Nanoindentation and Atomic Force Microscopy Investigations of Asphalt Binder and Mastic

Abstract

Nanoindentation techniques were implemented to calculate and interpret linear viscoelastic properties of asphalt binder and mastic through low-load spheroconical (blunt) nanoindentation. Experiments on three rolling thin-film oven (RTFO)–aged binders (two neat and one polymer modified) and 24 RTFO-aged mastics were implemented for reproducible creep indentations at ultra low loads. Creep compliance model parameters were extracted and used to determine dynamic modulus values for each material. Dynamic modulus values from nanoindentation were validated by using macroscopic dynamic shear rheometer (DSR) testing for two binders and two mastics (RTFO-aged). Atomic force microscopy (AFM) images of binder and mastic microstructure were obtained to shed insight on how microstructural phenomena relate to mechanical properties. The new results were combined with previously determined work of cohesion values for three binders and 30 mastics (RTFO-aged) made with the same materials to link microstructural phenomena with viscoelastic and cohesive properties of asphalt binder and mastic. The AFM results show microstructural changes occurring with the addition of mineral fillers that may relate to observed trends in nanoindentation viscoelasticity and cohesion data. Testing of binder and mastic properties through nanoindentation is an important step toward in situ testing of mastic in asphalt concrete, which is impossible using conventional macroscopic experimental methods.