This paper describes an investigation into the type and water resistivity of asphalt-aggregate bonding which was undertaken in the SHRP A-003B contract. Specifically, the adsorption and desorption of asphalt and asphalt models, with functional groups similar to those present in asphalt, on siliceous and calcareous aggregates have been examined. The adsorption of asphalt models has shown that the amount adsorbed is dependent on the chemical properties of both the asphalt model and the aggregate. The more polar models, such as benzoic acid and phenylsulfoxide, adsorbed in larger quantities on all the aggregates than did the less polar models, such as indole and pyrene. The adsorption behaviour is also strongly dependent on the chemistry of the aggregate surface. Desorption has been performed using both large and small quantities of water. The desorption behaviour is dependent on the polarity of the asphalt models and on the quantity of water used. Modification of the aggregate surface can cause enhancement or reduction in the adsorption and desorption of the asphaltic model. Asphalt adsorption and desorption on both siliceous and calcareous aggregates have shown that the asphalt chemical composition affects the amount of asphalt adsorbed and desorbed. Even more pronounced is the effect of aggregate chemistry on asphalt adsorption and desorption behaviour. For any given asphalt, substantial differences are observed for the net adsorption, i.e., amount of asphalt remaining on the aggregate surface after desorption by water, on different aggregate types. Changes to the aggregate surface by modification canresult in changing the net adsorption. The extent of change is dependent upon the chemistry and degree of coverage of the modifier. Addition of antistripping agents to the asphalt results in a lowering of both the initial amount of asphalt adsorbed as well as the amount desorbed. This methodology is being developed into a test method for selecting good performing asphalt-aggregate pairs.
Samenvatting