed the influence of four components on the fatigue properties of hard asphalt. The results provide significant insights in the improvement of the fatigue performance of both hard asphalt and corresponding mixtures.

Quantitative study on fatigue characteristics of warm mix recycled asphalt

The warm mix recycling technology of asphalt pavement can improve the utilization rate of solid waste in highway construction industry on a large scale, and reduce the emission of harmful gases ( NOX, CO2, benzopyrene, etc.) in the process of road construction. It is one of the effective ways to realize carbon neutrality in highway construction industry. The main purpose of this study is to systematically analyze the fatigue characteristics of warm mix recycled asphalt (WMRA) from the perspective of quantitative research, and to provide scientific basis for the popularization and application of this technology. Therefore, this study mainly evaluated the anti-fatigue characteristics of WMRA under different conditions based on the linear amplitude sweeping test ( LAS test). Based on the calculation and analysis of the commonly used fatigue judgment indexes ( stress-strain curve, phase angle-strain curve, S×N curve ( S is the ratio of the instantaneous modulus to the initial modulus of the material, which is often replaced by the virtual modulus in the LAS test, and N is the number of cyclic loadings.), virtual strain storage energy-strain curve), the peak strain of virtual strain storage energy is recommended as the fatigue judgment standard from the perspective of reliability and accuracy, and the peak strain of damage factor is proposed as one of the new fatigue judgment standards. In this paper, the nucleation of microcracks and the coalescence of microcracks are distinguished in the process of fatigue damage evolution, and the peak strain of virtual strain energy storage and the peak strain of damage factor are used as the judging indexes respectively. Finally, based on the theory of continuum damage mechanics, the loss modulus of WMRA is selected as the representative value of material properties to calculate the virtual modulus and damage factor, and the fatigue damage evolution model of WMRA based on the viscoelastic continuum damage model ( VECD model) was constructed. Based on this model, the anti-fatigue characteristics of WMRA with the reclaimed asphalt pavement ( RAP) content were analyzed.

Effects of non-linearity and thixotropy in linear amplitude sweep testing for the evaluation of self-healing of bituminous binders

Linear amplitude sweep tests have been demonstrated to have good potential in being used for the evaluation of self-healing properties of neat and polymer-modified bituminous binders. Past research works, however, have neglected the effects of material non-linearity and thixotropy. This implies that the whole material integrity loss is attributed to damage and all restoration to self-healing, thus resulting in the possible overestimate of both damage and self-healing when evaluating the fatigue performance of materials. In the study described in this paper, specific experimental and analytical methods were adopted with the purpose of separating non-linearity and thixotropy in LAS healing tests. Non-linearity was assessed by means of multiple strain sweep tests carried out to determine the material non-linear viscoelastic moduli at specific testing temperatures. Thixotropy was considered by coupling self-healing LAS testing with a purposely defined test in which loading was applied to the undamaged material after a rest period equal to that applied in self-healing tests. Obtained results were processed by means of an analytical approach based on the simplified viscoelastic continuum damage model. Quantification of self-healing included the determination of material integrity and damage parameters recovered after the rest period. Such parameters, calculated by excluding time-dependent and non-linear biasing effects, can be used as straightforward indicators of the self-healing potential of neat and polymer-modified bituminous binders. Moreover, obtained results substantiate the concept that time–temperature superposition is still applicable when non-linearity is incorporated into the simplified viscoelastic continuum damage model.

Evaluating the Fatigue-Cracking Resistance of North Dakota’s Asphalt Mixtures

Fatigue cracking is a critical pavement distress caused by extreme environmental conditions and heavy repeated cyclic loading. Performance-based design methods that use mechanistic models focus on material performance properties, creating an opportunity to use engineered and recycled materials such as reclaimed asphalt pavement (RAP). The primary goal of this study was to use the simplified viscoelastic continuum damage (S-VECD) model to assess the fatigue behavior of North Dakota’s asphalt mixtures. Eight mixtures typically used in North Dakota were sampled and underwent | E*| testing to determine their linear viscoelastic (LVE) properties. The S-VECD tests were conducted on the same mixtures to determine their damage characteristics. The outputs from the two tests were exported to the FlexMATTM software to obtain their damage characteristic curves, DR failure criterion parameters, and Sapp-index values. CT-index values for the same mixtures were obtained from the North Dakota Department of Transportation (NDDOT). The results revealed that the mixture used for HWY 52, which does not contain RAP, was least susceptible to fatigue cracking. The mixture used for HWY 6, which contains the highest RAP content (25%), had the lowest fatigue resistance, revealing RAP’s stiffening effect on asphalt mixtures. The mixture used for HWY 1, which used the performance grade (PG) 58S-34 binder, had the second-highest fatigue-cracking resistance despite containing 15% RAP, indicating that binder grade affects an asphalt mixture’s fatigue behavior. A relatively low correlation was observed between the CT-index and Sapp-index.

