Behavior Of Asphalt Mixtures Research Articles

Impact of Aging and Moisture on Fatigue Life of Asphalt Mixture

Abstract In this study, the mechanical behavior of a dense-graded asphalt mixture subjected to unaged, short-term, and extended aged conditions along with one freeze-thaw moisture conditioning cycle was evaluated at two temperatures and three stress magnitudes. A stress-controlled repeated indirect tensile loading fatigue test with 0.1-s loading and a 0.4-s rest period was used for determining the fatigue life of asphalt mixture. Aging, moisture conditioning, and an increase in the test temperature adversely affected the tensile strength of the asphalt mixture. The reduction in stiffness modulus of asphalt mixture that was due to moisture conditioning increased with the increase in the level of aging. The ratio of conditioned to unconditioned stiffness modulus (stiffness modulus ratio) was noticed to be more sensitive to different aging conditions compared with the ratio of conditioned to unconditioned tensile strength (tensile strength ratio). The effect of aging on fatigue life of asphalt mixture reduced with the increase in stress from 450 kPa to 550 kPa and 650 kPa. Further, the fatigue life of asphalt mixture reduced with the increase in test temperature and moisture conditioning. The short-term and extended aged mixture had higher damage value at failure compared with the unaged mixture. The mean fatigue life represented by the scale parameter of Weibull distribution reduced with the increase in aging and moisture conditioning. Further, the reliability of fatigue life of short-term aged and extended aged asphalt mixture was lower than the unaged asphalt mixture. The fatigue model based on plateau value and fatigue life was found to be more accurate compared with other regression models considered. Statistical analysis showed that the critical combinations of factors that influenced the mechanical behavior of asphalt mixture were also dependent on the test type, which included the tensile strength test, stiffness test, and fatigue test.

Evaluation of the Performance of a Warm Mix Asphalt (WMA) Considering Aged and Unaged Specimens

In the last decades, all technology production sectors reached a high level of development, without neglecting the attention to environmental aspects and safeguarding energy resources. Moreover, in the sector of pavement industry, some alternatives of bituminous mixtures were proposed to reduce the greenhouse gas emissions. One of these is the warm mix asphalt (WMA), a mixture produced and compacted at lower temperatures compared to traditional hot mix asphalt (HMA) (about 40 °C less), to allow a reduction of emissions into the atmosphere and the costs. Other operative benefits concern the health of workers during the whole road construction process, the reduction of distances to which the mixture can be transported, and therefore also the positioning of the plants. However, it is not all benefits, since reduced production temperatures can bring short- and long-term water sensitivity issues, which could threaten the pavement performance. This paper evaluated the performance (water sensitivity, stiffness, fatigue, and permanent deformation) of a WMA produced using a warm mix fabrication bitumen and compared it with an HMA tested in parallel. In general, except for the resistance to permanent deformation, the WMA presented performances comparable to HMA. Regarding the fatigue behavior of asphalt mixtures, the WMA was less affected by ageing conditions, despite it showing lower performance than HMA.

Effects of specimen size and loading conditions on the fracture behaviour of asphalt concretes in the SCB test

The semi-circular bending (SCB) test has gained popularity for cracking evaluation of asphalt concrete due to its simplicity in the test setup and sample preparation. The current standards for the SCB test, such as EN 12697-44:2010, AASHTO TP 105-13, ASTM D8044-16, and ASSHTO TP 124-18, utilise 150 mm as the standard diameter for test samples. Recently, the 100 mm diameter was investigated and its applicability for use in the SCB test was confirmed. However, investigation of factors affecting the fracture behaviour of 100 mm diameter samples, such as loading rate, temperature, and aggregate size, is still limited. As yet, no comparison of the SCB fracture performance of 100 mm diameter and 150 mm diameter samples (e.g. fracture toughness, fracture energy, cracking indexes) is available for the nominal maximum aggregate size (NMAS) of 10 mm or larger. Furthermore, conversion of results from the two diameters is not yet available. For applications of the 100 mm samples in parallel with the 150 mm samples, comparisons and conversion of the fracture properties obtained from the two sample sizes are significant. This study was performed to fulfil that purpose. Both SCB sample diameters were prepared with three different thicknesses of 30, 40 and 50 mm, using different NMAS of 10, 14 and 19 mm. The SCB samples were tested at four different loading rates of 0.5 mm/min, 1 mm/min, 5 mm/min and 10 mm/min, and at two temperatures of 25 °C and 10 °C. The study investigated fracture properties including fracture toughness, fracture energy, and cracking indexes such as the flexibility index and the cracking resistance index. The results showed that the fracture toughness for the two diameters was similar, while the fracture energy obtained from the 100 mm samples was roughly 21% less than that achieved from the 150 mm samples. The cracking resistance index results obtained from the 150 mm samples were approximately 8% higher than those obtained from the 100 mm samples. The flexibility index from both diameters showed low correlation. The overall result suggested that the SCB test with 100 mm samples can be used to evaluate the fracture behaviour of asphalt mixtures with NMAS up to 19 mm, and the fracture properties obtained from the two different sample sizes are convertible.

