Crack healing has been a key area of asphalt pavement research. In this review, different crack-healing theories and crack-healing evaluation methods in bitumen and asphalt mixtures are summarized and presented. Then different crack healing technologies have highlighted the problems and solutions associated with their implementation. Detailly, traditional technologies (hot pouring and fog seal) are introduced. They mainly fill cracks from the outside, which can effectively prevent further damage to the asphalt pavement, when the cracks have generally developed to the middle and late stages of practical engineering. Their extension of the life of the asphalt pavement is relatively limited. Energy supply technologies (induction and microwave heating) have demonstrated significant efficacy in enhancing the crack healing capability of asphalt pavement, particularly in microcracks. Now, Extensive laboratory testing and some field test sections have been conducted and they are waiting for the promotion from the industry. The agents encapsulated technologies (Saturated porous aggregates encapsulate rejuvenators, Core-shell polymeric microcapsules, Ca-alginate capsule, Hollow fibers and Compartment fibers) not only heal cracks but rejuvenate the aged asphalt pavement. In order to promote industrial application, more field test sections and large industrial mixing and compaction equipment applications need to be implemented. Finally, some other potential crack healing techniques (coupling application, electrical conductivity, 3D printing, and modifications) are also mentioned.

To develop a mechanistic-empirical pavement design system for Norwegian conditions, this paper evaluates the influence of the adoption of different models and shifting techniques on the determination of dynamic modulus master curves of asphalt mixtures. Two asphalt mixture types commonly used in Norway, namely Asphalt Concrete (AC) and Stone Mastic Asphalt (SMA) containing neat bitumen and polymer-modified bitumen, were prepared by the roller compactor, and their dynamic moduli were determined by the cyclic indirect tensile test. The dynamic modulus master curves were constructed using the standard logistic sigmoidal model, a generalized logistic sigmoidal model and the Christensen–Anderson–Marasteanu model. The shifting techniques consisted of log-linear, quadratic polynomial function, Arrhenius, William–Landel–Ferry and Kaelble methods. The absolute error, normalised square error and goodness-of-fit statistics encompassing standard error ratio and coefficient of determination were used to appraise the models and shifting methods. The results showed that the standard logistic sigmoidal model and the Williams–Landel–Ferry equation had the most suitable fits for the specimens tested. The asphalt mixtures containing neat bitumen had a better fit than the ones containing polymer-modified bitumen. The Kaelble equation and log-linear equation led to similar results. These findings provide a relevant recommendation for the mechanistic-empirical pavement design system.

The aging of bitumen is detrimental to the durability and service life of asphalt pavement. Previous studies found that bitumen was suspected to be aged by not only thermal oxidation but also solution immersion. This research aims to compare the effect of thermal-oxidative aging and salt solution aging on bitumen performance. For this purpose, a thin film oven test (TFOT) and pressure aging vessel aging (PAV) were selected as thermal-oxidative aging, and 10% NaCl aging and 10% CaCl₂ aging were selected as salt solution aging. The morphology, oxygen content, physical properties, low-temperature properties, and high-temperature properties of bitumen were analysed by employing scanning electron microscopy with an energy dispersive spectrometer (SEM-EDS), physical tests, a bending beam rheometer (BBR), and a dynamic shear rheometer (DSR). Test results show that both thermal-oxidative aging and salt solution aging had similar influencing trends in the oxygen content, physical, low-temperature, and high-temperature properties of bitumen but had different changes in morphology. The aging degrees caused by four kinds of aging methods were obtained based on the summed values of the absolute aging factor of all parameters: PAV > 10% NaCl > TFOT > 10% CaCl₂. The conclusions could provide a theoretical basis to establish a standard for the solution aging of bitumen.

The beneficial effects of applying microwave energy in asphalt pavements maintenance are receiving increasing attention recently, while its aging impact remains less explored. This study aims to investigate the microwave aging impact on asphalt binders. Different microwave heating cycles are applied on steel slag asphalt mixtures, and the aging effect on extracted asphalt binders, including the physical, rheological properties and infrared spectra, are evaluated with penetration and softening point tests, Dynamic Shear Rheometer (DSR), and Fourier Transform Infrared (FTIR) spectroscopy. Results indicate that the aging issue occurs on asphalt binder after the application of MH treatment. A relatively apparent deterioration can be observed in the physical and rheological properties during the first 10 MH cycles, and minor changes can be further detected during the later cycles. In addition, the microwave radiation also exerts changes in asphalt components, i.e. sulfoxide groups, while the changes in carbonyl groups are not significant.