ABSTRACT
In this paper the authors propose the use of a 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.