Modeling damage caused by combined thermal and traffic loading using viscoelastic continuum damage theory

Various engineering models have been proposed to mitigate fatigue cracking associated with thermal and traffic loadings, which are the two primary fatigue cracking mechanisms that negatively affect the service life of asphalt pavement. Thermal fatigue cracking is induced by cycles of temperature changes with relatively long time periods, which can be regarded as slow frequency sinusoidal loading. Traffic fatigue cracking is induced by numerous vehicle load repetitions and is often characterized using fast frequency sinusoidal loading. These two loading types occur simultaneously in the field. In order to investigate how to properly model the damage due to these two loading types, a set of tests that vary the load, frequency, and mode of testing was designed to mimic the scenarios that asphalt pavements experience under thermal loading and traffic loading separately and under the combined and simultaneous effects of both thermal and traffic loading. The viscoelastic continuum damage (VECD) model was applied to simulate the changes in material integrity under each condition. After determining the appropriate configuration for the proposed prediction model, the material integrity predictions were found to be accurate for the fast frequency tests but less accurate for the slow frequency tests. This difference is attributable to plasticity being a much more significant factor under slow frequency conditions than under fast frequency conditions. For the tests combining both fast and slow frequency conditions, the material integrity results oscillated continuously. It was postulated that these oscillations were due to the recovery mechanisms of asphalt concrete such as nonlinearity and healing. When the simplified viscoelastic continuum damage (S-VECD) model was applied, which does not consider the material’s recovery characteristics, the predicted material integrity was able to match the overall trend observed in the tests. Ultimately, a new way to model combined damage simultaneously under two cracking mechanisms (thermal fatigue cracking and traffic fatigue cracking) is introduced in this paper.

Development of a Framework for Assessing Bitumen Fatigue Cracking Performance under Different Temperatures and Aging Conditions

A full understanding of bitumen fatigue cracking behavior is extremely important as this phenomenon has a considerable influence on bituminous pavement performance. The current framework for assessing this asphalt binder property is inconsistent in ranking bitumen fatigue performance in terms of the failure definition and damage characteristic curve (DCC) analysis. This study used four different types of asphalt binders: neat asphalt (NA), self-healing thermoplastic polyurethane (STP)-modified bitumen, self-healing poly (dimethyl siloxane) crosslinked with urea bond (IPA1w)-modified bitumen, and styrene–butadiene–styrene (SBS)-modified bitumen (SBSB). All the bitumens were subjected to short-term and long-term aging, and they were also tested by utilizing the linear amplitude sweep (LAS) test and the simplified viscoelastic continuum damage (S-VECD) model. LAS and S-VECD procedures were used to apply the newly proposed and current frameworks in order to analyze bitumen performance. The current framework showed that the bitumens that used a higher number of loading cycles (N) to reach their failure points (Nf) failed to exhibit greater fatigue performances in terms of DCC analysis. The developed framework (mainly based on the damage intensity [S] instead of N) was used to solve the inconsistency between the failure definition and DCC assessment in ranking bitumen performance. Additionally, the current framework (failure criterion) presented two R2 values below 0.1, but the developed framework (failure criterion) showed that all R2 values were greater than 0.9. The developed framework represents a turning point because, for the first time, this type of procedure is mainly being based on S instead of N. Although further tests are needed to confirm its efficiency, it eliminates the inconsistency between the failure definition and DCC assessment.

