Changjiang Kou

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.

Analysis of microcosmic morphology is significant to the quantitative performance evaluation of polymer-modified bitumen. Diverse methods to prepare observation samples have been used by many scholars but a standard method has not been established. In this study, various preparation methods, namely, hot bitumen dripping on microscope slides (HBDM), frozen bitumen fracture with mechanics (FBFM), and improved method, hot bitumen molding into metal wares (HBMM), were evaluated in terms of influence factors, observation effect, and microcosmic morphology parameters using styrene–butadiene–styrene block copolymer modified bitumen. Results indicate that traditional  observation sample preparation methods are such susceptible to external force, temperature, and some other manual factors that obtaining samples with good reproducibility and stability is difficult. HBDM cannot ensure surface smoothness. Applying pressure on a sample by a cover slip inflates and stretches the polymer phase while heating under microscope slides changes the original morphology of the sample. Due to flexural–tensile and shearing stresses, mechanical force influences the microcosmic morphology and section smoothness of
samples acquired by FBFM. Compared with traditional methods, the improved method (i.e., HBMM) can make up for the disadvantages. Finally, appropriate size and storage temperature for HBMM were given to obtain observation samples with low variability.

Polymer modified asphalt is a typical two-phase blends, and analyzing the phase structure is the most effective way to study its modification mechanism and modification effect. Four microscopic morphological parameters were extracted from fluorescence microscope microscopic images of SBS modified asphalt through professional image processing and analysis software. Then we analyzed each microscopic morphological parameter and corresponding phase structure. The results showed that the area-max is more suitable than the other parameters in characterizing the phase structure of SBS modified asphalt. Area-max 2500μm2 and 13000μm2 can be regarded as the critical point of phase transition. Modifier content is the most directreason for the phase structure changes of polymer modified asphalt. The structure of the polymer phase would not change with the shearing time normally, but in the vicinity of the phase transition critical point, shearing time would have a significant influence on phase structure.

The observation of asphalt binder microstructure with the Environmental Scanning Electron Microscope (ESEM) has yielded promising results. There have been findings that show the microstructure evolving with aging and certain loading applications. The goal of this study was to observe the PMA microstructure using ESEM analysis. Four PMA binders of varying PG grades were observed in ESEM, comparing them to a straight run binder. The binders were compared in terms of the fibril diameter and shape observed visually, along with the fibril structure. The initial ‘bee’ structures before the appearance of the fibrils were also compared. It was found that the PMA binders had a denser fibril structure, corresponding to their higher PG grades indicating stiffer binders, although this varied with different PMAs. The images were also analyzed by calculating the area and length of the fibrils through an image analysis protocol. This study is a step towards the further understanding of the microstructure of PMAs.

Development of fluorescent morphology makes microstructure evaluation of Polymer Modified Bitumen (PMB) become more accurate and scientific. However, it is
still difficult to evaluate the pavement performance of PMB directly by fluorescent morphological images. In this study, PMB was prepared by traditional high-speed shearing emulsifying machine. And then, fluorescent observation samples were prepared using an improved method, pouring hot bitumen into metalwares at the same time with preparing pavement performance test samples. It can guarantee both sample primitiveness and data synchronism. Image capture factors and process methods were determined by morphology analysis. On the premise of these operations, reliable binary images could be gotten with good reproducibility and authenticity. Microscopic data describing the morphology characteristic were extracted from these images. Finally, by stepwise regression analysis, morphology parameters contributing greater to pavement performance of PMB were selected to express the microscopic mechanism of macro-performance in the form of linear equation. Results indicate that multiple linear equation can explain the influence of morphology parameters on pavement performances
well according to their test mechanism. Besides, regression coefficients have definite physical significance.