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Currently, the research on the mechanical properties of rubber-modified asphalt mixtures primarily focuses on small-scale investigations, with insufficient exploration into the performance of rubber particles and their relationship with the mechanism and properties of modified asphalt mixtures. Limited studies have been conducted on large-scale rubber modification in asphalt mixtures. Due to frequent use and subsequent high damage to existing asphalt pavements, incorporating rubber-modified asphalt mixtures can partially alleviate premature deterioration. Dynamic modulus tests were conducted using MTS equipment under unconfined conditions to investigate the viscoelastic behavior of rubber-modified asphalt mixtures with high rubber content and elucidate the influence of rubber particle content on the elastic deformation and recovery capability. The dynamic mechanical properties of the mixtures were determined at different loading rates, temperatures, and types of rubber-modified asphalt mixtures. Based on the test data, variations in the dynamic modulus, phase angle, storage modulus, loss modulus, loss factor, and rut factor of the rubber-modified asphalt mixtures under different loading frequencies, temperatures, and types were analyzed. The results demonstrate the pronounced viscoelastic behavior of rubber-modified asphalt mixtures. The mixtures exhibit enhanced elasticity at low temperatures and high frequencies, while their viscosity becomes more prominent at high temperatures and low frequencies. Under constant test temperatures, an increase in load loading frequency leads to a higher dynamic modulus; conversely, a decrease in dynamic modulus is observed with increasing test temperatures. The dynamic modulus of ARHM-25 at a frequency of 10 Hz is found to be 12.99 times higher at 15 °C compared to that at 60 °C, while at 30 °C, the dynamic modulus at 25 Hz is observed to be 2.72 times greater than that at 0.1 Hz. Furthermore, the rutting resistance factors of the asphalt mixtures increase with loading frequency but decrease with temperature. The rutting factor for ARHM-13 at a frequency of 10 Hz is found to be 22.98 times higher at 15 °C compared to that at 60 °C, while at a temperature of 30 °C, the rutting factor for this material is observed to be 3.09 times greater at a frequency of 25 Hz than at 0.1 Hz. These findings suggest that rutting is most likely when vehicles drive at low speeds in hot weather conditions. [ABSTRACT FROM AUTHOR]

Fatigue damage can develop within asphalt pavement due to the continuous impact of driving loads and natural elements. Understanding the process of asphalt mixtures' fatigue damage is crucial for guiding the design, maintenance, and repair of asphalt pavement. This research aims to establish a model that characterizes the mixtures' modulus decay under a three-dimensional (3-D) stress state. Firstly, asphalt mixes were subjected to direct tensile (DT), indirect tensile (IDT), unconfined compressive (UC) strength and fatigue tests, and the resulting data were analyzed. Then, modulus decay models under DT, IDT, and UC conditions were established, and the modulus decay patterns under the three loading modes were compared and analyzed. Finally, using the fatigue stress strength ratio Δ (a fatigue resistance index for asphalt mixtures that takes into account the impacts of stress state and loading rate), a unified characterization model for asphalt mixes' modulus decay under a 3-D stress state was created. According to the study's findings, asphalt mixes' modulus decay during fatigue damage exhibits obvious nonlinear characteristics. While the asphalt mixes' modulus decay law with various loading modalities is similar under the same conditions, the decay rate may differ. Essentially, the speed of the modulus decay of a certain asphalt mixture primarily depends on the value of Δ during service. A larger Δ indicates a faster modulus decay. This study offers a theoretical foundation for the conversion from material fatigue damage to structural fatigue damage, which is vital for enhancing the asphalt pavements' construction quality and longevity. [ABSTRACT FROM AUTHOR]

Fatigue performance of asphalt mixture has been tested through different types of loading modes, including the uniaxial tension (UT), uniaxial compression (UC), and indirect tension (IDT) modes. However, fatigue test results from different modes are found to be dissimilar. This research aimed to develop a unique fatigue law suitable for different loading modes, using the Miller yield criterion. First, the strength and fatigue behaviors of asphalt mixture under UT, UC, and IDT modes were compared and discussed. Then, the strength yield surfaces and stress paths were obtained by the Miller yield criterion. Finally, a new stress ratio indicator was proposed to generate a unified fatigue law of asphalt mixtures that are suitable for different loading modes. The findings in this research are expected to provide references for deriving the fundamental fatigue damage law for the asphalt mixture based on the strength yield criterion. Highlights: The properties of strength and fatigue under different test methods were revealed.The strength yield surface stress paths were obtained by the Miller criterion.A new stress ratio (Ω) based on the Miller criterion was proposed.A unified fatigue law of the asphalt mixture under different loading modes was revealed. [ABSTRACT FROM AUTHOR]

