Additives on aged bitumens: What probe to distinguish between rejuvenating and fluxing effects?

Bitumen is a complex material used for road pavement throughout the world. During paving and pavement service life loss of more volatile compounds and oxidization takes place. Hence, asphaltene micelles become larger so that the fluidity of the system is reduced; the material becomes rigid, stiff and brittle so needing replacement. Once removed, it can be processed to restore its original properties and used for Reclaimed Asphalt Pavement (RAP). For such a process, additives called “rejuvenators” are used: they act on the chemical structure of aged bitumen to restore its physical properties to a state very similar to virgin bitumen. Alternatively, softening agents can be used to restore only the physical properties. An additive conferring regenerating characteristic on the asphalt mix increases the longevity of asphalt pavements due to the fact that it brings the bitumen back to its initial state; on the other hand, softening agents render the aged bitumen more workable but road pavements remain rigid and eventually break in the course of use. At the moment, methods that can distinguish a regenerating effect from a fluxing effect are not known. This study aims at evaluating the different effects of the additives on aged bitumen. For this purpose, we used a commercial additive (tritolyl poly phosphate, TPI) working as rejuvenator and a softening agent (soy oil) which is a well-known fluxing agent. The effects of the additives on aged bitumen have been investigated through Dynamic Shear Rheometer, Atomic Force Microscopy, Optical Microscopy and Infrared Spectroscopy.