Shifting the bitumen structure from sol to gel

The theory of the colloidal structure of bitumens, although not universally accepted, is one of the most known. Besides the speculative discussion on this subject, some practical aspects of this theory can be considered; in particular, the sol–gel characteristics of bitumens seem to significantly affect their performances in road application. In this regard, rheological tests carried out with modern rheometers appear particularly promising to investigate such aspects. Moreover, the ability of the bitumen to blend with some polymers changes with its colloidal state, which influences its behavior in a two-phase system. In the present work the sol–gel structure of two series of blown bitumens (at various degrees of oxidation) and of a series of chemically treated bitumens were investigated. In particular, Tgδ (=G″/G′) vs. temperature plots and Cole–Cole plots generated with a dynamic, controlled shear rheometer, provided information on high temperature performances and macroscopic structure, respectively. Stability studies have also been carried out on bitumens modified with a new class of polymers (polypropylene heterophasic copolymers), before and after physical (high temperature blowing) or chemical (acid addition) treatments.