Assessment of the digestion time of asphalt rubber binder based on microscopy analysis

One of the most promising techniques for increasing the performance of pavement rehabilitation is the use of asphalt rubber mixtures, which utilize crumb rubber from used tires for modifying the asphalt to produce asphalt rubber binder. Crumb rubber can be produced by two different types of grinding, ambient and cryogenic. The asphalt rubber binder used in asphalt rubber mixtures can be obtained through two different processes, terminal blending (produced at a refinery) and continuous blending (produced in a plant). Because the performance of the asphalt rubber binder depends on the elastomeric properties of the crumb rubber, the manufacturing process, especially the digestion time, influences these properties. The digestion time is responsible for the interaction between the crumb rubber and the straight asphalt, which is characterized by the amount of elastomeric properties transferred to the straight asphalt. This paper presents an assessment of the digestion time using conventional performance-related tests and scanning electron microscopy analyses, which examined the surface of asphalt rubber binder. In this study, two straight asphalts with different penetrations and two crumb rubbers, an ambient crumb rubber and a cryogenic crumb rubber, were considered. The asphalt rubber binders studied in this work were produced using different contents of crumb rubber and different digestion times. The objective of this work is to contribute to the assessment of the digestion time of asphalt rubber binder based on microscopy analysis. This paper concluded that scanning electron microscopy is an important tool for defining the digestion time of asphalt rubber binder.