INFLUENCE OF AGGREGATE CHEMISTRY ON THE ADSORPTION AND DESORPTION OF ASPHALT

Abstract

Asphalt-aggregate interactions were investigated by evaluating the adsorption and desorption of aged and unaged asphalts on four aggregates: limestone, greywacke, gravel, and basalt. The aggregate composition and surface chemistry had a greater effect on the adsorption and desorption characteristics of the asphalt-aggregate pair than the properties of the asphalt did. Adsorption and desorption isotherms were fitted to the Langmiur model and yielded predicted monolayer amounts, equilibrium constants for adsorption, and Gibbs free energy of adsorption. The Gibbs free energies were evaluated in terms of the principles of soil mechanics, which showed that water in the voids can be drawn to the asphalt-aggregate interface at relative humidities of 99% or above. Estimates of minimum tensile strength ratios were determined from Gibbs free energies and the extrapolated measured enthalpy values. The presence of water at the interface reduces the Gibbs free energy values between the asphalt and aggregate, thereby reducing the tensile strength and resistance to debonding fracture.