Studies show that each kind of fiber has its own advantages in improving the properties of asphalt binders. However, there are very limited research studies about mixed fiber-reinforced asphalt (MFRA). In this study, two kinds of fibers, basalt fiber (BF) and lignin fiber (LF), were selected to reinforce SBS (styrene–butadiene–styrene triblock copolymer)-modified asphalt, which is now widely used in pavement engineering. MFRA samples with different fiber mix ratios (FMRs) were prepared for the tests of softening point, ductility, and rheological properties, the micromorphology of which was studied by using scanning electron microscope (SEM). The oil (asphalt) absorption rates of mixed fibers with different FMRs were also tested. The results show that the properties of MFRA were affected by the physical and chemical properties of fibers. Basalt fiber can better strengthen the physical properties of MFRA, while lignin fiber is good for improving the rheological properties, and the oil absorption rate of lignin fiber is higher than that of basalt fiber. Furthermore, the best FMR calculated by the efficacy coefficient method (ECM) was recommended as 1:2 (BF:LF). An interface layer between the fiber and asphalt was observed from the micro images, proving that the fibers bond well with the asphalt. Generally, mixing BF and LF together into SBS-modified asphalt could make full use of the advantages of different fibers and reinforce the comprehensive performance of MFRA better.

Fluorescent technique has been used to characterise the morphology of polymer modified bitumen for years. However, the main problem of this technique is a missing standardised protocol for image capture factors and processing algorithms (CF&PA). The purpose of this study was to find out the effects of CF&PA on morphology and set up a protocol for morphological analysis of SBS polymer-modified bitumen (PMB) using the fluorescent microscopy technique. In order to set up this protocol, fluorescent images were captured and processed with different CF&PA. Capture factors mainly include magnification, exposure time and storage format while processing algorithms include noise reduction, enhancement and segmentation. Morphological and parametric analysis indicated that all images must be captured under the same exposure time and should not be processed by white balance. Besides, four principles should be followed to determine the optimal magnification. As to the image storage format, JPEG 2000 was selected to retain the most details. The proper neighbourhood level was obtained from the particle number curve to realise noise reduction. Compared with other complicated segmentation algorithms, threshold methods are more suitable because of the typical two-phase characteristic of PMB. Because of potential change in detailed information of original images, enhancement was not recommended. Finally, the image capturing and processing steps and their levels were given based on the discussion above.

Terminal blend rubberized asphalt (TBRA) is widely used as binder of asphalt mixtures due to its technical characteristics of storage stability. However, its road performance deteriorates due to the aging process of TBRA. The purpose of this study is to evaluate the aging characteristics of TBRA binders containing 0%, 5%, 10%, 15%, and 20% content of crumb rubber (CR) by weight of the neat binder. All the binders were treated with rolling thin-film oven test (RTFOT) and pressure aging vessel (PAV), respectively. The chemical compositional changes were monitored by attenuated total reflection (ATR)-Fourier transform infrared spectroscopy (FTIR), and physical and rheological properties were tested on neat asphalt and TBRA binders. FTIR test results show that TBRA binders offer greater long-term aging resistance than the neat asphalt binder, and E10TB (10% by weight CR) exhibits the highest long-term aging resistance. With the increase of CR, the temperature sensitivity property of the TBRA binders increases, whereas their high-temperature stability decreases. After PAV aging, blending CRs into neat asphalt causes a higher phase angle aging index and $J_{nr}$ aging index, and lower critical temperature aging index, complex modulus aging index, softening point increment, and rutting factor aging index, indicating their superior long-term aging resistance. Moreover, based on the correlation analysis, the critical temperature aging index (CTAI) has a good linear relationship with the physical aging index (SPI) and chemical aging index ($\mathrm{\Delta }{I}_{\mathrm{CA}}$ ).