Nanomechanistic Properties Of Reclaimed Asphalt Pavement Modified Asphalt Binders Using An Atomic Force Microscope

In recent years, the use of reclaimed asphalt pavement (RAP) in pavement construction has become a common practice in the U.S. Addition of RAP with virgin asphalts alters the properties of base binders, resulting in a different in-service performance. Superpave tests are routinely used to characterise modified asphalt binders even though they are applicable for unmodified binders and cannot capture properties of modified asphalts. Recently, several researchers used Atomic Force Microscopy (AFM) techniques to characterise asphalt binders at an atomic level. In this study, binders from two field RAP samples collected from I-40 and I-30 in Arkansas were recovered using a Rotavapor (AASHTO T 319-08). Different amounts (25, 40, and 60%) of RAP binders were blended with a Performance Grade (PG 64-22) binder. Selected microscale (stiffness) and nanoscale (e.g. morphology and elastic modulus) properties of the blended binders were evaluated in the laboratory through test results obtained from selected Superpave tests and the PeakForce Quantitative Nanomechanical Mapping (TM) (PFQNM) mode of an AFM, respectively. As expected, the addition of RAP binder with the base binder increased the stiffness, thereby increasing the high PG temperature up to 85 degrees C for 60% RAP. The micro-structures as well as the nanomechanistic properties of the blended binders were found significantly different from those of the base binder; the elastic modulus of 60% RAP was over 70% higher than that of the base binder. The modulus was found to be correlated with the morphology. The nanoscale properties were in agreement with microscale properties of the tested binders.