Nanomechanical Evaluation of Vapor-Conditioned and Unconditioned Asphalt

Abstract

Traditionally, moisture damage of asphalt concrete (AC) is evaluated by comparing the macroscale strength and stiffness values of a set of moisture- or vapor-conditioned samples with those of a set of unconditioned AC samples. The moisture damage of a bulk (liquid) asphalt binder is determined by the surface energy components of the binder with a Wilhelmy plate device: the most recent and advanced way to evaluate moisture damage in liquid asphalt. Despite these advancements, moisture damage in AC or asphalt binder is an unsolved issue. Different from previous approaches, this study evaluated the moisture damage of thin films of asphalt deposited on glass substrates, conditioned at 25%, 49%, and 71% vapors, and used a nanoindentation technique for testing. In nanoindentation, a point load indents the asphalt film surface and load–displacement data are recorded. The study analyzed nanoindentation data with the traditional Oliver–Pharr method and a nontraditional mechanical model that captures the viscoelastoplastic behavior of the indented film with spring, dashpot, and rigid (SDR) body elements. The model results showed that the modulus and hardness of asphalt film decreased with an increase in vapor level. The SDR model showed that at higher humidity, at 49% and 71% humidity conditions, the viscosity decreased by approximately 60% in thin film binder.