Innovative ZIF-8 modified ER@EC microcapsules: Enhancing slow-release and longevity for superior self-healing in cementitious materials

Abstract

Using microcapsules (MCs) for self-healing is one of the most cutting-edge strategies for repairing concrete cracks and improving the durability of reinforced concrete (RC) structures. MCs with ethyl cellulose (EC) as the shell material possess non-toxicity, high stability, and satisfactory encapsulation capacity. However, EC-based MCs suffer from the premature release of core materials due to their porous nature. This study synthesized the zeolitic imidazolate framework-8 (ZIF-8) and embedded it into the EC shell to enable a long-acting healing function of epoxy resin (ER) @ EC MCs. The morphology, thermal stability, chemical structure, release rates, and particle size of the ER@EC/ZIF-8 MCs were evaluated. The first and secondary self-healing performances of mortars with different MC dosages were determined. The results demonstrated the successful embedding of ZIF-8 into the MCs, with a 20 % dosage of ZIF-8 modification achieving the most sustained release. Furthermore, ER@EC/ZIF-8 MCs effectively reduced pores larger than 77.45 nm and decreased the overall porosity by 3.13 %. ZIF-8 modification enhanced strength healing, particularly the long-acting aspect, with the secondary healing rate peaking at 31.48 % at a 3 % dosage of modified MCs under dual 30 % f_c0 pre-damage. Meanwhile, the highest first healing rate (22.02 %) was also observed at a dosage of 3 % modified MCs under 30 % f_c0 pre-damage. Generally, the modified MCs showed a superior healing effect than the unmodified MCs. As a newly developed self-healing MC, the ER@EC/ZIF-8 MCs are expected to confer multifunctional properties to RC structures.