Material resistance and performance are determined by the failure criterion for an asphalt mixture, affecting the scientific design of pavement. Conventional tensile, compression, bending, and split tests for asphalt mixture cannot fully reflect the complex stress and strain state of the pavement structure. In this paper, double confining pressure triaxial tests were performed on asphalt mixtures to generate three-dimensional complex stress states. In octahedral stress space, a failure criterion was established featuring the tensile and compressive meridians as well as the failure envelope curve. According to the generalized Hooke's law (GHL), a transformed three-dimensional strain failure criterion model (FCM) was established and its accuracy was validated by the axial strain. The correlation function between stress and strain FCMs was proposed. According to the elastic layered system theory and the principle that the load response is less than the structural resistance, a three-dimensional load check was performed on a typical asphalt pavement structure. The results show that top-down cracks tend to appear in the inner edge of the load at the top of the upper surface layer. This research provides theoretical support for the study of the characteristics of asphalt mixture strength and pavement design under complex stress conditions. [ABSTRACT FROM AUTHOR]

The fatigue resistance of an asphalt mixture is crucial to the pavement's durability and serviceability of pavement. The pavement structure is in a three-dimensional (3D) stress state. However, the conventional fatigue-resistance design index mostly considers a one-dimensional stress state, which is different from the field conditions. In this paper, the unconfined compression test (UCT), direct tension test (DTT), and splitting test (SPT) were selected to conduct the strength and fatigue tests. Based on the Ayyagari Vural yield criterion, the strength damage surface under various loading rates was established. Furthermore, a normalized fatigue equation was developed in a 3D stress state by determining the fatigue-damaged path based on the yield criterion. Finally, the fatigue-resistance models for the structural design were proposed by combining the strength models (including the octahedral shear stress model and the Ayyagari Vural model) and the normalized fatigue equation. The results indicate that the strength damage surface model is in an elliptic form, and the surface is abducent as the loading rates increase, and the Ayyagari Vural yield criterion can describe the fatigue failure process. Both fatigue-resistance design methods for pavement resistance take the interaction among three principal stresses into consideration and comply with the failure characteristics of actual pavement structures; the equivalent stress as a design index is more feasible in its actual application. This study could provide a reference for the fatigue-resistance design of asphalt mixture layers in a complex stress state and improve the reliability in the pavement structure. [ABSTRACT FROM AUTHOR]

An asphalt mixture is always in a complex stress state during the service life of pavement. Its resistance can be objectively characterized only by applying the strength theory to establish the failure criterion model in a three-dimensional stress state. Therefore, based on the double confining pressure triaxial test method, the failure characteristic test in complex stress state was carried out on AC-13 and AC-20 asphalt mixtures widely used in asphalt pavement in China. Meanwhile, according to the generalized octahedral theory, the experimental data of the failure characteristic point, and the strength characteristics of the asphalt mixture itself, the applicability of classical failure criteria, including Bresler-Pister, Ottosen, Willam-Warnke, Kotsovos, Podgorski, amended Zhao-Song, and twin-shear failure criteria was analyzed. In the aforementioned failure criteria models, the amended Zhao-Song failure criterion considered the difference in tension and compression of materials, the effect of hydrostatic stress, and the correlation of stress states of strength, which was consistent with the test results. Therefore, this model can be used as the resistance calculation model of asphalt mixtures in a complex stress state. [ABSTRACT FROM AUTHOR]

