Temperature and thermal history dependence of the microstructure in bituminous materials

Bituminous materials are known to possess microstructures, which can be imaged by atomic force microscopy (AFM). The main objective of this work is to determine the influence of temperature and thermal history on the microstructures of bitumen by means of AFM. Three bitumen samples from different crude sources are studied. Their microstructures are imaged in real time by AFM for various thermal scenarios such as (slow) heating and cooling. It is found that the microstructural features show a tendency to align themselves with increasing temperature. Moreover a hysteresis-like effect in the microstructural properties is observed between the heating and cooling paths. Finally it is found that bitumen possess a 'memory' for its maximum processing temperature. Different maximum processing temperatures lead to different room temperature microstructures of the material. Thus, a bituminous material may be characterized by a 'reset temperature' above which memory of its previous microstructural state is completely erased.