Investigation of Sterol Chemistry to Retard the Aging of Asphalt Binders

Abstract

The addition of petroleum-derived oils (aromatic or paraffinic) and bioderived oils (typically low-viscosity, unsaturated hydrocarbons modified to remove acid functionality) to bitumen has become a burgeoning business to facilitate the use of increasing amounts of reclaimed asphalt pavement, reclaimed asphalt shingles (RAS), and combinations. These additives have been marketed as softening agents, to reduce high- and low-temperature performance grades, and as rejuvenators. Given the aging mechanism of bitumen and chemical changes that occur during aging, it is unlikely that any true form of rejuvenation is possible. In this paper data are provided on investigations into the use of a chemical class known as sterols, which can be obtained from seed oils and tall oil to retard the aging of bitumen. Investigations were carried out with RAS, with re-refined engine oil bottoms, and with the accelerated aging of bitumen and bituminous mixtures that contained sterol chemistry. The results demonstrated that, relative to controls without sterol, increases in the bitumen rheological index were reduced, and decreases in the colloidal index were reduced, as were decreases in the difference between bitumen low-temperature stiffness critical temperature and bitumen m-value critical temperature (ΔTc). Investigations with atomic force microscopy of bitumen samples with sterol additive, compared with those without, were used to understand the sterol additive function as the bitumen was aged.