Highlights • The strength and fatigue tests of asphalt mixtures were implemented. • The evolution patterns of strength with loading rate were revealed. • The unified fatigue model of asphalt mixtures was established. • The behavior of thermal fatigue and strength failure was integrated. Abstract In order to reveal the thermal fatigue behavior of asphalt mixtures under low temperature conditions, the four-point bending beam tests of strength and fatigue were carried out. The asphalt mixtures are typical viscoelastic materials whose fatigue properties are significantly influenced by low loading frequency. Thus, the fatigue tests under low loading frequency were used to simulate the thermal fatigue of asphalt mixtures. Based on the nominal stress ratio (not considering the effect of loading rate on the strength value) and the real stress ratio (the strength value corresponding to the loading rate of fatigue test), the fatigue equations of asphalt mixtures under low temperature and low frequency conditions were established. The flexural strengths of the four-point bending beam tests at different loading rates at 0 °C, −10 °C and −20 °C were studied. The results show that the flexural strength of asphalt mixtures expresses a power function on the pattern of variation with the loading rates. The intersection of fatigue curve characterized by the nominal stress ratio and the abscissa axis is much larger than 1. The fatigue curve based on the nominal stress ratio cannot be extended to fatigue failure point (1,1). But the fatigue curve characterized by the real stress ratio can be extended to the strength failure point, whose fatigue life is 1. So, the behavior of strength failure and fatigue failure was integrated. The uniform characterization model of fatigue equations for asphalt mixture under low temperature and low loading frequency conditions was realized, which means that the fatigue equations and curves under different loading frequencies could be characterized by one equation and one curve. The results can provide a theoretical basis for predicting the thermal fatigue performance of asphalt mixtures under low temperature conditions more accurately. [ABSTRACT FROM AUTHOR]

The fatigue test methods under different test conditions have strong impact on the test results, which obstructs a precise evaluation of fatigue characteristic for asphalt mixtures. Different test conditions means different stress states. Fatigue characteristic of a material is an objective attribute, and it should not vary with test methods and conditions. In order to accurately and objectively evaluate the fatigue properties of asphalt mixtures, a normalization model of fatigue characteristics for asphalt mixtures under different stress states was established based on the yield criterion in 3 dimensional stress states and the patterns of variation between the strength and the loading rate. The compressive, tensile and indirect tensile strength and fatigue tests were carried out respectively in different loading rates. The yield surface of strength for asphalt mixture was put forward based on the strength tests results and the yield criterion. Then, the normalization model of fatigue characteristics for asphalt mixtures under different stress states was established based on the yield criterion in 3 dimensional stress states. The results show that the differences of the fatigue tests results of asphalt mixtures under different test condition are large. It is difficult to evaluate the fatigue performance in different stress states of asphalt mixtures by using the conventional S-N fatigue equation. However, these differences can be reduced or even eliminated by using the normalization model, which considered the influence of the stress state and the strength corresponding to the fatigue loading frequency and stress level. The unified expression of fatigue characteristics under different test conditions for asphalt mixtures was realized. The fatigue behavior of asphalt mixture under different stress conditions can be objectively evaluated by using the normalized model. [ABSTRACT FROM AUTHOR]

In order to explore the moduli decay patterns of asphalt mixtures under different loading conditions, the nonlinear fatigue damage model was implemented in order to simulate the moduli decay patterns. Then, the direct tensile, indirect tensile, and uniaxial compression fatigue tests were employed under four kinds of stress levels with four parallel tests. The specimens of AC-13C Styrene-butadiene-styrene (SBS) modified mixtures were manufactured. Based on the test results, the decay patterns of the moduli during fatigue tests under different stress states were revealed, and the parameters of the damage model under different test conditions were obtained. By changing the values of the model parameters under a certain loading condition, fatigue curves were obtained. Then, the fatigue properties of asphalt mixtures under different stress states could be compared and analyzed directly. The result indicated that the evolution curves of fatigue damage for the direct tensile test, the indirect tensile test, and the uniaxial compression test all experienced three stages, which indicates that the fatigue damage characteristic of asphalt mixtures is non-linear. The decay patterns of the direct tensile moduli and the tensile moduli measured by the indirect tensile test are similar. The decay patterns of the uniaxial compression and the compression moduli measured by indirect tensile test are similar. The decay patterns of tensile and compressive moduli are obviously different. At the same cycle ratio state, the position of the decay curve for the compression moduli is higher than that of the tensile moduli. It indicates that the tensile failure is the main reason of the fatigue damage for asphalt mixture. The new analysis method of fatigue damage was proposed, which provides a possibility to compare the fatigue results that were obtained from different loading conditions and different specimen sizes. [ABSTRACT FROM AUTHOR]

