Selective Absorption of Asphalt Binder by Limestone Aggregates in Asphalt Mixtures

Abstract

It has been found that aggregates used in paving asphalt mixtures absorb the asphalt binder into the porous structure of the aggregates. National test methods are available to measure the aggregate absorption. However, most research and measurements on aggregate absorption are limited to the accessible voids at the aggregate surface. This paper presents recent findings on the selective absorption of asphalt binder by aggregate particles in asphalt mixtures. The selective absorption of the binder is visualized on the aggregate surface under natural light and ultraviolet light. Rings with different colors are identified on the cross sections of the aggregates in both hot-mix asphalt and warm-mix asphalt, which indicates different asphalt components at different radial distances from the center of the aggregates. The asphalt components penetrating into aggregates are verified using the laser desorption ionization–ion mobility–mass spectrometer. A significantly higher concentration of asphalt components is identified at the edge of the limestone sample than in its center after it is soaked in a PG 58-28 asphalt binder (labeled AAD) for 32 h. Creep tests are also conducted on fresh limestone samples and limestone samples soaked in the AAD binder. The fresh limestone sample behaves elastically and is approximately twice as stiff as the sample soaked in the binder, which exhibits nonnegligible viscoelastic properties in the creep test.