Influence of Modified Stalk Fibers on the Fatigue Performance of Asphalt Binder

The type and content of modified stalk fibers significantly influence the fatigue properties of asphalt binder. In this study, different concentrations of NaOH solution were used to modify stalk fibers, and scanning electron microscopy (SEM) was used to observe the effect of the modified concentration on the fiber morphology. A dynamic shear rheology (DSR) test and a linear amplitude sweep (LAS) test were conducted to analyze the effects of the fiber type and content on various factors such as the complex shear modulus G*, phase angle δ, and fatigue parameters (A35 and B). Consequently, the fatigue life Nf of the fiber asphalt binder was calculated using a viscoelastic continuum damage model. The results show that stalk fibers modified using a 5% alkali solution exhibited the best oil absorption and heat resistance, the asphalt binder with a 1.5%–2% fiber content exhibited the best resistance to fatigue, and the fatigue performance of the asphalt binder with different types of fibers was superior when fiber doping was at 1.5%. Additionally, the fatigue parameter A35 of the modified cotton and corn stover fibers increased by 40.5% and 57.6%, respectively, and the fatigue parameter B decreased by 5.8% and 4.8%, respectively, compared with that of the unmodified stover fibers. Finally, the modified corn stalk fiber asphalt binder with a 1.5% fiber content demonstrated the best fatigue resistance.

System Identification Framework for Modeling of Static Creep and Dynamic Creep Behavior of Dense-Graded Asphalt Mixtures

The response of two dense-graded asphalt concrete (AC) mixtures under static and dynamic creep tests conducted in compression is modeled using the principles of the system identification framework in this study. The AC materials under static and dynamic creep loading conditions exhibit complex behavior patterns such as history dependency, plasticity, and temperature dependency. It is desired to formulate a constitutive model describing these complex phenomena. The empirical approach is outside the scope of this study. A viscoelastic continuum damage model requires individual experimentation to characterize linear and damage behavior. A viscoplastic model requires incremental deviator stress for plastic deformation. Both static and dynamic creep tests do not satisfy this condition. Therefore, the “system identification” approach is used in this study. Two methods of system identification approach—that is, black box and grey box modeling—are adopted to characterize static and dynamic creep behavior of AC. Of these two models under consideration, the black box models were versatile in modeling complex loading situations with a high degree of accuracy but lacked physical interpretation. While the grey box models have a physical interpretation, they are not as versatile as black box models.

Quantitative analysis of oxidative aging effects on the fatigue resistance of asphalt mixtures based on the simplified viscoelastic continuum damage (S-VECD) model

Fatigue cracking evolution in asphalt pavement is coupled by the oxidative aging of asphalt binder throughout its lifespan. Identifying the quantitative effects of asphalt binder aging on the fatigue resistance of asphalt mixture is important for the long-life design of asphalt pavements. In this study, two fatigue indexes (DR and Sapp) derived from the simplified viscoelastic continuum damage (S-VECD) model, were used to evaluate the fatigue resistance of laboratory-aged asphalt mixtures. Asphalt binders were extracted from aged asphalt mixtures and tested by using Fourier transform infrared spectroscopy (FTIR) to assess their aging state based on two aging indexes, the carbonyl index and the sulfoxide index. It was found that the aging indexes and fatigue indexes are well related through two power functions. Hence, the relationship between aging evolution and fatigue modelling of asphalt mixtures can be well quantified. It is anticipated that these aging-fatigue functions can assist in modelling and predicting the fatigue resistance for asphalt pavements in the field.

Effect of Long-Term Aging on Fatigue and Thermal Cracking Performance of Polyphosphoric Acid and Styrene-Butadiene-Styrene-Modified Bio-Blend Bitumen.

Polyphosphoric acid (PPA) and styrene-butadiene-styrene (SBS) were adopted to produce PPA-SBS-modified bio-blend bitumen, which achieved excellent mechanical performance. However, its long-range performance, such as the fatigue and thermal cracking behavior under long-term thermal oxidation, is not well understood. Therefore, a pressure aging vessel (PAV) system was applied to simulate the aging behavior of the bitumen under the action of thermal oxidation. Then, a linear amplitude sweep (LAS) test combined with a viscoelastic continuum damage (VECD) model was applied to investigate the fatigue properties of the bitumen. Moreover, a bending beam rheometer (BBR) test was conducted to evaluate the thermal cracking resistance of the bitumen before and after PAV aging. Meanwhile, an atomic force microscope (AFM) was applied to observe the microscopic topography. The results show that the original compound-modified bitumen can bear more fatigue damage than that of the control bitumen at the failure point, and it also has excellent fatigue resistance at 2.5%, 5%, 7.5%, and 10% applied strain. Moreover, the VECD model can accurately predict the fatigue life of the bitumen under different applied strains. The variation ratio of stiffness modulus for the compound-modified bitumen is below that of the control bitumen after PAV aging, so it shows a better anti-aging performance. Finally, the AFM test shows that PPA and bio-bitumen decrease the heterogeneity of the bitumen, reducing the difference between phases.

