Self-healing properties of seawater sea-sand strain-hardening cementitious composites (SHCC)

Seawater sea-sand concrete reinforced with non-corrosive reinforcements is attractive for marine infrastructures, while self-healing of cracks can enhance the longevity of concrete structures under harsh marine environments.However, current knowledge on the self-healing properties of Seawater Sea-sand Strain-Hardening Cementitious Composites (SS-SHCC) remains limited.This study aims to address this gap by investigating the self-healing mechanism and multi-scale healing performance of SS-SHCC.Firstly, the self-healing mechanism of SS-SHCC was explored at a single crack level.The effects of binder composition, initial crack width, and exposed conditions (involving seawater wet-dry cycling and immersion) on the self-healing behavior of the matrix were explored.Crack width was monitored throughout the healing period, and the self-healing products were characterized using X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy.Subsequently, the multi-scale self-healing performance of the SS-SHCC was evaluated across four simulated marine environments.Surface crack healing and resonant frequency measurements were assessed during self-healing, while permeability and mechanical performance tests were conducted after self-healing.The findings revealed that the primary self-healing products in marine environments consisted of portlandite, brucite, aragonite, and calcite.The self-healing performance was primarily governed by the availability of Ca and OH ions precipitating from the matrix.The presence of seawater in marine environments is pivotal for the self-healing efficacy of SS-SHCC, and the self-healing of SS-SHCC in the air zone was less pronounced.With the exception of the air zone, SS-SHCC's normalized resonant frequency recovered to more than 75% of its initial value, while permeability stayed below 110 -10 m/s, preserving outstanding mechanical properties.These findings provide valuable insights for the design and application of SS-SHCC, contributing to enhanced durability and longevity of marine infrastructures.