Three-dimensional ground penetrating radar (3D GPR) is a non-destructive examination technology for pavement distress detection, for which its horizontal plane images provide a unique perspective for the task. However, a 3D GPR collects thousands of horizontal plane images per kilometer of the investigated pavement. The existing detection methods using GPR images are time-consuming and risky for subjective judgment. To solve the problem, this study used deep learning methods and 3D GPR horizontal plane images to detect pavement structural distress, including cracks, repairs, voids, poor interlayer bonding, and mixture segregation. In this study, two deep learning methods, called CP-YOLOX and SViT, were used to achieve the aim. A dataset for anomalous waveform localization (3688 images) was first created by pre-processing 3D-GPR horizontal plane images. A CP-YOLOX model was then trained to localize anomalous waveforms. Five SViT models with different numbers of encoders were adopted to perform the classification of anomalous waveforms using the localization results from the CP-YOLOX model. The numerical experiment results showed that 3D GPR horizontal plane images have the potential to be an assistant for pavement structural distress detection. The CP-YOLOX model achieved 87.71% precision, 80.64% mAP, and 33.57 sheets/s detection speed in locating anomalous waveforms. The optimal SViT achieved 63.63%, 68.12%, and 75.57% classification accuracies for the 5-category, 4-category, and 3-category datasets, respectively. The proposed models outperformed other deep learning methods on distress detection using 3D GPR horizontal plane images. In the future, more radar images should be collected to improve the accuracy of SViT.

When using a high concentration of reclaimed asphalt pavement (RAP) in a recycled hot-mix asphalt mixture (RHMA), the degree of blending of the reclaimed asphalt binder significantly affects the performance of the RHMA. Hence, it is essential to know the degree of blending of the RAP and its effect on the performance and the environmental impact of RHMA in order to determine the optimal mixing duration. To this end, the dispersion of reclaimed asphalt was observed using artificial RAP and the image analysis method, and the blending of reclaimed asphalt in RHMA with different mixing durations was also evaluated using physical properties tests, a rheometer test, a Fourier-transform infrared spectroscopy (FTIR) test, a gel permeation chromatography (GPC) test, and an atomic force microscope (AFM) test. The performance of RHMA with the different mixing durations in the plant and in the laboratory was tested using a Marshall stability test, rutting resistance test, freeze–thaw splitting test, and low-temperature bending beam test. In addition, the environmental impact of RHMA at different mixing durations was evaluated, and the optimal mixing duration was determined. The results showed that the mixing duration had a significant influence on the dispersion and blending of reclaimed asphalt in RHMA. The longer the mixing duration was, the higher the dispersion and the degree of blending of the reclaimed asphalt in the RHMA were. With the increase in the mixing duration, the properties, chemical composition, and micromorphology of the blended asphalt binder tended to become similar to those of reclaimed asphalt. The performance of RHMA was improved with the increase in mixing duration; however, the energy consumption and CO₂ emissions for the RHMA increase significantly with the increase in mixing time. The recommended optimal mixing durations in the mixing plant and in the laboratory were found to be 60 s and 90 s, respectively, considering the environmental impact, the RHMA production efficiency, and the performance of the RHMA.

To investigate the feasibility of composite modification techniques in improving the performance of recycled asphalt mixtures, in this study, the high-viscosity agent (HVA) and crumb-rubber materials (CRM) were used to modify asphalt with a styrene-butadiene-styrene block copolymer (SBS), in order to prepare SBS-HVA and SBS-CRM composite-modified asphalts. The virgin asphalt mixtures, as well as three asphalt types of recycled asphalt mixtures with 50% reclaimed asphalt pavement (RAP) content, were designed. The optimal asphalt content of the four types of asphalt mixtures was analyzed, and the rutting test, the asphalt bond strength test, the moisture-induced sensitivity test, and the low-temperature cracking resistance test were conducted to investigate the performance of the four types of asphalt mixtures. The results showed that the higher the asphalt kinematic viscosity, the higher the optimum asphalt content of the asphalt mixtures under the same air voids. HVA significantly improves the adhesion between SBS-modified asphalt and aggregate under dry conditions, while SBS-CRM composite-modified asphalt performs similarly to SBS-modified asphalt. Before and after water immersion, the degree of pull-out strength decay between the asphalts and aggregates follows the sequence of SBS-CRM- > SBS- > SBS-HVA-modified asphalts. Additionally, the residual pull-out work follows the sequence of SBS-HVA- > SBS-CRM- > SBS-modified asphalt. SBS-CRM composite-modified asphalt can significantly improve the moisture sensitivity of recycled asphalt mixtures, as well as low-temperature cracking resistance, while SBS-CRM composite-modified asphalt only improves the low-temperature cracking resistance of recycled asphalt mixtures, and does not improve the moisture sensitivity. Based on the results, it is recommended to select the appropriate composite modification method based on the climate and loading conditions, to maximize the value of asphalt, and to achieve sustainable and durable pavement.

This paper selected three kinds of AC-20 hot-mix recycled asphalt mixtures with high RAP content (30%, 40%, and 50%). It obtains a mixture of different degrees of miscibility by changing RAP preheating temperatures and mixing temperatures. The calculation formula of the degree of blending (DOB) of RAP asphalt interface recycling is proposed. The DSR test quantitatively characterized the DOB mixture’s low temperature, and fatigue properties were tested by beam bending test and four-point bending fatigue test. The prediction models of the recycled mixture’s low temperature and fatigue properties were proposed. The RAP preheating temperature is the most critical factor that dominates both transfers of RAP asphalt to the surface of new aggregate and the effective blending of old and new asphalt. DOB has a significant great influence on low-temperature performance and fatigue performance. The DOB of recycled asphalt can be improved by adjusting and optimizing the process parameters of plant hot recycled mixture to effectively improve the recycled mixture’s low-temperature crack resistance and fatigue lifetime. The optimal RAP dosage and mixing process of required performance can be obtained based on the prediction models to save experimental time and cost.

Aiming at the problems of asphalt pavement crack sealing and pothole repair materials, an epoxy- resin adhesive with high forming strength, good toughness and room-temperature curing was prepared. In addition to being used as a road filling sealant, the adhesive can also be used for preparing a cold patching mixture for pits. The properties of the epoxy-resin adhesive, the construction performance and road performance of the pouring sealant and cold patch were studied. The results showed that the early strength of the epoxy-resin adhesive was fast and high, the curing volume shrinkage was small, the low-temperature characteristics and tensile properties were good, and the toughness was excellent. As a pouring sealant, the epoxy-resin adhesive had excellent low- temperature bending resistance. The cold patching mixture based on the adhesive exhibited strong cohesiveness, good low-temperature crack resistance, and excellent high-temperature stability and water stability. This adhesive expands the application of epoxy resin in repairing cracks and pits of asphalt pavements, and is of great significance in promoting the development of the asphalt pavement maintenance technology.