Physicochemical characterization of short and long-term aged asphalt mixtures for low-temperature performance

•Rheological changes in 36 different asphalt mixtures due to variable RAP content and aging period.•Fourier-Transform Infrared Spectroscopy (FT-IR) of extracted aged binders from Bending Beam Rheometer (BBR) Specimens.•Natural long-term aging of the BBR specimens for three years outdoors.•Relative distribution, mapping and detection of micro-cracks using SEM-EDX. Current pavement engineering shift towards Balanced Mix Design warrants performance testing of asphalt mixtures at low temperatures. The Bending Beam Rheometer (BBR) is an effective tool to characterize asphalt mixture’s low-temperature properties based on AASHTO TP125. This study utilized the BBR for physical characterization of 32 different asphalt mixtures composed of a PG 64–28 binder, two Job-Mix Formulae (JMF), four different RAP contents, and four different aging methods. Chemically extracted binder from the aged mixtures was then analyzed using the absorbance-based Fourier-Transform Infrared Spectroscopy (FT-IR) to identify the critical functional groups. The FT-IR analysis's semi-quantitative results were validated using the Energy Dispersive X-Ray Analyzer on the Scanning Electron Microscope (SEM-EDX). The reduction of carbon and sulfur concentration due to oxidation was correlated to the loss of cohesion between asphalt mastic and aggregates. Furthermore, microstructural damage was found in the aged specimens at a 200x magnification. Overall, this study provides a comprehensive and feasible method to perform physicochemical characterization of asphalt mixtures.