Identification of the Composite Relaxation Modulus of Asphalt Binder Using AFM Nanoindentation

Abstract

The use of nanoindentation to study asphalt is aimed at understanding the relationship between properties of asphalt binder at various length scales. A combination of atomic force microscopy (AFM) imaging and nanoindentation is used to determine the relaxation moduli of bimodal and trimodal distributions of asphalt microphases to assess differences between macroscale and composite nanoscale viscoelastic behavior. The relaxation modulus values extracted from age-altered phases of the same asphalts provide important relationships between microstructural changes depicted in AFM images and changes in composite viscoelastic properties obtained from the measurements. This paper provides key information regarding asphalt microrheology, which will yield improved input values for asphalt prediction models and enhanced pavement performance. Based on comparison of the composite viscoelastic properties obtained from this study to values obtained at larger length scales, it is apparent that relaxation modulus values decrease as the length scale increases. This finding serves as the basis for ongoing studies by the authors and other researchers in the areas of asphalt nanomodification, chemical mapping, and modeling of nanodamage using AFM.