Response of the microstructure of bitumen upon stress–damage initiation and recovery

The occurrence of discrete cracking of bitumen and asphalt is difficult to observe/analyse mainly because of the viscous nature of the bitumen binder. Many techniques simply do not have the required resolution or analysis techniques do not get a good response from the highly dissipative bitumen. In this study, an attempt is made to visualise failure development under straining conditions in bitumen with the use of an in situ tensile tester combined with atomic force microscopy. From the experiments, it was observed that cracks or strain localisations occur in the perpetua phase though only significantly for aged binder (i.e. more than six months at room temperature). Furthermore, the locations of these cracks or strain localisations occur on the edges of the more rigid peri phase and were oriented in the direction of tension. This is a clear indication that the bitumen's microstructure does affect homogeneity of the internal stress and strain fields and effectively causes non-homogeneous straining and even localisation in regions where stress concentrations are present. Furthermore, the recovery of the strain localised zones was studied. The strain localised zones completely recovered in the course of several hours.