Effect of Calcareous Fillers on Bituminous Mix Aging

The aim of this paper is to explain phenomena associated with bitumen aging and to establish design patterns that contribute to optimizing the aging resistance of bituminous mixes on the basis of the rational addition of calcareous fillers (hydrated lime and limestone filler). The potential benefits of using fillers to improve aging resistance are well known. However, concepts related to the biphasic filler-bitumen system affecting some of the main characteristics of mixes are not always considered. In this paper, a new study procedure, Universal de Caracterización de Ligantes, a method for characterizing both conventional and polymer-modified binders developed at the Technical University of Catalonia, has been applied. In addition, the dynamic shear rheometer and nonroutine procedures such as macromolecular analysis (e.g., gel-permeation chromatography and infrared spectroscopy) were used to perform rheological tests. These techniques have provided greater insight into the causes and effects of aging on the basis of changes undergone by the bituminous binder. The obtained results show the advantages of incorporating calcareous fillers into bituminous mixes, provided that filler content does not exceed a critical concentration determined by the type of filler and binder to be used. Moreover, some variations on the concept of critical concentration of filler in bituminous mixes have been found, notably those resulting from the degree of mix aging and use of polymer-modified bitumens.