Two new test methods were proposed to measure the different moduli of asphalt mixtures simultaneously based on four-point bending and indirect tensile tests. The new calculating formulas were derived for tensile and compressive moduli of asphalt mixtures under four-point bending loading model, which combining the equilibrium condition and the plane hypothesis in elastic mechanics theory. Meanwhile, on the basis of the test principle of indirect tensile moduli and Hooke’s law in two-dimensional stress states, the new calculating formulas were derived in indirect tensile loading model. The moduli tests of four-point bending, indirect tensile, direct tension and unconfined compression were carried out separately to verify effectiveness of the new methods. The results of tensile and compressive moduli from the two new methods were compared with the direct tension moduli tests and unconfined compression moduli tests. The correlations among them were analyzed. The result indicates that the tensile and compression moduli of asphalt mixtures show a significant difference, and can be obtained by two methods simultaneously. The two new methods realize the synchronous measuring of various moduli of asphalt mixtures. [ABSTRACT FROM AUTHOR]

• The strength properties of asphalt mixture with different gradation curves were evaluated. • A unified fatigue model was developed based on the fatigue stress strength ratio. • The gradation curve of asphalt mixture with the optimal strength and fatigue performance was determined. The gradation design has an essential influence on the mechanical properties of asphalt mixture. Strength and fatigue are two critical mechanical properties of asphalt pavement structure. The purpose of this paper is to reveal the strength and fatigue properties of asphalt mixture with four gradation curves within the range of AC-16, namely Types A, B, C, and D. Strength and fatigue tests were conducted under indirect tensile, direct tensile, and unconfined compressive loading modes. The strength of asphalt mixture with various gradation curves shows a power function relationship with the loading rate. The fatigue performance of asphalt mixture with different gradation curves was first analyzed based on the conventional S-N fatigue model. Then, the unified fatigue models under three different loading modes were established based on the fatigue stress strength ratio, which reduced the difference of S-N fatigue equation parameters. Furthermore, the unified fatigue equations achieved the unity of strength failure and primary fatigue failure. The analysis results indicate that the mixture with Type D gradation curve realizes the highest strength and most extended fatigue life. This research contributes to the gradation design of asphalt mixture. And the unified fatigue equation provides a reference for the durability design of pavement. [ABSTRACT FROM AUTHOR]

Due to the high viscosity of high-content rubber modified asphalt, maintaining a high temperature for a long time is required when preparing rubber modified asphalt mixtures. This problem limits the attainment of ideal conditions in experimental research. Using the bio-oil could reduce the viscosity of rubber modified asphalt and thus reduced the mixing temperature of its mixtures. The objective of the manuscript is to propose production protocol of bio-oil rubber modified asphalt mixture (BRMAM) and evaluate its performance. The rubber (20 % mass ratio of modified asphalt) and bio-oil (5 % and 10 % mass ratio of modified asphalt) were used to prepare two types of the BRMAM under lower mixing temperature. The high-temperature stability, low-temperature anti-cracking, water stability and other mechanical performance were appraised. Based on the test results, the total deformation of the BRMAM decreased by 39.4 %, the Marshall modulus increased by 45.5 % compared to the neat asphalt mixture, and their fracture energy increased by 36.27 %. Under the condition of high stress ratio, the fatigue life of modified asphalt mixture rose by 32.4 %. The addition of crumb rubber could enhance the elastic recovery of BRMAM. The synergism of the bio-oil and crumb rubber could lower the mixing temperature without sacrificing the performance. This study provides a basis for BRMAM in the laboratory and field applications or similar scenarios. The study could contribute to the recycling of renewable resources and the reduction of carbon emission. • Proposed lower temperature bio-oil rubber modified asphalt mixture production method. • Evaluated the performance of the bio-oil rubber modified asphalt mixture. • Get the optimal bio-oil and rubber content combination. [ABSTRACT FROM AUTHOR]

In order to describe the fatigue damage state of asphalt mixture more reasonably, direct tensile tests of the fatigue and the residual strength under stress levels of 1.00 MPa, 0.50 MPa and 0.25 MPa with five parallel tests were carried out. The trabecular specimens of AC-13C asphalt mixture (25 cm × 5 cm × 5 cm) were manufactured with Styrene-Butadiene-Styrene (SBS) modified asphalt, aggregate basalt and limestone mineral filler. The optimum asphalt-aggregate ratio was 5.2%. The dynamic modulus decay and the residual strength decay were termed as the damage variables to evaluate the fatigue damage process of asphalt mixtures, respectively. Based on the test results, the decay patterns of the dynamic modulus and the residual strength during fatigue tests under different stress states were revealed, and the model and the parameters of fatigue damage according to the corresponding decay patterns were obtained. Then, based on the assumption that the residual strength and dynamic modulus depend on the same damage state, the relationship between the two damage definitions was given, and the residual strength-dynamic modulus coupled model was established. The results showed that the residual strength-dynamic modulus coupled model could better describe the fatigue damage evolution law of asphalt mixture, and the parameter of this coupled model could be obtained by less residual strength tests. A modified formula for calculating the damage variables associated with residual strength and dynamic modulus was proposed based on the relationship between two kinds of damage variables. [ABSTRACT FROM AUTHOR]

