ADSORPTION OF ASPHALTS AND THEIR SIZE-EXCLUSION CHROMATOGRAPHY FRACTIONS ON AGGREGATE SURFACES

The adsorption behavior of two asphalts and their size exclusion chrom atography (SEC) fractions from toluene solution onto aggregate was inv estigated. The effect of the differences in chemistry and molecular si ze of the asphalt samples on their adsorption behavior on silica, gran ite and greywacke was determined. The adsorption of asphalts and SEC f ractions on SI-1000 silica was well-represented by the Toth model, whi le the Radke-Prausnitz model better described their adsorption behavio r on both granite and greywacke. Combining the adsorption models with the Gibbs adsorption equation of state gave the spreading pressure of each adsorbate species adsorbed on the aggregate surfaces. The spreadi ng pressure predicted the competitive adsorptive edge of the asphalt f ractions. The SEC I fractions, containing molecules of larger molecula r size and higher heteroatom contents, showed higher spreading pressur es than the SEC II fractions, which contained molecules of smaller mol ecular size and fewer heteroatoms. The asphalts yielded intermediate s preading pressures for SI-1000 silica and granite, but they gave the h ighest spreading pressure values for greywacke.