Calcium alginate capsules containing rejuvenators represent a promising method for asphalt concrete premaintenance, but their healing capacities under lower temperature conditions are still unknown. This paper investigated the healing performance of asphalt concrete containing calcium alginate capsules at low service temperatures. The Ca-alginate capsules were synthesized, and their morphology, compressive strength, thermal resistance, and relative oil content were evaluated. Besides, evaluations for the healing of asphalt concrete and the rejuvenator-release ratio of the capsules were determined via fracture-healing-refracture testing and Fourier-transform infrared spectrum experiments. Meanwhile, the glass transition temperature and rheological property of asphalt binder after compressive loading under different temperatures were explored via a differential scanning calorimeter and dynamic shear rheometer. The results showed that the capsules had good thermal resistance and mechanical strength. The capsules released less oil under −15, −10, and −5 ℃ than at 20 ℃, and the healing ratios of the asphalt concrete with the capsules at −15, −10, and −5 ℃ were obviously lower than that at 20 ℃. The released rejuvenator from the capsules could decrease the complex modulus and glass transition temperature of the asphalt binder. When compared with low service temperatures, the asphalt binder containing the capsules and serving at a high temperature has a better softening effect and low-temperature performance due to more oil being released.

Calcium alginate capsules encapsulating rejuvenator are a promising self-healing technology for asphalt pavement, but the effects of different healing agents on the self-healing performance of asphalt concrete has not been considered. In view of this, this paper aimed at exploring the effects of calcium alginate capsules containing different healing agents on the self-healing properties of asphalt concrete. Three types of capsules with sunflower oil, waste cooking oil and commercial rejuvenator were fabricated via the orifice-coagulation bath method and the interior structure, mechanical strength, thermal stability and oil content of the prepared capsules were characterized. The healing levels of asphalt mixtures with different capsules under different loading cycles and stress levels were evaluated. Furthermore, the saturates, aromatics, resins and asphaltenes (SARA) fractions and rheological property of extracted asphalt binder within test beams with different capsules after different loading conditions were assessed. The results indicated that all the three types of capsules meet the mechanical and thermal requirement of mixing and compaction of asphalt mixtures. The healing levels of test beams containing vegetable oil capsules were higher than that of waste cooking oil capsules and industrial rejuvenator capsules. The strength recovery ratio and fracture energy recovery ratio of test beams with vegetable oil capsules reached 82.8% and 96.6%, respectively, after 20,000 cycles of compressive loading at 1.4 MPa. The fracture energy recovery ratio of the waste cooking oil capsules also reached as high as 90%, indicating that waste cooking oil can be used as the healing agent of calcium alginate capsules to improve the self-healing property of asphalt mixture. This work provides a significant guide for the selection of healing agent for self-healing capsules in the future.

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In asphalt pavement thermal regeneration, incorporation of regenerant can restore the properties of aged SBS modified asphalt, but the effect of regenerant on the recovery of aged asphalt and the dosage of regenerant are not clear. In this study, experiments are carried to determine the effect of regenerant on the performance of aged SBS modified asphalt and the appropriate dose. Accelerated aging test is conducted by rolling thin film oven test (RTFOT) at different times. Then, different doses of regenerant (2 %, 4 %, 6 %, 8 %, 10 %, 12 %) are added to the specimens before and after aging, and test its technical indexes such as penetration, softening point and ductility to analyze the effect of regenerant on the properties of aged asphalt. The results show that: with the increase of the amount of regenerating agent, the aging asphalt performance indexes are restored, the softening point of regenerated asphalt is reduced, and the ductility and needle penetration are increased. Based on the analysis of the relationship between the aging time of SBS modified asphalt and the amount of regenerant, interpolation fitting is carried out to obtain the formula for the best amount of regenerant, so as to determine the best regenerant dosage for aged asphalt mixes in actual engineering applications.