Rheological and Chemical Evaluation of Aging Resistant Binder Technologies

Abstract

Asphalt binder is a dark-colored cementitious hydrocarbon material, with a complex chemical composition that is heavily dependent on crude oil source and manufacturing process. Binder chemistry has been modelled as a colloidal system with four main chemical fractions (i.e., SARA fractions) that directly impact binder rheological properties. Binders are subjected to aging mechanisms that cause irreversible changes in their chemical composition throughout the pavement service life. Aging increases the concentration of polar functional groups of asphalt, leading to more molecular association and less molecular mobility. As a result, binders become stiffer and less flexible, making them more brittle. Ultimately, binders become more susceptible to fatigue and thermal cracking, affecting the long-term performance of flexible pavements. This study evaluated aging resistant technologies that can reduce the aging susceptibility of asphalt binders. The evaluated technologies/additives included (1) a blend of biosynthetic oils and petroleum-based oils, (2) a blend of thermosetting epoxy polymer and oil-based flexible modifiers, (3) a sub-epoxidized soybean oil, (4) a hybrid technology composed of a continuous phase styrenic block copolymer with a pine-based chemical additive, and (5) a hybrid system composed of ground tire rubber (GTR) powder and Rheopave®. Each additive was blended with two base binders selected from different crude sources, and their blends with 20 percent reclaimed asphalt pavement (RAP) binder extracted from a RAP source. The aging resistant effectiveness of each technology was evaluated based on their rheological and chemical characteristics before and after multiple aging procedures that included Rolling Thin Film Oven (RTFO), RTFO + 20-hour Pressurized Aging Vessel (PAV) and RTFO + 60-hour PAV. The rheological evaluation included Superpave performance grading, Multiple Stress Creep and Recovery (MSCR) test, Linear Amplitude Sweep (LAS) test, frequency sweep for master curve construction, and extended Bending Beam Rheometer (BBR) test. Chemical testing evaluated the formation of oxidation products through Fourier Transformed Infrared Spectroscopy (FTIR), glass transition and thermal behavior through Differential Scanning Calorimetry (DSC), binder chemical composition through SARA fractions and molecular size distribution using Gel Permeation Chromatography (GPC). Rheological and chemical results showed that the binders modified with the candidate technologies were less affected by aging than the control binders. However, the levels of effect were influenced by a combination of technology, base binder and presence of extracted RAP binder. Overall, the technologies can mitigate the effects of aging, reducing the stiffening and embrittlement of binders. The chemical test results help explain the working mechanisms of these technologies, such as decreased formation of oxidation products (i.e., carbonyl and sulfoxides), and supported the findings observed from the rheological test results.