COMPATIBILITIES OF STRATEGIC HIGHWAY RESEARCH PROGRAM ASPHALTS

The so-called colloidal model of asphalt structure views asphalts as dispersions of relatively aromatic, polar, associating molecules in a less aromatic, less polar solvent phase. The extent to which solvent phases disperse associating species, therefore, should determine many fundamental properties of asphalts, and measurements of state of dispersion should allow for prediction of important properties. States of dispersion, or compatibility, of eight virgin asphalts studied in the Strategic Highway Research Program were measured by several methods. These methods were the Heithaus titration method, measurements of asphaltene yields by precipitation with n-heptane followed by iso-octane, measurements of relative viscosities (viscosity of asphalt divided by viscosity of maltenes) at different temperatures, and determination of sulfur content. All these methods served to identify two asphalts as being fundamentally much more compatible than the other six. Among the other six less well dispersed, less compatible asphalts, the methods did not serve to differentiate one from another in the same way. For the eight asphalts studied determining the sulfur content or measuring n-heptane asphaltene yields appeared to be equally good as indicators of compatibility as the more complicated methods. Absolute viscosities of asphalts do not correlate with asphalt compatibilities, as is well known. However, relative viscosities determined by dividing asphalt viscosities by maltene viscosities (the maltenes are considered to be the solvent phase) appear to be good indicators of asphalt compatibilities.