Although the rutting resistance, fatigue cracking, and the resistance to water and frost are important for the asphalt pavement, the strength of asphalt mixture is also an important factor for the asphalt mixture design. The strength of asphalt mixture is directly associated with the overall performance of asphalt mixture. As a top layer material of asphalt pavement, the strength of asphalt mixture plays an indispensable role in the top structural bearing layer. In the present design system, the strength of asphalt pavement is usually achieved via the laboratory tests. The stress states are usually different for the different laboratory approaches. Even at the same stress level, the laboratory strengths of asphalt mixture obtained are significantly different, which leads to misunderstanding of the asphalt mixtures used in asphalt pavement structure design. The arbitrariness of strength determinations affects the effectiveness of the asphalt pavement structure design in civil engineering. Therefore, in order to overcome the design deviation caused by the randomness of the laboratory strength of asphalt mixtures, in this study, the direct tension, indirect tension, and unconfined compression tests were implemented on the specimens under different loading rates. The strength model of asphalt mixture under different loading modes was established. The relationship between the strength ratio and loading rate of direct tension, indirect tension, and unconfined compression tests was adopted separately. Then, one unified strength model of asphalt mixture with different loading modes was established. The preliminary results show that the proposed unified strength model could be applied to improve the accurate degree of laboratory strength. The effectiveness of laboratory-based asphalt pavement structure design can therefore be promoted. [ABSTRACT FROM AUTHOR]

Modulus testing methods under various test conditions have a large influence on modulus test results, which hinders the accurate evaluation of the stiffness of asphalt mixtures. In order to decrease the uncertainty in the stiffness characteristics of asphalt mixtures under various stress states, the traditional unconfined compression test, direct tensile test, and the synchronous test method, based on the indirect tension and four-point bending tests, were carried out for different loading frequencies. Results showed that modulus test results were highly sensitive to the shape, size, and stress state of the specimen. Additionally, existing modulus characteristics did not reduce these differences. There is a certain correlation between the elastic modulus ratio and the frequency ratio for asphalt under multiple stress states. The modulus, under multiple stress states, was processed using min–max normalization. Then, the standardization model for tensile and compressive characteristics of asphalt under diverse stress states was established based on the sample preparation, modulus ratio variations, and loading frequency ratio. A method for deriving other moduli from one modulus was realized. It is difficult to evaluate the stiffness performance in diverse stress states for asphalt by only using conventional compressive and tensile tests. However, taking into account the effects of stress states and loading frequencies, standardized models can be used to reduce or even eliminate these effects. The model realizes the unification of different modulus test results, and provides a theoretical, methodological, and technical basis for objectively evaluating moduli. [ABSTRACT FROM AUTHOR]

• The stress ratio was redefined based on the strength failure envelope line under multi-field coupling conditions. • The unified model of fatigue performace under various stress states, temperatures, and loading frequencies were proposed. • The dispersion caused by different methods and test conditions can be eliminated by the unified fatigue model. For a scientific and reliable design of asphalt mixture subjected to fatigue damage, a comprehensive understanding and realistic prediction of asphalt mixture fatigue life under complex loading conditions with variable loading rates or temperature were a major concern. In this study, direct tensile test, uniaxial compression test, indirect tensile test, and four-point bending test were used to study the fatigue behavior of asphalt mixtures with a particular focus on the action of temperature and frequency. Strength and fatigue were investigated separately under varied loading rates at several temperatures. A new idea for determining the stress ratio based on the strength failure envelope line considering temperature and loading rate was proposed. The connection between strength and fatigue was established by the stress ratio. The test conditions for strength and fatigue tests were set to be the same leading to the fatigue data distributed regularly. Experimental data were analyzed and normalized by studying the evolution of the number of cycles with the stress ratio. A new analytical approach was introduced to simulate the fatigue performance. The fatigue performance under multi-field coupling conditions was uniformly characterized. The dispersion of fatigue equation caused by the test method and conditions is eliminated. Engineering application showed that the design deviation of the pavement fatigue resistance was reduced to less than 6%. [ABSTRACT FROM AUTHOR]