Determination of the permanent deformation of hot mix asphalt with natural desert sand

This study attempts to evaluate the permanent effects of using natural desert sand (NDS) on the behaviour of asphalt mixtures. Previous studies have focused on the characterization of permanent properties of asphalts that use NDS. This study aims to determine the effect of using fine aggregate materials NDS and manufactured crushed sand (MCS) in hot mix asphalt (HMA) and how this affects the permanent deformation of the final HMA. The NDS samples were collected from the desert regions. The Index of Aggregate Particle Shape and Texture (IAPST), Marshall, the Rutting analyzer and the Complex Modulus tests were undertaken to analyze and compare the properties of HMA containing two different types of bitumen binders, PG70-10 and B60/70. The performance of mixtures containing PG70-10 was found to be superior in comparison with mixtures containing B60/70. These results are critical for engineers planning roadworks in hot and arid environments and allow for significant cost reductions by using locally available materials (i.e. NDS) instead of more costly MCS. With these findings, it is possible to partly use NDS in HMA for low volume roads (LVRs).

Meso-structure image pre-selection method for two-dimensional finite element modeling in beam bending simulation of asphalt mixture

Finite element (FE) simulation has been widely used in conjunction with the beam bending test (BBT) to analyze the cracking behavior of asphalt mixtures. Crack propagation is significantly affected by the internal structure of an asphalt mixture. Limitations on computational resources and the complex mesostructure of asphalt mixtures have resulted in two-dimensional (2D) FE simulations being more widely used than three-dimensional simulations. However, a single 2D FE model can only reflect the mesostructural characteristics of one specimen section, precluding comparison between the simulation and laboratory test results. In this paper, X-ray CT scanning technology was used to obtain a large number of internal mesostructure images of an asphalt mixture, and image-based modeling was used to construct 2D FE models for simulating beam bending tests. An analysis of the simulated crack morphologies and positions of the models was used to propose a prediction method for the crack position based on image processing technology, and a hypothesis that the crack positions were correlated with the simulation results was put forward. This hypothesis was verified by comparing the simulation and laboratory test results. Finally, the predicted crack position (CPRP) was used to propose an image preselection method from which 2D FE models were constructed to simulate of BBT for an asphalt mixture. This method considerably reduces the number of 2D FE models required and significantly improves the calculation efficiency while ensuring the accuracy of the BBT 2D simulations.

Laboratory assessment of the performance and elastic behavior of asphalt mixtures containing steel slag aggregate and synthetic fibers

This study focused on the assessment of the performance of fiber-modified asphalt mixtures containing steel slag aggregates. The asphalt mixtures incorporating coarse steel slag aggregate were reinforced with three types of synthetic fibers polyvinyl alcohol, acrylic and polyester at the dosage of 0.3% by weight of the aggregates. The performance tests were resilient modulus, rutting resistance, moisture sensitivity and cracking resistance. The results showed that the resilient modulus of the reinforced mixtures was slightly lower than the reference mixtures at all frequencies. Additionally, the rut depth of the reinforced mixtures was lower than the reference mixtures due to the densification. Otherwise, the reinforced asphalt mixtures showed better resistance to rutting than the control mixtures after excluding the deformation caused by the densification. The indirect tensile strength and tensile strength ratio of the reinforced asphalt mixtures were higher than the mixture containing steel slag aggregate. The cracking resistance of the reinforced mixture was the best in comparison with the other mixtures at the applied load at the high frequencies. While the reinforced asphalt mixtures showed the worst resistance to cracking at the applied load with low frequency of 2.5 Hz.

