Road bitumen undergoes, during its service life, an ageing process that leads to a material's hardening. But, when a polymer modified bitumen (PmB) has been used, what happens after oxidation/ageing is very complex to analyse, due to the number of chemical parameters involved: the nature of the polymer (structure and chemistry), the chemistry of bitumen, and the type of blending. The chapter begins by describing the main physicochemical and rheological methods that are the most appropriate to study PmB and also to follow their evolution during thermal or photo-ageing. It then presents a new way of characterizing these heterogeneous products by infrared microscopy without modifying the internal equilibrium between polymeric and bituminous phases. The chapter includes the results of an investigation, at the microscopic scale, of PmB ageing so as to understand how any changes in composition or processing affect PmB evolution with time.
