Different Forms of Asphaltene Microstructures Discovered in Transmission Electron Microscopy

Two forms of microstructures in different types of asphaltenes and asphalt binder samples were discovered by using transmission electron microscopy (TEM). The first type of the microstructures is needle-shaped with a crystalline structure, while the second type is plate-shaped without a regular pattern. The size of the microstructures ranges from a few nanometers to several micrometers. The microstructures are more prevalent in field-aged asphalt binder and asphaltenes samples than those in nonaged ones. Experimental results indicate that both forms of microstructures are not made of wax, but asphaltenes molecules. The two forms of asphaltenes microstructures differ in morphology, microscopic structure, chemical composition, and resistance to electron radiation damage, indicating that they are formed by different mechanisms and have different physicochemical properties. Both types of microstructures also show thermal stability at elevated temperatures. The prevalence, size, and shape of the microstructures in field-aged asphalt binder may impart significant impacts on binder engineering properties in pavement use as well as its behaviors in recycling or rejuvenation. Hence, the microstructures are believed to be the key to understanding asphalt binder aging, aging control/reversal methods. More studies are needed to investigate the newly found microstructures. (C) 2016 American Society of Civil Engineers.