Effect of Using Anti-Stripping on Fracture Behavior of Asphalt Mixtures Using Linear Elastic Fracture Mechanic (LEFM) Technic

Today, cracking asphalt pavement in low temperature is one of the obstacles for protecting pavement in the cold climates. One of important factors in extending of these types of cracking is cooling and heating temperature cycles according to the changes in seasons. Therefore, this research examines these types of asphalt cracking by considering asphalt mixtures and using mechanics science. In this research, cold environmental conditions were determined by making asphalt gyratory asphalt samples and fracture test in -15°C to study the effect of asphalt mixtures important parameters, it means asphalt construction materials textile on fracture resistance of samples. On the other hand, simultaneous effect of two parameters on asphalt fracture resistance was examined by considering the effect of freezing and thawing cycles, as well as using siliceous and calcareous materials. In addition, the effect of this material was studied to improve asphalt properties and fracture resistance by introducing antistripping material.

Study on Creep Behavior Of Asphalt Mixture Based on Discrete Element Method

A three-dimensional (3D) microstructure-based discrete element (DE) model was developed to study the creep behaviour of high viscoelastic asphalt sand (HVAS) with the uniaxial compression creep tests. The three-point bending creep tests of asphalt mortar were carried out in order to obtain the parameters of the Burger model, to determine the transformation method of macroscopic parameters and microscopic parameters of the model in theory, to obtain the parameters used in the discrete element model, and then establish the discrete element analysis model for the asphalt mixture. A 3D-DE digital specimen was composed of coarse aggregates, asphalt mortar and air voids, which could also take gradation, irregular shape, random distribution of aggregate and air voids into consideration, and the boundary conditions of the model were set through the simulation of the uniaxial compression creep tests. An accurate and extensive mapping model of HVAS was built by 3D-PFC (Particle Flow Code), which can provide a simple alternative to the laboratory tests. This method can simulate a series of numerical examples based on different stress levels, coarse aggregate homogenizations, mortar homogenizations and temperatures in a single factor method. Comparison of results of laboratory and numerical tests shows that the 3D-PFC-viscoelastic model can reflect the creep mechanical behaviour of asphalt mixture accurately. It provides the theoretical basis and auxiliary means for analysing the mechanical properties of asphalt mixtures using PFC software. The research on creep behaviour of the asphalt mixture by numerical simulation opens up a new way for the research on creep behaviour of the asphalt mixture, it is of considerable theoretical value and has broad application prospects.

Analysis of interface interaction of aggregate-asphalt system and its effect on shear-slip behavior of asphalt mixture

The interface interaction of aggregate-asphalt system is a key factor affecting the strength formation and deterioration of the asphalt mixture, which has a great influence on the distress and durability of pavement. To analyze the influence of the interface interaction of aggregate-asphalt system on the shear-slip behavior of asphalt mixture, two self-developed testers were adopted to measure the parameters of particle contact and interface shear-slip, and the effective evaluation methods were proposed on the mesoscopic level. The results indicate that the interface interaction is from the coupling effect of the particle contact and the bonding and lubrication of asphalt. Among involved aggregate-asphalt systems, the AC-13L system has a strong contact strength, while its skeleton structure is easily affected by the lubrication of asphalt. The contact and interaction parameters of involved aggregate-asphalt systems except for AC-13L exhibit a good linear correlation with the shear-slip parameters of asphalt mixtures. The AC-20M system has the strongest contact effect and easily forms a multilevel dense interlocking structure interacting with asphalt, which shows the best resistance to shear-slip deformation. The interference of fine aggregates and the lubrication of asphalt can adversely affect the resistance to slip deformation of asphalt mixtures.

Study on Dynamic Modulus Dependence Model for Asphalt Mixture Based on Temperature and Strain Parameters

