Heat-Induced Healing Potential of Bituminous Mixtures: Role of Mixture Parameters and Heating Method

Healing of cracked bituminous mixes/layers by heating them is considered an effective pavement maintenance strategy in recent times. This study aims to investigate the heat-induced healing ability of cracked bituminous mix specimens prepared with dense and gap gradations and using both unmodified and modified binders. Damaged mix specimens were healed by heating them to different temperatures (60°C, 80°C, 100°C, and 120°C) using induction as well as microwave methods of heating, and optimum heating temperatures were identified for different mixes. The influence of different binder parameters, such as surface free energy, saturates, aromatics, resins, and asphaltenes (SARA) fractions, and binder film thickness on the healing capacity of different mixes heated by different methods, has been demonstrated in this study. Gap-graded mixtures had better healing characteristics due to their larger binder volumes. Empirical models were developed for the estimation of the healing capacity of different mixes (with different aggregate gradations, binder type, and binder contents) for both microwave (R2=0.93 and Se/Sy=0.28) and induction (R2=0.92 and Se/Sy=0.26) methods of heating. A model was also proposed to obtain the optimum heating temperature as a function of viscosity and film thickness of the binder (R2=0.70 and Se/Sy=0.58). In both the heating methods, recovery of the indirect tensile strength (ITS) of different mixes (range of 0.3 to 0.8) varied widely with the gradation and binder of the mix. However, for a given mix and set of heating conditions, the microwave heating method resulted in better healing compared with the induction method due to the greater uniformity of heating and longer retention of heat. This, indeed, could be ascribed to the microwave susceptibility of the aggregates possessing significant dielectric properties, i.e., a dielectric constant of 5.69 and a loss factor of 0.46. The study presents the necessary inputs and understanding to appreciate the influence of various mixture and heating method variables on the resulting healing of the mixes.