Comparison of ESEM and physical properties of virgin and laboratory aged asphalt binders

Abstract

The physical and microstructural properties of four straight run asphalt binders were examined and compared in combination with short term aging (RTFOT) and long-term (PAV) laboratory aging. RTFOT aging was conducted at temperatures of 123, 143 and 163 °C. The physical testing parameters included penetration, softening point and Dynamic Shear Rheology (DSR) complex shear modulus and phase angle at 10 °C. The binders selected came from four different sources and had the same penetration grading (70/100). They all showed an increase in stiffness with aging, including with the increase in RTFOT temperatures and especially with PAV aging. The microstructural evolution of the binder was examined by Environmental Scanning Electron Microscopy (ESEM) on aged binders at 123 and 163 °C. The physical changes with aging corresponded to an evolution in the binders’ ‘fibril’ microstructure under ESEM, as a result of electron beam exposure, with the microstructure getting denser with PAV aging. This densification (fibril area) of the microstructure was quantified with image analysis for the virgin and RTFOT aged samples, and the fibril formation time was also measured. The asphalt binders showed varied ESEM ‘fingerprints’ and aged in different ways. The ESEM ‘formation time’ and ‘fibril area’ of the binders generally showed good correlation with the physical properties, although this was not the case for all of the binders due to their unique aging characteristics.