In order to objectively characterize the nonlinear viscoelastic behavior of asphalt mixture and its dependence on temperature and load, the two-point dynamic flexural tensile modulus test of asphalt mixture at different strain levels, temperatures and loading frequencies is carried out by using French trapezoidal beam tester. By introducing the method of nonlinear operator, the dynamic modulus dependency modeling method for asphalt mixture based on temperature and strain parameters is put forward, the expression of dynamic modulus principal surface of asphalt mixture is established, and the reliability of the dynamic modulus dependent model is evaluated by correlation coefficient test and variance analysis method. The result shows that (1) for the two-point flexural tensile test of trapezoidal beam based on asphalt mixture of full-scale test track, the mean values of dynamic modulus variation coefficient at 0℃ and 45℃ are about 2.5% and 6.2% respectively, the mean values of dynamic modulus variation coefficient at 10 test temperatures is about 4%, the variation level of the test method is low, the error is small, which has a very good parallelism and reliability; (2) for the established dynamic modulus dependent model expression based on temperature and strain parameters, the decision coefficient R2 can reach more than 0.99, the P value of F test is 0, the fitting effect of the model on the test result is good, and there is a significant correlation of dynamic modulus with temperature and strain level; (3) the model can be used to describe the dynamic flexural tensile modulus of asphalt mixture, and the description model of the dynamic modulus can be transformed from principal curve to principal surface. In pavement structure analysis, this model can reflect the nonlinear response phenomenon in actual pavement more objectively, and can avoid the problems such as distortion of the calculation result caused by unreasonable modulus value in structural analysis effectively.

Study of the permanent deformation of binders and asphalt mixtures using rheological models of fractional viscoelasticity

The accumulation of load on asphalt pavement as a result of increased vehicle traffic generates problems in the asphalt layer due to permanent deformation. For correct design, it is essential to carry out a rheological characterization of the aggregate-binder materials that make up the asphalt mix. This article shows the analysis of permanent deformation based on the rheological behavior of asphalt mixtures and binders. Experimental tests based on creep and recovery phenomena allow the study of permanent deformations using theoretical models of fractional viscoelasticity. The rheological characterization allows us to detail the elasticity of the aggregate, ξ2, and the elastic-viscous properties of the different binders used, ξ1 and η. The results obtained show that it is possible to predict the deformations of the recovery phenomenon in asphalt mixtures from the rheological values (aggregate-binder) obtained in the creep process. Besides, the properties of the asphalt binder (ξ1 and η) correlate with the recovery phenomenon of the MSCR test for conventional and modified materials. The methodology proposed allows a better understanding of the states of permanent deformation to improve the design of binders and asphalt mixtures.

Shear Deformation Behavior of a Double-Layer Asphalt Mixture Based on the Virtual Simulation of a Uniaxial Penetration Test.

This paper aims to clarify the shear deformation behavior of double-layer asphalt mixtures using the virtual uniaxial penetration test (UPT) with a discrete element method. For this purpose, asphalt mixtures with two different nominal maximum aggregate sizes were designed for the preparation of double-layer wheel tracking test specimens. Then, the cylindrical cores were prepared from the specimens and were cut for capturing the longitudinal profile images. These images were used to reconstruct a two-dimensional discrete element model (DEM) of the uniaxial penetration test specimen. The results indicate that the shear deformation behavior of the asphalt mixtures showed corresponding changes under the virtual loading. The tensile and compressive stress were distributed unevenly within the upper layer after the test, and both coarse aggregates and asphalt mortars bore a greater shear stress. Therefore, cracks were more likely to occur in the upper layer, leading to the failure of the specimens. This process enhanced the bonding between the asphalt mortars and the mineral aggregates. The aggregate particles in the upper layer moved more vertically, while those in the lower layer generally moved more laterally under the virtual loading. This behavior reveals the rutting mechanism of asphalt pavement.

Study of the influence of the loading rate on the fracture behaviour of asphalt mixtures and asphalt mortars

Proper fracture characterization of Hot Mix Asphalt (HMA) is crucial to enhance the durability of pavement structures. This work evaluates the influence of the loading rate on the fracture behaviour of a typical dense-graded asphalt mixture and its correspondent mortar or Fine Asphalt Mixture (FAM). Semi-Circular Bending (SCB) tests were conducted under intermediate temperature (24 ± 1 °C), and six different loading rates (i.e., 0.1, 0.5, 5, 10, 25, 50 mm/min). The results show that neither the three-dimensional cracked surface area of the fracture zone of the FAM and HMA samples nor the resistance to crack propagation of the materials were loading rate-dependent, whereas its fracture energy, strength and stiffness were sensitive to this testing condition. Significant differences were also observed in the magnitudes of all cracking parameters within the full mixture and its mortar, as expected, except for the stiffness of the materials.

