Research On The Thermally Activated Self-healing Properties Of Asphalt And Asphalt Mixtures

Asphalt binder is a self-healing material that has the potential to heal faster with the increasing temperature.It is feasible to heal the cracks in asphalt concrete pavement through heating.In this paper,the thermal self-healing properties of asphalt,asphalt mastic and asphalt mixtures were studied by Dynamic Shear Rheometer(DSR),Bending Beam Rheometer(BBR)and Dynamic Mechanical Analyzer(DMA).First,the flow behaviors of asphalt binders were studied by DSR viscosity-frequency sweep test to find out their potential optimal temperatures,and the healing rates of the asphalt binders at different temperatures were measured by fatigue-healing-re-fatigue to confirm the optimum healing temperature of each asphalt binder.Moreover,the healing time required for the complete healing of asphalt binders was studied.It was found that both the fresh and the aged 70# and 90# penetration grade asphalt showed a near Newtonian fluid state binder at their specific softening point temperature where the asphalt binders exhibited the best self-healing properties to heal fatigue damage.And ageing increased the optimal heating temperatures of asphalt binders.SBS modified asphalt obtained full healing at a much lower temperature than its softening point.The experimental results also showed that both 70# and 90# penetration grade asphalt could obtain full recovery of the fatigue damage after heating at their softening point temperatures for 20 minutes.This heating time is in accordance with the healing time required for complete healing of the asphalt binder calculated from the Wool and O'connor models.In addition,three-point bending fracture-healing-refracture tests were conducted using BBR and the strength recovery rate was used as the healing index to study the self healing efficiencies of asphalt mastics(70# asphalt mastic,90# asphalt mortar and SBS modified asphalt mastic)at different heating temperatures and time.The self healing mechanisms of asphalt binders were analyzed accordingly.The results showed that 70# asphalt mastic and 90# asphalt mortar showed the best self-healing performance at slightly higher temperatures than the softening points of asphalt binders,and SBS modified asphalt mastic demonstrated a good healing performance at a lower temperature than the softening point of the binder.The self healing mechanisms of base asphalt binder and SBS modified binder are different.the healing of base asphalt mastic is due to the viscous flow of asphalt and the diffusion of asphalt molecules at crack surfaces,while the healing of SBS modified asphalt mastic is a combined result of asphalt flow and the elastic recovery of SBS networks.Finally,there point bending tests were conducted on asphalt concrete beams using DMA and the fracture energy recovery after heating was used as the healing index to evaluate the self-healing properties of asphalt concrete.It was found that the asphalt concrete showed similar self healing properties to the asphalt mastic studied.Both 70# asphalt mixture and 90# asphalt mixture obtained the optimal self healing properties at temperatures slightly higher than the softening points of the binders,while SBS modified asphalt mixture had achieved the best healing performance at lower temperature than the softening point of the binder.It required much longer heating time for asphalt mixture to heal the cracks,because the filler and sand within the mixture were hindrances to the flow of the binder.