Jun Xie

To investigate coarse aggregate migration on mesoscale rutting deformation of asphalt mixtures, AC‐13 and AC‐20 were selected. Sandblasting and iron powder tracing were combined with the Hamburg wheel tracking test and industrial CT scanning to obtain cross‐sectional images during rutting failure. Digital image processing (DIP; noise reduction, edge detection, threshold segmentation) was applied, and aggregate movement parameters were extracted using Matlab and Image‐Pro Plus. Based on the CT images, a three‐dimensional structural model was built in Avizo and then imported into PFC3D for discrete element (DEM) simulations, which serve to reproduce and explain the experimentally observed aggregate movements. Results show that after rutting, AC‐20 coarse aggregates had a higher average displacement (3.154 mm vs. 2.356 mm) and greater dispersion than AC‐13. Displacement increased with loading cycles, most notably in the upper‐middle layer (15%–30% thickness), reaching a maximum of 6.96 mm. Average coordination numbers increased (AC‐13: 3.01→5.14; AC‐20: 2.61→4.94), indicating more contacts and a denser structure; void ratio decreased, confirming further compaction. DEM simulations further revealed that vertical displacement (1–6 mm) was much larger than horizontal displacement (<2 mm) and increased with height; smaller aggregates showed more pronounced vertical movement. By linking CT observations with DEM simulations, this study elucidates the mesoscale evolution mechanisms of different gradations under loading, providing a mechanistic explanation for rutting deformation and guidance for gradation optimization and rutting resistance improvement.

The dynamic load caused by vehicle vibration due to an uneven pavement surface is a primary factor affecting the structural performance and service life of asphalt pavement. As the principles of vibration mechanics, in conjunction with the coherence function of the vehicle’s left and right wheels, along with the lag between front and rear wheels, the entire vehicle vibration model for three-axle and four-axle heavy-load vehicles was developed using Simulink software. Through simulation, the root-mean-square value of the dynamic load and the dynamic load coefficient of the vehicle with different pavement roughness grades, speeds, loads, and cornering radii were analyzed. The outcomes demonstrate that a nonlinear rise in the wheel dynamic load occurs when pavement roughness increases. The greater the speed, the greater the impact of pavement roughness on the dynamic load. An increase in vehicle load tends to reduce vehicle vibrations. The interaction between vehicle vibration frequency and road excitation frequency is essential in figuring out the loads, and a negative influence on the pavement structure should be given more attention when the vehicle is driving at low speed. The dynamic load coefficient of the left and right wheels is greatly affected when the vehicle is in a lateral tilt. The findings offer valuable insights for selecting appropriate loads in pavement structure design. By constructing 11 degrees of freedom for a three-axle vehicle and 16 degrees of freedom for a four-axle heavy-duty vehicle model, the dynamic load variation law under different roughness excitation conditions is systematically analyzed. The results can be applied to the selection of vehicle load in asphalt pavement design to make it closer to the actual driving state, which will be helpful for improving accuracy in the design of pavement structure and avoiding early damage to the pavement.

In pavement design, vehicle load is typically simplified as vertical circular uniform loading. Due to the vehicle dynamic effect and deformation of a tire, non-uniform three-dimensional contact stresses are produced at the contact interface between the tire and pavement under different driving modes. For this paper, an 11R22.5 truck radial tire was selected. Considering the geometric nonlinearity and large deformation of the tire and nonlinear characteristics of tire-pavement contact, the Neo-Hookean and Rebar models are used to simulate the hyperelastic rubber material and rubber-cord composite material, respectively. The three-dimensional contact stress distribution under static, free rolling, acceleration, braking, and cornering modes was simulated and analyzed. The results show that inflation pressure, axle load, and friction coefficient of the tire significantly affect the three-dimensional contact stress distribution. Further, three-dimensional stresses are non-uniformly distributed, rather than in the traditional simplified circular uniform load. The three-dimensional stress distribution of tire-pavement in different driving modes is also significantly different. The vertical and lateral stresses in the state of cornering are the largest, the longitudinal stress in the state of braking is the largest as well. The research results provide reference for future pavement design and pavement damage analysis.

