Investigating bonding mechanism of rubberized RAP asphalt mastic from rheological and physiochemical perspectives

Considering the enormous amounts of virgin materials consumed in road construction and rehabilitation, recycling reclaimed asphalt pavement has aroused great interest recently. Among different modifiers, crumb rubber is a waste material that significantly enhances different characteristics of the asphalt binder. This study investigates the bonding strength of asphalt mastic of reclaimed asphalt binder modified by crumb rubber-modified binder. The study also attempts to model the mastic bonding strength and understand its mechanism. Thirty binders with different percentages of crumb rubber and reclaimed asphalt were mixed with two filler types to produce the asphalt mastics. Moreover, the two phases of the binder colloid, gel and liquid phases, created by crumb rubber modification, were separated to evaluate the crumb rubber interaction and its impact on mastic bonding. The pull-off test was used to evaluate the bonding strength of asphalt mastics and binders, while dynamic shear rheometer and Fourier-transformed infrared spectroscopy were used to evaluate the physiochemical and rheological characteristics of the asphalt binders. The results show that crumb rubber and reclaimed asphalt modifications greatly strengthen the mastic bonding. The accretion of carbonyl groups due to the reclaimed asphalt addition and withdrawal of light components due to the crumb rubber interaction improves the stiffness of the liquid phase binder, which is strongly correlated to the mastic bonding strength. Furthermore, despite its role in strengthening the binder stiffness, the crumb rubber particles as fillers no longer affect the mastic bonding, where this role is undermined by the mineral fillers.