The relative amounts and characteristics of asphaltenes, oils, and resins in a given asphalt have an important effect on its physical characteristics and value as a paving material. A more recent procedure to separate asphalt into fractions of various molecular sizes is high pressure-gel permeation chromatography (hp-gpc). This procedure can be used to classify asphalt molecules into three groups according to their molecular size: large molecular size (lms), medium molecular size (mms), and small molecular size (sms). The balance between the relative amounts of these molecules is an important attribute of asphalt durability and its ability to perform properly in paving mixtures. This paper presents a study in which the changes in properties of a virgin ac-20 (astm designated) due to aging are characterized by means of the hp-gpc. Furthermore, molecular size distribution analysis was used to characterize mobilsol-30 (a recycling agent)and to determine the proper amount required to restore salvaged binders to an ac-20 specification range. In addition, the changes in properties due to aging of the weathered binder that had been restoredto an ac-20 specification range were also characterized by means ofthe hp-gpc. It was concluded that the weathering actions (simulatedin the laboratory) would cause increases in lms and decreases in mms and sms. These changes may be detrimental to asphalt characteristics because they result in drastic changes in asphalt consistency. A greater amount of a specific recycling agent is required to restore a more age-hardened binder to its original consistency; hence, the more the molecular size distribution moves away from the original balance. This could be resolved, however, by using different types of recycling agents for different hardening levels of salvaged asphalt or by using more than one recycling agent in proper proportions. Temperature susceptibility may be affected when high percentages of recycling agents are required because of severe hardening characteristics of the salvaged asphalt binder. The hp-gpc analysis for the virginand recycled asphalt binders may be recommended as a criterion for the choice of the proper amount and characteristics of a recycling agent to be used to rejuvenate salvaged asphalt. This paper appears in transportation research record no. 1228, Asphalt mixtures and asphalt chemistry.
Samenvatting