Investigation of changing SARA and fatigue properties of asphalt bitumen under ageing and analysis of their relation based upon the BP neural network

Thermal oxidation has a significant effect on asphalt binders’ saturates, aromatics, resins, asphaltenes (SARA) fractions and fatigue properties, but its effect on the SARA of different asphalt binders and the relation between SARA and the fatigue performance is not clear. In this study, thin layer chromatography/flame ionization detection (TLC/FID) was applied to analyze the SARA of the 36 specimens of original, short-term aged, and long-term aged asphalt binders. And then the viscoelastic continuum damage (VECD) model was applied to analyze these asphalt binders’ fatigue. Finally, the relation between SARA and the binders’ fatigue was determined by back-propagation (BP) neural network. The results showed that asphalt ageing can be considered to be the conversion of the light constituents to heavy constituents but the conversion ratios differed significantly for different asphalt binders. Asphalt binders of the same grade but different origins may have completely different mechanical properties and exhibit an entirely different composition conversion during ageing. Saturates can be considered the most inert constituent in asphalt. The oil source is the critical factor that determines the SARA and its degree of change during ageing. Ageing increased all of the asphalt binders’ fatigue life under a low strain level, but decreased it under high strain. The fatigue performance of asphalt binders with the same oil origin and grade but different manufacturers, did not differ significantly, either in the original or the aged states. Further, training the BP neural network showed that asphaltenes had the most significant effect on the asphalt’s fatigue behavior, followed by the resins and saturates, while aromatics had a minimal effect. And the BP neural network can forecast asphalt binders’ fatigue performance accurately based upon the SARA.

A proposed approach for accurate fatigue quantification of the base asphalt binders coupling nonlinear viscoelastic effects in S-VECD theoretical framework

The nonlinear viscoelasticity (NLVE) effects at high loading amplitudes are neglected in the stiffness evolution and fatigue quantification for asphalt binders. This study is to determine the applicability of the simplified viscoelastic continuum damage (S-VECD) model considering NLVE effects to the fatigue test protocols of asphalt binders at high strain levels, and to identify the real damage degradation and fatigue life quantification. An equivalent non-linear complex modulus (|G*|NLVE) of the NLVE-based S-VECD model was proposed and quantified by incremental stress sweep testing. A refined fatigue failure criterion GRNL was proposed in the NLVE model. The effectiveness of NLVE on the released pseudo-strain energy (PSE) and failure criteria was also verified. |G*|NLVE values in NLVE region are lower than |G*|LVE values in LVE region. The linear viscoelasticity (LVE)-based S-VECD model overestimates the damage effectiveness on the stiffness degradation. A significant difference exists between the NLVE and LVE models in the damage characteristic curves of the asphalt binders. The actual damage quantified by the NLVE model is lower than that of the LVE model. For both types of binder, the GRNL parameter remains well linear with the fatigue life (Nf). The linear relationship between the released PSE shrinkage values (ΔΣWrR) and the reduced damage (ΔS) is clear when comparing the LVE and NLVE models. The NLVE model predicted a higher fatigue life for asphalt binders than that predicted by the LVE model. The fatigue life determined by the NLVE model exhibits a linear functionality to that quantified by the LVE model, which further validates the applicability and validity of the NLVE model for the diagnosis of fatigue measurement. In contrast, the NLVE-based S-VECD model predicts the fatigue life of asphalt binders under practical service conditions more closely to the mechanical response under actual traffic loads.

Asphalt mixture fatigue damage and failure predictions using the simplified viscoelastic continuum damage (S-VECD) model

