Coral waste-derived encapsulated lightweight aggregate for self-healing concrete: Towards enhanced sulfate resistance in marine environments

Self-healing concrete made with encapsulated lightweight aggregates shows considerable potential for enhancing concrete durability. However, self-healing concrete application is largely limited by aggregate selection, especially in marine environments. Coral waste from marine, characterized by high porosity, can serve as a kind of lightweight aggregate in concrete. This study developed a novel encapsulated coral aggregate (ECA) by vacuum impregnating a sodium silicate healing agent into coral aggregates and coating them with epoxy resin, which realizes the dual functions of lightweight aggregate and self-healing carrier. The healing agent release behavior from ECA was characterized, and the effect of ECA dosage on the crack healing efficiency, mechanical performance, and sulfate resistance of concrete was evaluated. The underlying mechanisms of self-healing and sulfate attack resistance were analyzed through characterizing the mineral and elemental composition of the healing products. Meanwhile, the electrochemical impedance spectroscopy (EIS) method was employed in order to explore the electrochemical recovery of cracks in concrete with different pre-cracking ages. The results demonstrated that ECAs not only served as lightweight aggregates but also effectively released the healing agent upon crack occurrence, promoting healing product formation. For concrete with an ECA replacement rate of 75%, the chloride ion migration coefficient was reduced by 49.9%. Given that sulfate attack is a primary durability threat in marine environments, the sulfate resistance of ECA-incorporated concrete was further evaluated to validate its suitability for such applications. The use of ECA improved the resistance of concrete to sulfate attack by mitigating damage from ion ingress and subsequent formation of expansive products. The findings of this study can provide a kind of self-healing concrete technology for marine engineering applications.