In the actual service process of asphalt pavement, the dynamic response of the pavement structure layer is induced by vehicle loads. The dynamic modulus is a crucial parameter for analyzing the mechanical response of asphalt pavement. Due to significant influences from temperature and loading frequency on test measurements, along with its time-temperature equivalence, it becomes imperative to investigate the behavior of dynamic modulus under different temperature frequencies. Furthermore, laboratory loading modes also exert substantial effects on dynamic modulus. Employing different loading modes during measurement often leads to significantly varied stress states in specimens, yielding distinct values for dynamic modulus. Therefore, this study conducts dynamic modulus tests using direct tension, uniaxial compression, and indirect tension under five test temperatures and six loading frequencies while examining its variations under different stress states and temperature frequencies. The corresponding master curves and prediction models of dynamic modulus are derived, providing a valuable reference for predicting the dynamic modulus under wide-area test conditions. Through comparative analysis of dynamic modulus values at different stress levels, the stress level is incorporated into the master curve to establish corresponding master curves of dynamic modulus. By applying relevant theories and research on time-temperature equivalence, we obtained dynamic modulus master curves for three loading modes by fitting and analyzing dynamic modulus test data at various temperatures and loading frequencies. Combining the Sigmoid model and Williams-Landel-Ferry(WLF) equation, we derived prediction models for dynamic modulus under three loading modes. Comparative analysis of dynamic modulus values under these three loading modes allowed us to establish transformation equations for the prediction models in different loading scenarios. Finally, representative dynamic modulus values for permanent deformation in typical pavement structure layers were predicted based on laboratory test results and the derived models. The research findings presented in this paper have significant implications in eliminating the influence of loading modes on dynamic modulus predictions, establishing a unified prediction model, and providing essential parameters for predicting permanent deformation and fatigue life equivalent temperature. • Introducing stress level variables into the dynamic modulus master curve. • Extending the two-dimensional dynamic modulus master curve to three-dimensional master surface. • Derived the conversion equations between prediction models for different loading methods. [ABSTRACT FROM AUTHOR]

• Asphalt mixture containing high-proportion RAP was prepared by SMC regenerant. • The failure strength master curve of high-content RAP asphalt mixture was obtained. • The fatigue performance of high-proportion RAP asphalt mixture was studied. Reclaimed Asphalt Pavement (RAP) is a cleaner production widely used in road engineering. In order to investigate the failure strength and long-term performance of high-proportion RAP asphalt mixture, this research prepared two high-content RAP recycled asphalt mixtures (50% and 60% RAP-RAM) with the gradation of AC-20 based on Styreneic Methyl Copolymer (SMC) regenerant. Firstly, indirect tensile (IDT) strength tests were implemented on 50% and 60% RAP-RAM at four temperatures and six loading rates. Secondly, IDT fatigue tests at six stress levels were carried out. The relationships of strength and temperature, strength and loading rate were obtained based on strength test results. The master curve model of indirect tensile strength and loading rate of high-proportion RAP recycled asphalt mixture was established by linear and Sigmoidal functions. On the basis of the Sigmoidal strength master curve equation, the fatigue stress ratio was calculated. Finally, this paper established the fatigue equation of the high-content RAP recycled asphalt mixture based on the fatigue stress ratio. The analysis results show that 50% and 60% RAP-RAM based on SMC regenerant show favorable strength and fatigue properties. In addition, increasing the proportion of RAP improves the strength of the mix while reducing the loading rate sensitivity of strength. However, the fatigue performance of the mix reduces by increasing RAP content. The fatigue equation based on the fatigue stress ratio takes the factors of temperature and loading rate into account, reflecting the mix's fatigue performance more realistically. The strength and fatigue performance results verify the reliability of the high-content RAP recycled asphalt mixture based on SMC regenerant and provide a reference for the effective utilization of RAP which can generate environmental benefits of saving aggregate and asphalt and reducing energy consumption and carbon emissions. [ABSTRACT FROM AUTHOR]

