https://orcid.org/0000-0001-6288-230X
ABSTRACT
The primary objective of this paper is to investigate the thermoreversible aging mechanism of crumb rubber–modified asphalt binders (CRMAs). In order to achieve this goal, an extended bending beam rheometer (Ex-BBR) test and volumetric dilatometer test were conducted. Additionally, isothermal crystallization kinetics (Avrami theory) and thermal stress calculation using the Hopkins and Hamming algorithm were employed to process the test data. The low-temperature properties of the asphalt specimens were characterized through calculations of creep stiffness (S), creep rate (m-value), grade loss (GL), thermal stress, and Avrami index (n). The experimental results indicate that thermoreversible aging is present in all asphalt samples during the long-term isothermal hardening process. This aging is characterized by continuous macroscopic volume shrinkage, accumulation of thermal stress, a crystallization process, and a process akin to crystallization (i.e., crumb rubber adsorbed oil at low temperatures). It was observed that CRMAs exhibit more severe thermoreversible aging and faster physical hardening rates due to their unique properties at a constant low temperature when compared with base asphalts. However, it was also observed that CRMAs can reduce the thermal stress by reducing the volumetric shrinkage coefficients and S. It is important to note that the volumetric shrinkage coefficients are not constant, which are related to the base asphalts, crumb rubber, and conditioning time. Therefore, it is not appropriate to use a single empirical constant to calculate thermal stress. Instead, multiple coefficients may need to be incorporated to account for the variability in shrinkage behavior.
