Developments in the Rational Mix Design of Bituminous Mixtures: the Effects of Aggregates as Modelled by the Voids Method

The paper contains the results of a series of experimental investigations that were carried out in the Road Materials Laboratory of the Politecnico di Torino in order to improve a previously developed mix design method referred to as the “Voids Method”. Such a method is based on the concept of progressive saturation of the voids present in each aggregate class and leads to the preparation of mixtures with a predefined level of residual voids. The effects deriving from the use of aggregates of three different origins, characterized by different shape and grading, have been examined from a volumetric point of view. Moreover, supplementary design equations have been developed which relate the effective void content (%v) and the effective aggregate packing (VMA) to the variables which are used in the method. In its revised and updated version the design method thus enables the actual structure of the mixture in its compacted state to be predicted from a limited amount of preliminary experimental data regarding the employed aggregates.