Viscoelasticity stage evolution characteristics and multiphase microstructure of aged crumb rubber-modified asphalt

Abstract

Owing to the complex composition of the internal structures of aged crumb rubber-modified asphalt (CRMA), the current understanding of its aging properties and mechanism is lacking. Therefore, this study used the Christensen–Anderson–Marasteanu model, established the master curves of the complex moduli and phase angles of aged CRMA samples, and analyzed the evolution of their viscoelastic properties. Moreover, gel permeation chromatography and scanning electron microscopy were used to characterize the microscopic characteristics of the asphalt and crumb rubber modifier (CRM) phases of the CRMA samples. In aging, the evolution process of the complex modulus and phase angles of CRMAs demonstrated three stages in the low-frequency domain. With the degradation of the CRM, the plateau in the master curves of the phase angles gradually disappeared and the slopes of the Han curves gradually increased. The plateau of phase angle and slope of the Han curve were used as indices to evaluate the degradation of the CRM in the aged CRMA. The microscopic tests demonstrated that the further degradation effect of the CRM degradation products decreased the weight-average molecular weight of the aged CRMA. In addition, the degradation of the CRM probably affected the formation of asphaltene and reduced its content. The CRM of the unaged CRMA exhibited a fluffy structure similar to that of a sponge. As the aging time increased, the surface of the CRM tended to be smooth, the pore structure disappeared, and finally, the fluffy structural form of the CRM disappeared.