• The relationship among asphalt mixture strength, loading rate and temperature was revealed. • The strength characteristics of four asphalt mixtures were compared and analyzed.. • The modified asphalt mixture strength master curve was established.. Bio-asphalt mixture is prone to strength damage due to its unfavorable high-temperature performance and anti-aging properties. In order to improve the strength of the bio-asphalt mixture, this paper selected rock asphalt to modify bio-asphalt and studied the strength characteristics of rock asphalt modified bio-asphalt mixture. First, the neat asphalt mixture, rock asphalt modified asphalt mixture, bio-asphalt mixture, and rock asphalt modified bio-asphalt mixture were prepared. After that, the indirect tensile strength (ITS) tests at different temperatures and various loading rates were conducted. Based on the test results, linear function and Sigmoidal function were used to establish prediction models of four asphalt mixtures strength. Finally, the strength behavior of four asphalt mixtures was compared and analyzed according to the master curve. The test results indicated that the strength of the four asphalt mixtures increases with the increase in the loading rate and decreases with the increase in the temperature. Compared with the bio-asphalt mixture, the strength of the rock asphalt modified bio-asphalt mixture was better, proving the feasibility of the rock asphalt modification technology. Compared with the linear function, the master curve determined by the Sigmoidal function is smoother. The fitting correlation coefficient by the Sigmoidal function is higher than that by the linear function. The strength prediction model proposed in this study can effectively predict the strength of the asphalt mixture outside the test range through limited test data, which provides a test basis for applying bio-asphalt mixture in pavement design under different climate and traffic load conditions. [ABSTRACT FROM AUTHOR]

• A failure criterion model in the strain space was established by the convention method based on the generalized Hooke's law. • The linearized calculation model of resilient modulus was established by the resilient modulus tests in complex stress state. • The strain failure criterion model considering the effect of stiffness was established. In order to reveal the effect of complex stress state on the characteristics of strength and stiffness of asphalt mixture, the self-developed double confining pressure triaxial test method was used in this study. The one-time failure and resilient modulus tests in complex stress state were carried out on the SMA-13 and AC-13 asphalt mixtures widely used in China's asphalt pavement, especially in the combined tensile-compressive stress state. The failure principal stress of material and its stress-strain data under the step loading condition were obtained. The calculation model of resilient modulus in complex stress state and the failure criterion I 1 - J 2 in the principal stress space were established. On this basis, based on the generalized Hooke's law, a three-dimensional strain failure criterion model for asphalt mixture considering the effect of stiffness was also established by the conversion method. The research results can provide experimental and theoretical support for the reasonable selection and resistance calculation of material parameters of asphalt mixture in complex stress state. [ABSTRACT FROM AUTHOR]

• A damage model considering the interaction between fatigue and creep was established. • The model could reflect the effect of stress level on the damage evolution process. • The nonlinear characteristics of damage evolution could be well-reflected. To describe the interaction of fatigue-creep damage of an asphalt mixture under the action of semi-sine cyclic loading reasonably, a direct tension fatigue test was carried out under four different stress levels (0.5, 1, 1.5, and 2 MPa) based on the fact that semi-sine fatigue stress can be decomposed into creeping stress and simple fatigue stress. In addition, tension-compression fatigue and static creep tests were carried out under four stress levels: 0.25, 0.5, 0.75, 1 MPa. For each test, five parallel tests were carried out at the same stress level. The Chaboche fatigue damage model and Kachanov creep damage model were employed to evaluate the damage evolution of the mixture both in the fatigue and creep tests. According to the test results, the damage evolution trends were revealed under different test processes and stress levels, and the damage evolution models of three different test methods were obtained. Then, based on the principle of semi-sine fatigue stress decomposition, a fatigue-creep damage interaction model considering the interaction of fatigue and creep damage was established using normalized parameters (X = N / N f = t / t R) as the intermediate variable. The results indicated that the damage of asphalt mixture under the action of the semi-sine cyclic load was not a simple linear accumulation of fatigue damage and creep damage, but an overall result of the interaction of fatigue damage, creep damage, and fatigue-creep damage. The fatigue-creep damage interaction model provided a good fit with the experimental data and showed a high degree of consistency with the classical damage model. The model could be used to describe the damage evolution trend of asphalt mixture under the action of semi-sine cycle load and the interaction effect of fatigue damage and creep damage. [ABSTRACT FROM AUTHOR]