Investigating molecular-level factors that affect the durability of restored aged asphalt binder

Abstract

This paper examines the durability of restored aged asphalt in terms of its susceptibility to moisture and aging. The study is motivated by the increasing use of modifiers called rejuvenators that are added to paving mixtures containing reclaimed asphalt pavements to restore the original rheological properties of asphalt binder that have been lost during service life. Although several test methods have been proposed to quantify the restoration capability of rejuvenators, not much attention has been given to the side-effects that the rejuvenators may impart to the resulting mix. Due to the specific chemical composition of certain rejuvenators, they may negatively impact the durability of the mixture, especially pertaining to its resistance to moisture damage and aging. This paper examines several rejuvenators that are all effective at restoring aged asphalt binder’s rheological properties, to highlight plausible side effects that may be overlooked when selection criteria are based solely on the restoration capacity of rejuvenators. Our laboratory experiments and computational analysis geared toward the use of rheometry and density functional theory showed that while all studied rejuvenators restored the rheological properties of aged asphalt binders, they had very different durability in terms of resistance to aging and moisture damage. Results obtained from the dynamic shear rheometer showed the rejuvenators with the highest restoration capacity did not have the best durability. Computational analysis showed that while the restoration capacity of rejuvenators is related to their penetration into and peptizing of asphaltene nanoaggregates, durability is mainly related to their polarizability values. Rejuvenators with lower polarizability showed better resistance to aging and moisture damage. The outcome of the study facilitates production of effective rejuvenators without compromising the long-term durability of restored asphalt binder. It also helps road authorities develop selection metrics that account for durability along with rheological properties, to prevent non-durable rejuvenators from entering the market. Accordingly, the study results promote sustainability and resource conservation by providing an in-depth understanding of the relation between rejuvenators’ chemical structure and the durability of restored aged asphalt binder.