Fatigue cracking is a primary asphalt pavement distress and various models have been developed to predict the fatigue life of asphalt mixtures using laboratory tests. One such model is the simplified viscoelastic continuum damage (S-VECD) model, which has been implemented in the pavement performance prediction program, FlexPAVETM. The S-VECD model test protocols (AASHTO TP 133 and AASHTO T 400) and data processing tool (FlexMATTM) are widely used around the world. Over the past three decades, this model has been continuously improved and refined. However, questions remain on the model’s ability to predict the material response when stress or strain are used as the model input. Also, different fitting procedures for the model calibration were found to affect the model’s prediction accuracy. In this study, analysis was conducted using data for four typical North Carolina mixes based on single replicate tests and multiple replicate tests to compare the model’s prediction accuracy based on stress versus strain as the model input and by considering fitting errors in the different calculations. The results show that using strain as the model input, which automatically incorporates portions of permanent strain, yields more accurate predictions compared to using stress as the input, regardless of the fitting algorithm. Additionally, in the analysis of individual test data, which is not affected by replicate specimen variability, the model’s predictions match the measured data well, as long as the fitting errors of the damage characteristic curve are controlled. When the data from replicate tests are analyzed together, although specimen variability compromises the S-VECD model’s prediction accuracy, failure can still be reasonably determined when strain is used as the model input.

A Comprehensive Analysis of Fatigue and Healing Capacity of Sasobit Polymer-Modified Asphalt from Two Perspectives: Binder and FAM

Wax-based Sasobit synthetic hard wax can be designed for producing asphalt with less energy consumption and lower carbon emissions in the pavement industry. This study investigated the effectiveness of Sasobit synthetic hard wax on microscopic properties, fatigue-fracture behavior, and healing potential of polymer-modified asphalt (PMA) from two perspectives: asphalt binder and fine aggregate matrix (FAM). First, microscopic morphology, dispersion mechanism, and thermal stability of styrene-butadiene-styrene (SBS)– and crumb rubber (CR)–modified asphalt binders under the influence of Sasobit synthetic hard wax were characterized. Second, linear viscoelastic properties and evolution law of fatigue life of Sasobit synthetic hard wax/polymer-modified asphalt binders and FAM with and without healing interval were assessed under the framework of the simplified viscoelastic continuum damage (S-VECD) model. Third, the correlation between properties of the modified asphalt binder and FAM was statistically analyzed by radar chart. Thermodynamic analysis indicated that Sasobit synthetic hard wax enhanced the thermal stability of PMA but slightly reduced the low-temperature performance. Morphological observations showed that Sasobit synthetic hard wax had limited effectiveness on the dispersion of the polymer particles in PMA. Dynamic modulus master curves and fatigue and healing tests demonstrated that Sasobit synthetic hard wax contributes to the stiffness, fatigue resistance, and self-healing capability of the asphalt binder and mixture. Finally, statistical analysis revealed that the asphalt binder performance lacked a close correlation with the FAM owing to the complex composition system.

Reliability analysis of damage prediction in asphalt pavement sections using FlexPAVETM program and S-VECD fatigue model

ABSTRACT With mechanistic and mechanistic-empirical modelling of pavement performance there are a considerable number of uncertainties that are inherent in the prediction process. Many of these sources of uncertainty are challenging to quantify, but one that is technically possible to evaluate is the effect of uncertainty in the characterisation and modelling of the mechanical properties of the asphalt concrete. In this study, the Bayesian inference-based Markov Chain Monte Carlo (MCMC) was used to estimate how uncertainties from the simplified viscoelastic continuum damage (S-VECD) model parameters propagate to pavement performance simulation errors in the FlexPAVETM program. Performance predictions were evaluated based on the propagation of three different material parameter uncertainties; (1) modulus, (2) damage characteristic curves, and (3) failure criterion. These factors were systematically varied according to chosen reliability levels and using data from real-world experimental data on different asphalt mixtures. High-performance computing resources were then used to predict pavement performance on the thousands of different combinations of material property uncertainty, and a simplified prediction algorithm was developed to more easily estimate the uncertainty. The results show that the simplified uncertainty prediction model could estimate the reliability of the damage and cracking predictions from FlexPAVETM within 1.2% and 4.8%, respectively.

Aging effect of damp-heat and saline-alkali environment on fatigue performance and chemical evolution of asphalt

ABSTRACT Asphalt in damp-heat and saline-alkali areas is prone to damage, which resulting in fatigue failure of the mixture. However, the aging damage of asphalt in these areas has not been paid enough attention, and there is a lack of effective evaluation method for asphalt’s fatigue performance. In this paper, the base asphalt and SBS-modified asphalt were immersed in several solutions (water, NaCl and Na2CO3) to simulate aging conditions and the frequency sweep test was employed to determine the viscoelasticity properties of the asphalt. And the fatigue properties of the asphalt were analysed by the simplified viscoelastic continuum damage model. The microstructural and chemical evolution of asphalt was investigated by SEM, FTIR, the pH value and total organic carbon tests. After being immersed, the anti-deformation properties of two asphalts were strengthened. The solution erosion led to an increased loss rate of the integrity factor C*, and resulting in weakened fatigue properties of asphalt. The oxygen-containing functional group gradually increased with the extension of immersion. There were chemical interactions in addition to physical interface disruption during the immersion process. Moreover, the influence of Na2CO3 solution on asphalt ranked first due to the highest molar concentration of Na+ and the OH− produced by hydrolysis of C O 3 2 − .

