Engineering performance of asphalt pavement highly depends on the properties of bitumen, the bonding material to glue aggregates and fillers together. During the service period, bitumen is exposed to sunlight, oxygen and vehicle loading which in turn leads to aging and degradation. A comprehensive understanding of the aging mechanism of bitumen is of critical importance to enhance the durability of asphalt pavement. This study aims to determine the relations between micro-mechanics, chemical composition, and macro-mechanical behavior of aged bitumen. To this end, the effect of aging on micro-mechanics, chemical functional groups, and rheological properties of bitumen were evaluated by atomic force microscope, Fourier transform infrared spectroscopy and dynamic shear rheometer tests, respectively. Results indicated that aging obviously increased the micro-surface roughness of bitumen. A more discrete distribution of micromechanics on bitumen micro-surface was noticed and its elastic behavior became more significant. Aging also resulted in raised content of carbonyl, sulfoxide, and aromatic ring functional groups. In terms of rheological behavior, the storage modulus of bitumen apparently increased after aging due to the transformation of viscous fractions to elastic fractions, making it stiffer and less viscous. By correlation analysis, it is noted that the bitumen rheological behavior was closely related to its micro-mechanics.

Asphalt rubber (AR) is a sustainable paving material with merits including waste tire consumption, low traffic noise, and enhanced mechanical performance. However, the poor workability and storage stability limited its further application. This study attempted to alleviate these two concerns of AR simultaneously by incorporating heavy bio oil (HBO). To achieve this goal, bio-AR binders with three different mixing sequences were prepared. A series of rheological and chemical tests were conducted. Test results prove that the bio-AR binders exhibited superior rutting and fatigue resistance compared to AR binder. The viscosity values of bio-ARs were closed to AR modified with commercial warm mix additive, which indicates enhancement in workability. Due to the relatively high density of HBO, the density difference between the asphalt liquid phase and crumb rubber in the bio-AR system narrowed, which brought improved storage stability. Among bio-ARs prepared with different mixing sequences, the direct mixing one (ARB) had the most satisfied overall performance. The early incorporation of HBO had limited negative influence on binder performance, but allowed for more energy saving during the bio-AR binder production. Future study will be conducted on performance of bio-AR mixtures and quantitative estimation of its energy saving during the blending and compacting process.

Gradation segregation strongly affects the service performance of asphalt pavement. However, rare studies focus on the influences of segregation on asphalt mixture as it is difficult to simulate segregation in a laboratory. This paper presents a research aiming to evaluate the effects of gradation segregation using the two dimensional (2D) discrete element method (DEM). To achieve this objective, the gradation segregation levels are defined according to the differences between control and segregated gradations. Based on this, asphalt mixtures with three gradations at three segregation levels were selected. The corresponding 2D DEM models were then built using Particle Flow Code 2D (PFC 2D). The aggregate skeletons in the asphalt mixture were determined separately by means of the contact point and contact force. Based on this, the variations on the aggregate skeleton, aggregate distribution, and mechanical properties of the asphalt mixture under vertical load were studied at three different segregation levels. This study indicates that the aggregate skeleton in asphalt mixture can be affected by the gradation segregation. The correlation between gradation segregation and mechanical property is also determined in this study.

The purpose of this study is to discuss the impact of social responsibility on the company's value. Taking Xiaomi Company as a case, the research objects are decision-making level, management level and grass-roots employees by questionnaire survey. The sampling method is purposive sampling. 125 groups of samples (decision-making level and management level) and 623 groups of samples (grass-roots employees) are sampled. Hierarchical model (HLM) and hierarchical regression are used to analyze the positive impact of different levels of employees on social responsibility on the company's value and verify it.

Experimental strain testing of composite shells under 15MPa hydrostatic pressure was conducted using both strain gauges and underwater 3D-DIC (Digital Image Correlation) testing technology. The experimental results showed a large error in the measurement results of strain gauges when small-sized components were present in the test area of the experimental object. The average standard deviation of the strain results was 716.1 με and the average standard deviation of the Mises stress results was 120.9 MPa. However, the strain results of the underwater 3D-DIC test system in the circumferential direction of the composite shell were generally consistent. This proves that the system can maintain good test accuracy even under high hydrostatic pressure environments.