Discrete Element Analysis of Indirect Tensile Test Based on Image Processing with Annular Segmentation and Bimodal Threshold

Abstract The discrete element method (DEM) has recently been widely used to analyze the micromechanics behavior of asphalt mixtures. The objective of this study is to present a more accurate image-processing technique to perform an indirect tensile test of asphalt mixture. Cross-sectional images of the specimen were obtained by an X-ray computed tomography (CT) technique. These CT images were processed by annular segmentation combined with bimodal threshold. The image information was transformed to coordinate information by the user-defined program in Matrix Laboratory (MATLAB). Then, a two-dimensional discrete element model of the indirect tensile test specimen was reconstructed. The indirect tensile test was simulated by the DEM and verified in the laboratory. It was found that this image-processing technology could separate connected or overlapping aggregates and better avoid defects among the aggregates. During the simulation test, the distributed internal forces were gradually concentrated along the loading axis. Four-stage crack initially appeared directly under the loading area and quickly developed along the interface between the aggregate and mortar, mainly along the loading axis. In view of the consistency of the load–displacement curves and crack distribution characteristics in both the simulation and laboratory tests, this numerical method is able to simulate the indirect tensile test.

Enhanced asphalt mixture behavior by using khawa clay to resist deformation

This paper aims to investigate the effect of adding bentonite (khawa clay) on the asphalt mixture response represented by reducing total accumulative deformation. Asphalt cement with penetration grade of (40-50) and optimum asphalt content of 4.9 was used. Bentonite with different percentages of (0%, 3%, 6%, and 9% by total weight of asphalt cement) was used. The asphalt mixtures were tested by uniaxial creep test under static load at two test temperature (40°C and,60°C) and the applied stress used 600 KPa. From the experimental result of rotational viscosity after and before the addition of bentonite at two temperatures 135°C and 165°C, it can be seen that the viscosity of the asphalt cement was enhanced when adding 9% of Khawa clay to around 126% percent of improvement in viscosity at 135°C and about 195% at 165°C. The improvement in the viscosity of asphalt leads to a decrease in the accumulative strain.

Experimental and Theoretical Investigation on the Effect of Carbon Nanotubes on Flexible Pavement

One of the most recently application for pavement performance improvement is the application of nonmaterial technology. The objectives of this research are to study the beneficial effect of using Nano Carbon Tube (NCTs) on the behaviour of asphalt mixture as preliminary indications and on the performance behaviour of flexible pavement system as a final investigation. The obtained experimental and finite element modelling results showed that adding (0.1%) and (1%) NCTs improved the stability value of asphalt mixture about (15%) and the addition of 0.5 % reduced the flow value around (2%) which means providing enhancement for rutting resistance. High elastic modulus value of (14000 MPa) are obtained at (0.5%) NCTs. This demonstrated the significant improvement of mechanical properties of modified asphalt mixtures as compared with control mix. The experimental results demonstrated the beneficial applications of carbon nanotubes NCTs additives to minimize the effect of moisture susceptibility for hot asphalt mixtures at (0.1%). The modified asphalt mixture with NCTs decreased the resistance to fatigue damage life of flexible pavement at (0.1%) and (0.5 %) NCTs but provide improve the fatigue resistance by about (10%) at (1%) NCTs and improved the resistance to rutting damage significantly about (83%), (233%), and (250%) for (0.1%), (0.5%) and (1%) NCTs respectively.

Analysis of deformation behavior and microscopic characteristics of asphalt mixture based on interface contact-slip test

To analyze the slip deformation behavior of asphalt mixture, an interface contact-slip tester of asphalt mixture was developed in this investigation. Four evaluation indicators, including the maximum slip shear stress τsl, the slip shear strain εS, the slip failure modulusES and the interface slip energy index ET, were proposed. According to the correlation and sensitivity analysis, the optimum evaluation indicator was determined. By analyzing the variation coefficient of test results, the key experiment parameters were recommended. The gray binarization method of MATLAB software was adopted to process the slip failure surface of specimen, and the bonding ratio Bn was calculated to analyze the effect of asphalt bonding on strength formation. Based on the deformation curve, the slip deformation behavior of asphalt mixture and the influence factors were analyzed from the microscopic perspective. Results obtained indicated that the optimum test conditions are the loading head of 28.5 mm, the diameter of the support ring of 80 mm, and the loading rate of 5 mm/min. The τsl was selected as the evaluation indicator of slip deformation behavior due to the best correlation with RD, good stability and sensitivity. The bonding effect of asphalt binder is greater than particle contact effect for suspended-dense asphalt mixture. The slip deformation of asphalt mixture can be divided into five stages, including densification, elastic deformation, viscoelastic deformation, initial cracking and plasticity slip deformation. The contact from coarse aggregates and bonding from asphalt binder can enhance the slip deformation resistibility. While the interference of fine particles and the lubrication of asphalt can accelerate the slip deformation of asphalt mixture.