Effect of Different Anti-Stripping Agents on the Rheological Properties of Asphalt

Water damage is one of the main forms of early damage of highway asphalt pavement, which seriously affects the service performance of asphalt pavement. To address the problem of early water damage of asphalt pavement, the addition of anti-stripping agents in asphalt is an effective technical means. To further analyze the influence of anti-stripping agents on asphalt performance, Qingchuan rock asphalt, acylamine anti-stripping agent, fatty amine anti-stripping agent, rock asphalt + acylamine anti-stripping agent and rock asphalt + fatty amine anti-stripping agent were selected to modify the base asphalt. The rheological properties of modified asphalt were tested using a dynamic shear rheometer and bending beam rheometer. Combined with the mathematical-model-fitting test results of Sigmoidal, Burgers, viscoelastic continuum damage model (VECD), etc., the effects of different anti-stripping agents on the rheological properties of asphalt were evaluated through model parameters. The results showed that the Qingchuan rock asphalt could improve the high-temperature resistance to deformation of asphalt and improved the resistance to deformation of asphalt in a wide frequency domain but increased the risk of low-temperature cracking of asphalt. Acylamine anti-stripping agents and aliphatic amine anti-stripping agents reduced the elastic recovery ability and deformation resistance under a wide frequency domain of asphalt at high temperatures but enhanced the flexible deformation and ductility of asphalt at low temperatures. The compound anti-stripping agent not only improved the high-temperature deformation resistance of asphalt, but also improved the deficiency of rock asphalt’s low-temperature performance and effectively enhanced its performance.

A more accurate fatigue characterization of GO-modified asphalt binder considering non-linear viscoelastic behaviour and UV exposure effects

The non-linear viscoelastic (NLVE) behaviour at high load levels is often neglected when characterizing the fatigue performance of asphalt materials, leading to a conservative or even underestimated assessment of the fatigue durability. The incremental stress sweep tests were conducted to define the threshold load amplitudes of the graphene oxide-modified asphalt binders (GO-MA) in the NLVE domain. The linear and non-linear dynamic shear modulus (|G*|LVE and |G*|NLVE) at fatigue test conditions were separately incorporated into the simplified viscoelastic continuum damage (S-VECD) model to rigorously quantify the fatigue life of asphalt binders. The damage evolution and the corresponding fatigue life of GO-MA binders in LVE-based and NLVE-based S-VECD models were analyzed comparatively. The outcomes manifested that GO nanoparticles could enhance the fatigue life of the asphalt binder. The comparison outcomes demonstrate an increase in fatigue life prediction for the base binder and GO-MA when both NLVE behavior and aging effects are taken into account.

Application of the Viscoelastic Continuum Damage Theory to Study the Fatigue Performance of Asphalt Mixtures—A Literature Review

A viscoelastic continuum damage (VECD) model, which accounts for the effects of rate-dependent damage growth, has been successfully applied to quantify the reduction in the material integrity as a function of damage accumulation (characteristic curve) of asphalt mixtures. This paper presents an overview of the fundamentals of the VECD model and its simplifications (S-VECD) applied to the damage characterization of asphalt mixtures. It also presents a laboratory study carried out to evaluate the effects of the addition of reclaimed asphalt pavements (RAP) and a new binder (PG 64-22 or PG 58-16) on the fatigue performance of fine aggregate matrices (FAMs), in which the S-VECD theory was applied to analyze the results. The addition of RAP increased the stiffness and reduced the relaxation rate, resulting in FAMs that were stiffer and more susceptible to damage at high strain levels. The FAMs’ fatigue factors (FFFAM) indicated that the increase in RAP from 20% to 40% decreased the fatigue life of the mixtures. A strict control of the mixture variables is required, since the intrinsic heterogeneity of asphalt mixtures can lead to different characteristic curves for the same material.