Minrui Guo

Studies on triaxial contact stresses and asphalt pavement rutting are of great significance for traffic safety and the durability of the asphalt pavement. Our new approach considers more evaluating indicators by investigating compressive creep, vertical, and longitudinal permanent deformation to analyse asphalt pavement rutting under triaxial contact stress during typical driving conditions. For this purpose, firstly sophisticated three-dimensional finite element models encompassing the truck-bus tire and asphalt pavement temperature are developed. Secondly, a comparative analysis was conducted by collating the predicted deformations obtained through finite element analysis with the deformations measured in laboratory experiments using specialized sensors. Finally, the rutting analysis process under triaxial contact stresses during typical driving conditions is established. The results show asphalt pavement exhibits different temperature gradient changes between daytime and nighttime during the summer season. The longitudinal contact stress under braking condition has a significant impact on the longitudinal permanent deformation and compressive creep of asphalt pavement, especially, the longitudinal permanent deformation of the feature points in the middle layer exhibits the most pronounced sensitivity to this contact stress. In addition, the maximal compressive creep is observed at the top of the middle layer, although the characteristic positions for the maximum values of positive and negative creep differ. The proposed new method is beneficial for improving the accuracy and comprehensiveness of asphalt pavement rutting analysis.

The primary purpose of the research is to explore triaxial contact stresses of the green bus tire including complex rubber materials and rim. An accurate finite element model of the bus tire is constructed using ABAQUS software after verification. The measured and calculated values have good consistency under different tire loads and inflation pressures. The finite element model is applied for quantitative research by changing tire loads, inflation pressures, and rolling conditions. The analysis results show that higher inflation pressure increases vertical contact stress, which requires a reasonable balance between high load and high inflation pressure. When the inflation pressure increases, the position of the maximum longitudinal contact stress shifts forward, and the maximum transverse contact stress shifts inboard in the transverse direction. When the tire load becomes larger at the free rolling condition, the position of the maximum vertical contact stress moves forward, and the position at the full braking condition is more advanced under the same load conditions. Overload not only causes great damage to the tire during the braking condition but also accelerates the appearance of the rutting and shoving of the road.

The primary purpose of the research is to explore the combined effects of the tire loading velocity (LV) and the nonlinear cross-anisotropic properties of granular base on critical pavement responses. An accurate finite element (FE) model of the pavement structure is constructed using ABAQUS software after verification. The FE model is applied for quantitative research by changing the nonlinear cross-anisotropic characteristic parameters under different LVs, which is done to determine the relationship between the critical strain responses and LVs under nonlinear cross-anisotropic properties. The transverse tensile strain is found to be exerted on the pavement for a longer amount of time than the longitudinal tensile strain. It also found that the critical longitudinal, transverse, and shear strains can be described as having exponential relationships. The exponent coefficients indicate that the influences of the LV on these three types of strains are analogical. In other words, with the increase of tire velocity, the critical strains decay exponentially. The LV is found to have a limited impact on the compressive strain under the same nonlinear cross-anisotropic properties. However, the effects of nonlinear cross-anisotropic properties on the compressive strain at the top of the subgrade are obvious.

In this work, to analyse the changing characteristics of contact stresses in the tyre–pavement interface and the functional relationship between rolling resistance and the working conditions of truck-bus tyres, a three-dimensional tyre–pavement model is established and used to predict the distribution of contact stresses and rolling resistance under different working conditions of the tyre, comprising various tyre loads, inflation pressures, and velocities. Results show that the magnitude relationship between transverse and longitudinal contact stresses is related to rolling conditions, and overload and low tyre pressure are important contributors to the wear of the tyre shoulder. In addition, the proposed exponential equation presents a method that can be used to forecast rolling resistance related to the working conditions of the truck-bus tyre, and a similar method can be used to predict the rolling resistances of other types of tyres.

Based on attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy and principal component analysis (PCA), four kinds of asphalt (two kinds of matrix asphalts, TPC70# and JL70# and two kinds of modified asphalts, SBS-1 and SBS-2) were aged using the rolling thin-film oven test (RTFOT). The multiple stress repeated creep recovery test (MSCR) was carried out on an AR1500ex dynamic shear rheometer (DSR). The PCA was carried out on the attenuated total reflection infrared spectrum of a pretreated aged asphalt, the principal component factors (oxidation factor and component change factor) were determined, the comprehensive index F was calculated, and a prediction model of aging time history was established and verified. A prediction model for the aging asphalt recovery rate R was established based on the functional group index. The relationship between the recovery rate R and aging time history of each aging asphalt was analyzed and the fatigue life of each aging asphalt based on the rate of dissipated energy change (RDEC) was compared. The correlation between the comprehensive index F and fatigue life of asphalt was also analyzed. The results show that the order of resistance to the high-temperature deformation of each aging asphalt is as follows: SBS-2 > SBS-1 > TPC70# > JL70#; the prediction model of aging asphalt recovery rate R based on functional group index has good reliability. Taking the loading cycle corresponding to the sudden increase of the inflection point of the curve, i.e., the fatigue life N_RDEC, as the evaluation index, the fatigue life order of each aging asphalt is SBS-1 > SBS-2 > JL70# > TPC70#. There is a positive correlation between the fatigue life of aged asphalt and the comprehensive index F of asphalt. The correlation degree R² is 0.85; i.e., with the increase of the comprehensive index F of asphalt, its fatigue life also increases. It was found that it is feasible to analyze the aging time history and fatigue life of asphalt by infrared spectroscopy, and it can provide a rapid and non-destructive prediction method for the practical engineering application of asphalt.

The contact stress distribution of tire-pavement is generally assumed to be uniformly distributed in circles or rectangles in the pavement design. This simplification can solve some common engineering problems, but it neglects two factors including magnitude and direction of the contact stress. The main purpose of this paper is to analyze the contact stress distribution between the bus tire and the pavement under different driving conditions and pinpoint and compare the critical slip ratio during braking and acceleration. First, a tire-pavement simulated contact model is constructed by ABAQUS. Next, we compare, respectively, contact stresses in the vertical, longitudinal, and transverse directions at various rolling conditions and analyze the longitudinal forces at different slip ratios during braking and acceleration. It is observed that the magnitude, direction, and nonuniform distribution of contact stress are affected by the multiple working conditions while the bus is working. Meanwhile, in the braking and acceleration conditions, the longitudinal force grows rapidly as the slip ratio increases, and then grows slowly and at last decreases when the critical slip ratio is reached. However, the critical slip ratio at the time of braking differs from that at the time of acceleration, and the former is smaller than the latter.