Self-healing capability and thixotropy of bituminous mastics

Fatigue resistance of bituminous materials is related to time-dependent phenomena, such as damage accumulation, hardening, viscoelasticity, thixotropy and healing. In bituminous mixtures, damage related to fatigue processes mainly involves bitumen and its combination with filler (i.e. mastic). Currently, there is no consolidated method for the determination of the fatigue endurance limit of bitumens that takes into account also the above-mentioned phenomena, while limited work has been done on mastics. To bridge this gap, the experimental investigation described in this paper provides a comparison between bitumens and corresponding mastics in terms of fatigue, self-healing and thixotropy. Long term aged materials were also taken into consideration in order to identify potential detrimental effects on self-healing due to oxidation phenomena, evaluating the possible inclusion of Reclaimed Asphalt (RA) for the production of bituminous mixtures. The data analysis was based on an innovative test method which had previously been implemented for bitumens and was carried out using a Dynamic Shear Rheometer (DSR). Moreover, the influence of morphological properties of filler on filler-bitumen interactions was assessed by means of a Scanning Electron Microscope (SEM). Results show that the above-mentioned analysis method is also suitable for analysing bituminous mastics and is able to identify the role of filler as well as the influence of ageing on the self-healing process of bituminous materials. The investigation confirms that a certain amount of aged bitumen added to a virgin bitumen/mastic is able to considerably improve the overall fatigue performance suggesting significant benefits when dealing with recycled mixtures including RA aggregates.