Conventional asphalt binder derived from the petroleum refining process is widely used in pavement engineering. However, asphalt binder is a non-renewable material. Therefore, the use of a co-production of renewable bio-oil as a modifier for petroleum asphalt has recently been getting more attention in the pavement field due to its renewability and its optimization for conventional petroleum-based asphalt binder. Significant research efforts have been done that mainly focus on the mechanical properties of bio-asphalt binder. However, there is still a lack of studies describing the effects of the co-production on performance of asphalt binders from a micro-scale perspective to better understand the fundamental modification mechanism. In this study, a reasonable molecular structure for the co-production of renewable bio-oils is created based on previous research findings and the observed functional groups from Fourier-transform infrared spectroscopy tests, which are fundamental and critical for establishing the molecular model of bio-asphalt binder with various biomaterials contents. Molecular simulation shows that the increase of biomaterial content causes the decrease of cohesion energy density, which can be related to the observed decrease of dynamic modulus. Additionally, a parameter of Flexibility Index is employed to characterize the ability of asphalt binder to resist deformation under oscillatory loading accurately.

Asphalt pavements are commonly used for highways and airport runways. In pavement design and analysis, environmental factors such as temperature need to be taken into account to accurately predict the service life of asphalt pavements. The effect of temperature variations on the mechanical performance of asphalt mixtures was investigated at the microscale in this study. X-ray computed tomography (X-ray CT) scanning and digital image processing (DIP) techniques were applied to detect, analyze, and reconstruct the microstructure of asphalt specimens. Based on DIP, indicators related to air voids before and after fatigue testing were obtained and are discussed in this study. The results show that higher test temperatures resulted in larger air voids and promote crack initiation. Asphalt specimens measured at higher temperatures exhibited more prominent cracking characteristics because of decreased bonding capability between asphalt mastic and aggregates and because of decreased strength of the asphalt mastic. Finite-element simulations were conducted to simulate uniaxial compression tests. With increasing temperature, the proportion of larger compressive maximum principal stresses at the interface between the asphalt mortar and the aggregates decreased. Energy dissipation decreased with increasing temperature. The results reveal the significant influence of temperature on the fatigue damage and mechanical responses of asphalt; further investigations should be carried out to facilitate the improvement of the pavement design process.

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.

In recent years, energy harvesting technologies have been applied in pavement engineering. Piezoelectric energy harvesting in pavement aims to take advantage of the vehicle load on a road. Most of the existing theoretical and experimental research focused on the materials, structures, and shape of the energy harvesters to improve the efficiency of the output energy. However, few investigations have analyzed the compatibility of piezoelectric energy harvesters (PEHs) and pavement. This study investigated the influence of PEHs on the structural response of asphalt pavement. Three-dimensional (3D) tire–pavement interaction finite-element models with and without a PEH were constructed according to a previous demonstration project. Several critical points within the pavement structures were selected and their mechanical responses induced by the passing tire were compared and discussed. A parametric study analyzed the pavement responses to different traffic speeds, tire loads, and bonding conditions between the PEHs and asphalt layers. Two potential optimization solutions for the PEH were explored. The results showed that the influence of the PEH on the asphalt pavement performance is significant in terms of the horizontal and vertical strains and von Mises stresses. A PEH causes potential permanent damage initiation in its adjacent area within the pavement structure. The maximum values of the horizontal tensile strains appeared at the bottom of the asphalt surface course in all pavement models with a PEH. These conclusions offer basic information for improving the practical design of PEHs in asphalt pavement.

The feasibility and effectivity of recycling waste rubber and waste plastic (WRP) into asphalt binder as a waste treatment approach has been documented. However, directly blending WRP with asphalt binder brings secondary environmental pollution. Recent research has shown that the addition of WRP into asphalt binder may potentially improve the workability of asphalt binder without significantly compromising its mechanical properties. This study evaluates the feasibility of using the additives derived from WRP as a multifunctional additive which improves both the workability and mechanical properties of asphalt binder. For this purpose, WRP-derived additives were prepared in laboratory. Then, three empirical characteristics—viscosity, rutting factor, fatigue life were analyzed. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were employed to evaluate the effect of WRP-derived additive on the workability and chemical and mechanical properties of base binder. The dispersity of WRP-derived additive inside asphalt binder was also characterized using fluorescence microscope (FM). Results from this study showed that adding WRP-derived additive increases the workability of base binder. The WRP-derived additive appears positive on the high- and low- temperature performance as well as the fatigue life of base binder. The distribution of the WRP-derived additive inside base binder was uniform. In addition, the modification mechanism of WRP-derived additive was also proposed in this paper.