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.

Microwave heating is an encouraging heating technology for the maintenance, recycling, and deicing of asphalt pavement. To investigate the microwave heating properties of asphalt mixture, laboratory tests and numerical simulations were done and compared. Two types of Stone Mastic Asphalt (SMA) mixture samples (with basalt aggregates and steel slag aggregates) were heated using a microwave oven for different times. Numerical simulation models of microwave heating of asphalt mixture were developed with finite element software COMSOL Multiphysics. The main thermal and electromagnetic properties of asphalt mixture, served as the model input parameters, were measured through a series of laboratory tests. Both laboratory-measured and numerical simulated surface temperatures were recorded and analyzed. Results show that the replacement of basalt aggregates with steel slag aggregates can significantly increase the microwave heating efficiency of asphalt mixture. Numerical simulation results have a good correlation with laboratory test results. It is feasible to use the developed model coupling electromagnetic waves with heat transfer to simulate the microwave heating process of asphalt mixture.

Pyrolytic carbon black (CB_p) from scrap tire pyrolysis is a potential modifier for the bitumen industry. Binders containing different contents of CB_p were prepared and experimentally investigated to examine the effects of CB_p on the electrical and thermal conductivity, conventional physical properties, rheological properties, high-temperature antirutting performance, aging resistance, and storage stability. Laboratory test results indicated that the incorporation of CB_p effectively improves the electrothermal properties, rheological properties, high-temperature rutting resistance, and aging resistance. It also increases the viscosity and decreases the storage stability of bitumen. The study confirms that CB_p-modified bitumen with proper selection of content can be a multifunctional paving material.

To give engineers involved in planning and designing of asphalt pavements a more accurate prediction of crack initiation and propagation, theory-based models need to be developed to connect the loading conditions and fracture mechanisms present in laboratory tests and under traffic loading. The aim of this study is to develop a technical basis for the simulation of fracture behavior of asphalt pavements. The cohesive zone model (CZM) approach was applied in the commercial FE software ABAQUS to analyze crack propagation in asphalt layers. The CZM developed from the asphalt mixtures in this study can be used to simulate the fracture behavior of pavements and further optimize both the structure and the materials. The investigations demonstrated that the remaining service life of asphalt pavements under cyclic load after the initial onset of macro-cracks can be predicted. The developed CZM can, therefore, usefully supplement conventional design methods by improving the accuracy of the predicted stress states and by increasing the quality, efficiency, and safety of mechanical design methods by using this more realistic modeling approach.

As a closed space, the functional requirements of the tunnel pavement are very different from ordinary pavements. In recent years, with the increase of requirements for tunnel pavement safety, comfort and environmental friendliness, asphalt pavement has become more and more widely used in long tunnels, due to its low noise, low dust, easy maintenance, and good comfort. However, conventional tunnel asphalt pavements cause significant safety and environmental concerns. The innovative polyurethane thin overlay (PTO) has been developed for the maintenance of existing roads and constructing new roads. Based on the previous study, the concept of PTO may be a feasible and effective way to enrich the innovative functions of tunnel pavement. In this paper, the research aims to evaluate the functional properties of PTO, such as noise reduction, solar reflection and especially combustion properties. Conventional asphalt (Open-graded Friction Course (OGFC) and Stone Mastic Asphalt (SMA)) and concrete pavement materials were used as control materials. Compared with conventional tunnel pavement materials, significant improvements were observed in functional properties and environmental performance. Therefore, this innovative wearing layer can potentially provide pavements with new eco-friendly functions. This study provides a comprehensive analysis of these environmentally friendly materials, paving the way for the possible application in tunnels, as well as some other fields, such as race tracks in stadiums.

The significance of water flow behavior as one of the main properties of pervious pavements has long been recognized. However, the quantification of flow characteristics and the relationship to complex pore microstructures in pervious pavement remains incomplete. The aim of current research is to quantify the Darcy and non-Darcy flow in pervious pavement materials and carry out investigations on the different flow models for predicting hydraulic conductivity. Conventional porous asphalt (PA) and an innovative polyurethane-bound pervious mixture (PUPM) were adopted for comparative study in this research. A custom-made permeameter was used to analyze the water flow characteristics in pervious pavement mixtures subjected to different hydraulic gradients. The results illustrate the inapplicability of Darcy’s law in the analysis of directional moisture transport in pervious pavement materials. In particular, the Reynolds number of pervious pavement materials increases with the hydraulic gradient, indicating that the flow in pervious pavement material transits from Darcy flow to Forchheimer flow. The pore microstructure of the pavement material is quantified using X-ray computed tomography (CT) images. ANOVA indicates that it is mainly the pore distribution characteristics, including air void content, void diameter, and tortuosity, that influence the flow in pervious pavement. Modified flow models are developed based on the pore microstructures, which present better consistency with the experimental results. The developed experiments and models can provide a firm foundation for the optimization of pervious pavement design in engineering applications.