Microstructure, Morphology, and Failure Modes of Polymer-Modified Asphalts

Abstract

The effects of polymer modification on microstructure, morphology, and failure modes of asphalt binders and their concretes were investigated using various test methodologies that have been newly developed or modified. Results from the good and bad samples (i.e., a new Marshall concrete specimen and an aged road core, flexible pavement that showed signs of stripping, respectively) confirmed the reliability and applicability of the test methods. Two different viscosity-graded asphalt binders, AC-5 and AC-10, with two types of network thermoplastics, styrene-butadiene-styrene and styrene-ethylene-butadiene-styrene block copolymers, were studied for void morphology, binder phase morphology, statistical void image analysis, and failure modes as a function of polymer concentration and test temperature. One of the most striking results is that a highly entangled fibrillar network structure has been observed from both straight and polymer-modified asphalt binders after an electron beam etching. It was also observed that the morphology of the network altered with prestraining or binder aging. Void morphology and statistical void analysis were well characterized with the methods developed, but no significant effect of polymer modification was observed. From the fracture studies, however, the polymer modification indicated strong influence on both microdeformation behavior and failure mode of the asphalt concretes.