CHEMICAL COMPOSITION OF ASPHALT AS RELATED TO ASPHALT DURABILITY: STATE OF THE ART

The literature on asphalt chemical composition and asphalt durability has been reviewed and interpreted relative to the current state of the art. Two major chemical factors affecting asphalt durability are the compatibility of the interacting components of asphalt and the resistance of the asphalt to change from oxidative aging. Historically, studies of the chemical components of asphalt have been facilitated by separation of asphalt into component fractions, sometimes called generic fractions; however, these fractions are still complex mixtures the composition of which can vary significantly among asphalts of different sources. The reaction of asphalt with atmospheric oxygen is a major factor leading to the hardening and embrittlement of asphalt. The hardening phenomenon is primarily a result of the formation in asphalt of polar oxygencontaining functional groups that increase asphalt consistency through strong molecular interaction forces. The identification and characterization of the chemical functional types normally present in asphalt or formed on oxidative aging that influence molecular interactions afford a fundamental approach to relating asphalt composition with asphalt properties and thus the performance of both asphalts and asphalt-aggregate mixtures. In addition to the polar chemical functional groups formed on oxidation, asphalt properties can also be significantly altered by molecular structuring, sometimes called steric hardening. This potentially reversible phenomenon, although highly elusive and difficult to quantify in asphalt pavement mixtures, may also be a major factor contributing to pavement embrittlement.