A Literature Review of Bitumen Hardening from Past to Present: Aging Mechanism, Indicators, Test Methods, and Retarders

摘要

Bitumen-a by-product of crude oil-is a rheological material whose properties undergo deforming changes caused not only by the effects of physical loads and loading duration but also by exposure to environmental factors and variations of temperature. The typical properties of the ultimate bitumen in-service differ greatly from those of the initial bitumen in terms of getting more viscous, stiffer, and more fragile as a result of the age-hardening, and worse still, this process is almost inevitable. Excessive aging may cause the binder to partially lose its adhesion and cohesion, and subsequently it may cause some detrimental distresses in bituminous pavements such as raveling and graveling. The current study represents an elaborate investigation into the pivotal phenomena provoking bitumen aging. Furthermore, several quantitative indicators to determine the level of hardening are discussed and a state of the art on past and current protocols to emulate aging in laboratory environment is provided. Finally, this paper highlights the inclusion of various anti-aging agents to palliate the aging of binder in order to improve the resistance of bituminous mixtures.