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With the increasing environmental awareness and rising costs of virgin binders, reclaimed asphalt pavement (RAP) has been used as an alternative for energy and cost saving in asphalt pavements. However, RAP binders have been aged to different extents during pavements’ service life and adding rejuvenating agents provides a practical means for restoring the mechanical properties of the aged binders reducing the needed additional virgin binder. In many studies, the rejuvenating effect has been evaluated in terms of the improvement of rejuvenated binders’ rheological properties whereas the fundamental rejuvenation mechanism remains unclear. In this research, two different asphalt binders from the Materials Reference Library of the Strategic Highway Research Program (SHRP) were aged, and rejuvenated by complete blending with two commonly used rejuvenators. The rheological properties of the virgin, aged, and rejuvenated binders were tested using the dynamic shear rheometer and the bending beam rheometer. Furthermore, in order to better understand the rejuvenating effect, surface microscopic properties and chemical composition of the binders were measured using atomic force microscopy (AFM) and SARA (Saturates, Aromatics, Resins, Asphaltenes) fractionation, respectively. Results indicated that the bulk mechanical properties (complex modulus and viscosity) of the rejuvenated binders were in between those of the virgin and aged binders. Aging and rejuvenation led to morphological changes as compared to their virgin binders; however, the rejuvenated binders did not always reproduce the microstructures of the virgin binders. Microscopic measurements on adhesion and dissipation of virgin, aged, and rejuvenated samples were qualitatively consistent with the bulk rheological results. SARA separation results suggested that changes in chemical fractions were responsible for the stiffening effect of aging and the improvement of mechanical properties with the addition of the rejuvenators. Such a systematic approach of characterizing the rejuvenating mechanism will benefit the effort of producing more sustainable RAP-containing asphalt pavements. |
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