Interaction of Asphalt Films with Aggregate Surfaces in the Presence of Water

ABSTRACT Experiments were conducted to investigate the effects of water on mixtures of neat asphalts with two aggregates. In these experiments, samples of mixtures were contacted with warm water for varying lengths of time. When the samples were removed from water, they were dried and then were contacted with n-heptane. This relatively inert solvent dissolves maltenes, precipitates asphaltenes, and should not disturb polar organic molecules of asphalts adsorbed on aggregate surfaces during water soaking. The polar organics then were recovered using a polar solvent and were weighed and studied by infrared spectrometry. The polar organics recovered were adsorbed from neat asphalts and not solutions of asphalts as in other studies. Measurements of the pH of waters in contact with the mixtures indicate that water rapidly penetrates to asphalt-aggregate interfaces in most of the systems studied. In some systems, amounts of polar organics recovered did not change with soak time. In others, amounts of polar organics increased as a result of water soaking, particularly a combination of a waxy asphalt with granite. The infrared results showed that some carbonyl compounds and 2-quinolones are readily displaced from aggregate surfaces by water, as was found in the solvent studies. Sulfoxide groups do not appear to be as labile. Each asphalt-aggregate combination appears to exhibit a characteristic response to water, as is observed in pavements.