Investigation of the Release and Self-Healing Properties of Calcium Alginate Capsules in Asphalt Concrete under Cyclic Compression Loading

Calcium alginate capsule encapsulating rejuvenators are a new approach to enhance the self-healing property of asphalt, but the release and self-healing properties of calcium alginate capsules in asphalt concrete under cyclic loading conditions are still unclear. In this research, calcium alginate capsule encapsulating sunflower oil as a repair agent was synthesized and the oil release ratios of the capsules in asphalt concrete after compression loading were determined through a Fourier transform infrared test (FTIR). Then, strength and fracture recovery tests and DSR test were conducted to evaluate the effects of the released oil on the healing levels and rheological properties of asphalt concrete. Finally, computed tomography (CT) scan and SEM tests were conducted to study the morphology of the capsules to analyze the oil release mechanism of calcium alginate capsules. The test results showed that with the increase of the compression loading cycles, more oil was released from the capsules and the self-healing level of the asphalt concrete increased obviously. In addition, the oil released from the capsules softened the asphalt, decreasing the complex modulus and increasing the phase angle of the asphalt. CT scan images showed that after compression loading and healing, the capsules deformed slightly but maintained their spherical shape, indicating that the capsules could release the oil from the cavities due to shrinking and deformation upon compression loading and restore their original shape after compression loading.