Synthesis and characterization of calcium alginate-attapulgite composite capsules for long term asphalt self-healing

Calcium alginate capsules can gradually release the healing agent inside without rupture under cyclic traffic loading and are a promising self-healing technology for asphalt pavement. However, they have a low strength and tend to release the healing agent too fast. To enhance the strength of calcium alginate capsules and prevent them from releasing healing agent prematurely, calcium alginate-attapulgite composite capsules were synthesized with different synthesis parameters and their physical properties, morphological characteristics, release and healing behaviors were studied respectively. It was found that the incorporation of attapulgite improved the strength of calcium alginate capsules and could prevent the capsules from leaking healing agent during the drying process. The incorporation of attapulgite also slowed down the healing agent (sunflower oil) release speed of the calcium alginate capsules. Calcium alginate-attapulgite composite capsules can release 55.2% of the oil inside after 4 years of service within a medium traffic grade pavement, providing asphalt mixture with the ability to release the oil gradually to suit the cracking process of asphalt pavement. The released oil from the calcium alginate-attapulgite composite capsules improved the self-healing property of asphalt mixture and the capsules maintained their original spherical shape after releasing most of the oil inside. (C) 2020 Elsevier Ltd. All rights reserved.