Efficient preparation and characterization of calcium alginate-attapulgite composite capsules for asphalt self-healing

Calcium alginate capsules encapsulating rejuvenator are a promising self-healing technology for asphalt pavement, but the high cost and low preparation efficiency of the capsules cannot meet the requirements of application. This research proposed an efficient method for preparing low-cost calcium alginate capsules using industrial calcium sodium and self-developed reaction kettle. To enhance the strength and assure the survival of the capsules in asphalt mixture, attapulgite was incorporated in different proportions to form composite shell capsules, and their microstructure, thermal stability, mechanical strength, and release behavior of the rejuvenator were investigated. It was found that the composite shell capsules prepared with 2.0 wt% industrial sodium alginate solution and industrial sodium alginate to attapulgite ratio 1:1 had clear multi-cavity structure, high thermal stability, and sufficient mechanical strength for their use in asphalt mixture. The multi-cavity composite shell capsules within asphalt mixture can gradually release the rejuvenator inside in wheel tracking test. The test result showed that the capsules can release 82.67% of the rejuvenator and significantly soften the binder when they suffered 115,200 cycles of compression loading (equivalent to 7 years traffic loading on capsules within a medium traffic grade pavement), indicating that the rapid prepared composite capsules can release rejuvenator to soften asphalt binder and enhance the crack-healing property of asphalt pavement during the service life. (c) 2021 Elsevier Ltd. All rights reserved.