Comparison of microscopic techniques to study the diversity of the bitumen microstructure

Bitumen characterisation and differentiation usually involve a combination of mechanical and chemical analyses. However, these methods provide limited information on the diversity caused by the binders' origin or processing method. Thus, the question arises whether the bitumen microstructure can be used to identify these issues. In this study, microscopic methods, including brightfield, darkfield and fluorescence optical inverse microscopy (OIM), as well as confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM), were used to investigate the bitumen surface. Five different binders varying in their origin and production method were selected. The results show that CLSM, AFM and OIM darkfield can adequately capture a specific surface microstructure known as the bee structure, whereas brightfield in the OIM and optical CLSM show the surrounding peri phase, which exhibits a strong fluorescence. All visbroken binders show bee structures surrounded by a pronounced peri phase. On the other hand, one of the straight distilled binders does not show any microstructure, while the second straight distilled binder displays smaller bee structures surrounded by a small peri phase. Results from the image processing evaluation reveal that the area covered by bee structures is in the range of 2.4 - 4.3% for those binders that developed a surface microstructure. These results indicate a good accordance between the three microscopic techniques selected. However, a clear differentiation between the binders is difficult to obtain. Nonetheless, this work shows how these techniques can be used to their maximum capabilities regarding the obtained microstructural information and may help solve future questions regarding ageing, modification or rejuvenation.

Automated summary

This study utilized multiple microscopic techniques to investigate the microstructure of different binders. The results showed that these techniques were able to capture specific surface microstructures of the binders, but clear differentiation between the binders was difficult to obtain.