Effect of chloride ingress on self-healing recovery of smart cementitious composite incorporating crystalline admixture and MgO expansive agent

Highlights: • Crack closure under wet/dry cycles in chloride solution is higher than the one in distilled water. • Element analysis shows that calcium is vital for crack healing either in water or chloride solution. • AFm is consumed by chloride ion to form Fs, and Fs were decomposed to AH₃ by carbonation. • Soluble reactive silica reacts with calcium hydrate to form C-S-H gel to heal concrete cracks. • Expansion of magnesium hydroxide facilitates crack self-healing by interconnected network. In this study, the effect of chloride environment containing various concentrations of chloride ion (Cl⁻) on self-healing performance of pre-cracked cementitious composite containing crystalline admixture (CA) and MgO expansive agent (MEA) was investigated under wet-dry cycles in chloride solutions. The results revealed that the Cl⁻ changed the mineralogy of self-healing products, and consequently, affected the crack closure ratio and mechanical strength recovery. When self-healing occurred in distilled water, a large amount of ettringite (AFt) were detected, whereas in Cl⁻ solution, monosulfate (AFm) was consumed by Cl⁻ to form Friedel's salt (Fs), and then the Fs was decomposed to Al(OH)₃(AH₃) due to carbonation. During the multiphase conversion process, hydroxide (OH⁻) was released into crack solution, therefore the dissolved carbon dioxide (CO₂) concentration was increased. The carbonation of the crystals formed in cracks was accelerated with the volume expansion, which achieved rapid crack sealing but contributed little to the mechanical performance recovery.