Evaluation of Bitumen-Aggregate Interactions by Means of Volumetric Expansion Tests

In this paper the Authors propose the use of as test method with which the thin layer of bitumen which coats aggregate particles in a bituminous mixture is subjected to an approximately uniform state of tension. This is done by means of a high vacuum system and of measurements of the specific volume of bitumen-aggregate mixtures at less than atmospheric, progressively lower pressure levels. Volumetric variations may be thus assumed to be a combined measure of the binder stiffness and of its interaction with the mineral surface. It was found that specific volume varies in a non linear way with respect to pressure level due to particular interaction phenomena which are aggregate and binder dependent. In the paper these phenomena are described by means of a simple interpretation model. Finally, a discussion of the effects on test results caused by a number of test and material variables is presented.