Laboratory testing of self-healing microcapsules in asphalt mixtures prepared with recycled asphalt shingles

Self-healing products such as microcapsules filled with an asphalt rejuvenator present an emerging technology that would allow asphalt mixtures to resist cracking damage caused by vehicular and environmental loading. The objective of this study was to characterize laboratory-prepared microcapsules in order to evaluate thermal stability as well as the self-healing effectiveness of the microcapsules in asphalt mixtures. A three-point bending test was used to evaluate the healing efficiency and stiffness recovery in asphalt mixtures under two healing conditions: room temperature and high temperature. An optical microscope was used to quantify the healing progress of cracked specimens as a function of time. Based on microscopic characterization, it was observed that the produced microcapsules had adequate thermal stability because the microcapsules showed no sign of breakage when exposed to high temperature. An analysis of microscopic images revealed a reduction in the size of the cracks for both healing conditions for a period from 0 to 6 days. A lower healing efficiency was observed for the mixture with microcapsules compared with the control because not all microcapsules have broken during the test and are designed to break over time and not all at once. Results also showed that there was a recovery in the stiffness of the mixtures because the healed stiffness was greater than the damaged stiffness but less than the undamaged stiffness. A greater stiffness recovery was observed at high temperature, which could be explained by binder aging during the 5-day conditioning period