In order to solve the problems caused by asphalt diseases and prolong the life cycle of asphalt pavement, many studies on the properties of modified asphalt have been conducted, especially polyurethane (PU) modified asphalt. This study is to replace part of the styrene-butadiene-styrene (SBS) modifier with waste polyurethane (WP), for preparing WP/SBS composite modified asphalt, as well as exploring its properties and microstructure. On this basis, this paper studied the basic performance of WP/SBS composite modified asphalt with a conventional performance test, to analyze the high- and low-temperature rheological properties, permanent deformation resistance and storage stability of WP/SBS composite modified asphalt by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The microstructure of WP/SBS composite modified asphalt was also observed by fluorescence microscope (FM) and Fourier transform infrared spectroscopy (FTIR), as well as the reaction between WP and asphalt. According to the results of this study, WP can replace SBS as a modifier to prepare WP/SBS composite modified asphalt with good low-temperature resistance, whose high-temperature performance will be lower than that of SBS modified asphalt. After comprehensive consideration, 4% SBS content and 15% WPU content (4 S/15 W) are determined as the suitable types of WPU/SBS composite modified asphalt.

The realization of nondestructive detection and classification of pavement distress is of great significance for putting forward a reasonable maintenance scheme and prolonging the service life of the road. In this paper, the advanced air-coupled 3D ground-penetrating radar (3D-GPR) was used to detect Li-Ma Expressway (Jiangsu Province, China) to achieve the purpose of rapid, accurate, and nondestructive testing. Through on-site coring at the corresponding radar anomaly signal, it is verified that the 3D-GPR can identify the characteristics of pavement distress. To address the issue of a large amount of 3D-GPR images required to be processed and low efficiency of current manual classification, VGG16 and ResNet50 models were established based on deep convolutional neural network to classify four pavement distresses automatically. The results showed that the maximum accuracy, precision, and recall obtained from the VGG16 model training results were 98.73%, 97.98%, and 96.17%, respectively. In addition, The overall processing time of VGG16 to identify 2525 radar images with $200$ $\times$ $ 200$ pixels is 232 s. And VGG16 was selected as the automatic classification model of 3D-GPR image for pavement distress of Li-Ma Expressway.

The use of rejuvenators has enhanced the workability of asphalt mixtures containing the reclaimed asphalt pavement (RAP). This conclusion is based on the determination of viscosity of asphalt binders, while not validated from reclaimed asphalt mixtures. In this study, the effect of two rejuvenators (ordinary and emulsified rejuvenator) on the workability of reclaimed asphalt mixtures was evaluated by measuring the mixing torque and determining the air void content of reclaimed mixtures. In addition, their effects on the performances of reclaimed mixture were studied via the three indexes tests, rutting test and freeze-thaw splitting tests. The experimental results show that mixing torque and air void content of reclaimed mixtures with the emulsified rejuvenator is 4% and 6% lower than that with the ordinary rejuvenator, respectively. This indicates that improvement of the workability of reclaimed mixtures can be achieved by using an emulsified rejuvenator, but not by an ordinary rejuvenator. That is also the reason that at least 20% greater high-temperature stability is found for reclaimed mixtures by using the emulsified rejuvenator than using the ordinary rejuvenator. In addition, reclaimed mixtures with the emulsified rejuvenator show similar moisture susceptibility to that with the ordinary rejuvenator. This study provides a feasible method to assess the workability effect of rejuvenators on reclaimed mixtures directly and recommends the use of an emulsified rejuvenator to improve the workability and high-temperature stability of reclaimed mixtures.

The graphene oxide (GO) was used to improve the mechanical performances of epoxy asphalt (EA) by preparing GO/EA composite. The influence of the GO dosage on the micro-structure, curing rheology, mechanical and thermal properties of GO/EA was investigated. According to the XRD and Fourier transform infrared spectra, the GO was exfoliated in the EA matrix and modified EA by non-covalent strategy. GO decreased the rotational viscosity of EA and increased the pot life. The GO/EA with 0.1 wt.% GO showed excellent toughness that the elongation at break was increased by 164%, and the tensile and pull-off adhesion strength were nearly equal to that of EA. The addition of GO improved the original thermal decomposition temperature (T_5%), glass transition temperature (T_g), compatibility and stiffness of the EA. The improved mechanical and thermal properties of GO/EA may be attributed to (1) excellent performances of GO and (2) inhibiting effect of GO on the EA curing process.