Investigation on Indirect Tensile Test of Asphalt Mixture Based on the Discrete Element Method

Abstract The indirect tensile test is commonly used to evaluate crack and fatigue resistance of asphalt mixtures. However, laboratory tests are time-consuming and laborious in general. Numerical simulation provides a technical way for studying the mechanical behavior of asphalt mixtures. In this research, a laboratory test and discrete element method were used to explore the effects of temperature, air void content, loading rate, and the homogeneity of a mixture on the splitting strength of asphalt mixtures. For asphalt mixtures, a three-dimensional random modeling method and two-dimensional modeling method based on X-ray computed tomography and digital image processing were developed. Also, a homogeneity evaluation index based on ring segmentation was proposed. The results show that an increase in loading rate and decrease in temperature resulted in a significant increase in splitting strength. With an increase in voids, the splitting strength of an asphalt mixture decreased. The Pearson correlation coefficient indicates that there seems to be no clear connection between splitting strength and homogeneity, but there is a significant correlation between the homogeneity and differences in the splitting strength.

Acoustic emission propagation characteristics and damage source localization of asphalt mixtures

Fracture of asphalt materials has been a critical issue that affects the fatigue performance and service life of asphalt pavements. Acoustic emission (AE) technique, as a kind of non-destructive testing (NDT) method, can effectively detect minor damage in various materials. The objective of this paper was to propose a damage source localization method suitable for understanding the fracture behavior of asphalt mixtures by AE detection. Firstly, the pencil-lead-break (PLB) tests were conducted on asphalt mixture beams to explore the propagation characteristics of AE signals, and a reasonable layout scheme of AE sensors was determined for monitoring the AE process of asphalt mixtures. Secondly, the wavelet threshold denoising method was utilized to extract effective information from AE signals associated with the pencil-lead breaks on the surface of asphalt mixture beam by simultaneously considering the wavelet basis functions, decomposition levels and threshold rules. Finally, an effective time difference of arrival (TDOA) estimation method combining noise reduction, wavelet decomposition and cross-correlation processing was established to accurately locate the damage source of asphalt mixtures. The results show that there is less serious attenuation of amplitude and energy of AE parameters and frequency spectrum of AE waveforms within the range of 100 mm in asphalt mixtures. The larger signal-to-noise ratio (SNR) and the smaller root mean square error (RMSE) of denoised AE signals indicate that the threshold denoising method optimized by the Fruit Fly Optimization Algorithm (FOA) is more effective for AE detection of asphalt mixtures. The improved TDOA estimation method could obtain a minimum TDOA value, and the calculated locations of AE events are closer to the actual PLB points.

Study on interfacial debonding between bitumen and aggregate based on micromechanical damage model

ABSTRACT Macro-scale fractures of asphalt mixture usually exhibit multiple failure mechanisms including aggregate cracking, interfacial debonding between bitumen and aggregate, and binder tearing; however, damage modelling through conventional continuum mechanics fails to take into consideration the effects of the small-scale physical phenomena. This study aims to introduce a micromechanical damage model for a fundamental understanding of interfacial debonding in asphalt mixtures. The bilinear Cohesive Zone Model (CZM) was incorporated into the Mori-Tanaka model and the constitutive behaviour of asphalt mixtures was predicted. The results show that the interfacial debonding exhibit a significant dependency on aggregate size. A critical aggregate size was identified, above which the damage behaviour of asphalt mixtures changes from hardening to softening. The critical aggregate size increases withmortar modulus but decreases with softening interfacial stiffness, Poisson’s ratio of the mortar and aggregate volume fraction. The interface strength and the fracture energy also have a significant effect on the fracture behaviour of asphalt mixtures. The strength of asphalt mixtures increases as the interface strength increases; it is independent of the fracture energy. Increased fracture energy can improve the fracture resistance of the asphalt mixture, while increased interface strength has an opposite effect.