ADSORPTION OF ASPHALT FUNCTIONALITIES AND OXIDIZED ASPHALTS ON AGGREGATE SURFACES

The adsorption of asphalt functionalities and asphalt oxidized to different degrees on real and model aggregates has been investigated. The functionalities used were: nitrogen-base, phenolic, carboxylic acid, ester, ketone, sulfoxide, and polynuclear aromatic. Adsorption isotherms of these functionalities on porous silica showed different affinity rankings dependent upon concentration. The competitive affinity ranking of the asphalt functionalities on dried silica was obtained as phenylsulfoxide > qulnoline > phenol > benzoic acid > benzophenone > benzylbenzoate > pyrene. The sensitivity to moist silica surface of the four most strongly adsorbed compounds was: qulnoline > benzoic acid > phenol > phenylsulfoxide. Asphalts oxidized to different degrees were adsorbed on different aggregates. On silica and alumina, the oxidized asphalts with viscosities of 32,000 and 126,000 poise were adsorbed less than AC-20. On limestone and sandstone, the adsorption of AC-20 and oxidized asphalts was concentration dependent; asphaltene adsorption followed the same trends. These adsorptions followed the Langrauir isotherm with monolayer coverage decreasing with increased oxidation. functionalities such as ketones produced during oxidation are not as strong adsorbers as other functionalities; thus, changes in chemical composition during oxidation may result in substantial changes in asphalt adsorptive behavior. As oxidation increased in the different asphalts, the monolayer coverages of the asphalts decreased. Aggregate sensitivity to oxidation ranked in the order of silica > alumina > sandstone > limestone. Thus, the adsorptive behavior of an asphalt is a function of both the degree of oxidation and the aggregate onto which it is adsorbing.