In order to address the influence of aging on the performance degradation of SBS‐modified asphalt, a composite modification of SBS‐modified asphalt by nano‐zinc oxide (nano‐ZnO) and Trinidad Lake asphalt (TLA) was proposed. Several tests were conducted after adding nano‐ZnO and TLA to SBS‐modified asphalt, including a rotary film oven test (RTFOT), ultraviolet aging (UV), and the pressure aging vessel test (PAV). The conventional physical index, rheological index, and four‐component content of SBS‐modified asphalt before and after three aging modes were tested, and the characteristic functional groups in SBS‐modified asphalt were tracked and analyzed by Fourier transform infrared spectroscopy (FTIR). The results show that the effects of aging on the rheological properties of SBS‐modified asphalt are clearly reduced by adding different proportions of nano‐ZnO and TLA in the process of thermal oxygen aging and the ultraviolet aging test, and the antiaging ability of SBS‐modified asphalt is clearly improved. To improve the conventional performance and rheological properties of SBS‐modified asphalt, an incorporation ratio of 3% nano‐ZnO + 25% TLA was proposed. At the same time, the increased rate of heavy components and the change index of the colloidal instability index in the SBS‐modified asphalt under the blending ratio were significantly lower than the blank SBS‐modified asphalt samples in the same aging mode. FTIR spectra also showed that SBS‐modified asphalt performance deterioration were mainly caused by long‐term aging and ultraviolet aging. The addition of nano‐ZnO and TLA effectively reduced the increase of carbonyl groups and the breakage of the C=C double bond in butadiene and synergistically improved the comprehensive aging resistance of SBS‐modified asphalt. Therefore, the use of this modification is an effective method to solve the aging problem of SBS‐modified asphalt.

In order to analyze the torsional shear process of asphalt mixtures in a microscopic view, the numerical simulation of a torsional shear test of an asphalt mixture was carried out by discrete element method. Based on the defects of existing algorithms, the method of random reconstruction of the existing 3D model of the asphalt mixture was improved, and a new reconstruction method was proposed. A 3D numerical model of the asphalt mixture contained irregular-shaped coarse aggregate, mineral gradation, and asphalt mortar; furthermore, the particle algorithm established the air void distribution. Then, the numerical simulation of the asphalt mixture’s torsional shear was completed; in addition, the stress, displacement, and contact of the specimens at each stage were analyzed. The results showed that the stress and displacement in different stages changed greatly with the loading, i.e., the crack generated from a weak point on the surface and then spread to the ends with an oblique angle of about 45°. At the same time, the shear failure process of the asphalt mixture was studied. The virtual test method could accomplish the implementation of the numerical simulation of torsional shear; it also provided a good research method for analysis of the asphalt mixture’s shear failure process.

Insufficient shear performance in an asphalt mixture is a primary reason for rutting deformation and pavement surface longitudinal cracking. Thus, it is important to choose a suitable shear test method to evaluate shear performance in an asphalt mixture. Current testing methods mainly evaluate the bonding strength between asphalt layers, and the current shear test method for an asphalt mixture is disadvantaged by high equipment cost and complicated procedures. Our study proposes a torsional test method under normal stress condition, and evaluation was done for four types of asphalt mixture under different temperature conditions. Through the mechanical analysis, the calculation formulas for shear strength and shear parameters (cohesion and internal friction angle) for the torsional test under a normal stress condition were obtained. Testing results were also obtained for shear strength, shear modulus, and cohesion and internal friction angle of the asphalt mixtures. Experimental testing indicated that the method was able to provide repeatable results for the shear resistance of asphalt mixtures at different temperatures and also reflected the difference in shear performance of the various asphalt mixtures and the influence of temperature on shear performance. The failure mode of the specimen was the appearance of an oblique crack of about 45° from the vertical axis after the specimen was destroyed, which accorded with shear failure characteristics. A shear fatigue model was obtained considering different shear stress levels. The torsional test method under normal stress formed a compression‐shear action on the specimen by applying torque and normal stress and was used to evaluate the shear performance of the asphalt mixtures.

In order to verify the reliability and effectiveness of the torsional shear test method, a comparative study of the torsional test under normal stress conditions and triaxial test was carried out with two different asphalt types (unmodified asphalt and SBS‐modified asphalt) for asphalt mixtures of AC‐13 and AC‐20 at three temperatures of 20°C, 40°C, and 60°C. The results showed that the crack spreading routine and the spreading angle were different between the two test methods. The cohesion of the torsional test was slightly larger than that of the triaxial test for different mixtures, asphalts, and temperatures. The main cause of this result is the difference of loading mode. The internal friction angle was basically equivalent in the two methods for different mixtures, asphalts, and temperatures, which indicated that the internal friction angle was mainly related to the spatial distribution of the aggregates or the mutual interlock and had little to do with the test method and external conditions. The results of the ANOVA and regression analysis indicated that the two test methods have a good correlation, and the torsional shear test is a reliable and effective laboratory test method for evaluating the shear performance of asphalt mixtures.

A growing body of evidence showed that flow rutting and inter-layer slippage in asphalt pavements at intersections and large longitudinal slopes is directly related to the capacity of the asphalt mixture to resist shear flow deformation. This study used fractal theory to analyze the microstructures of asphalt mixtures AC-13, SMA-13, and Sup-13, the volume fractal dimensions of which are also determined. The relation between the volume fractal dimensions and shear properties of asphalt mixtures was determined through repeated load creep tests.