The effect of layered double hydroxides on passivation and de-passivation of the steel reinforcement in simulated concrete pore solution

As promising carriers for corrosion-inhibiting anions, the influence of interlayers and intercalated anions in layered double hydroxides (LDHs) on passivation and de-passivation of the reinforcement remains unclear. This study examined the effects of LDHs with various interlayers (Ca 2 Al/Ca 2 Al 0.75 Fe 0.25 interlayers) and intercalated anions (NO 3 - /NO 2 - ) on corrosion performance of the reinforcement in simulated concrete pore solution (SCPs). During passivation process, NO 2 -LDHs enhanced the formation of Fe 3+ -rich passive film, whereas NO 3 -LDHs impaired passive film stability due to OH - adsorption and NO 3 - release. In de-passivation stage, NO 2 -LDHs provided superior inhibition effect by chloride adsorption and re-passivation, achieving higher critical chloride concentration and delayed corrosion initiation. Ca 2 Al 0.75 Fe 0.25 -NO 2 -LDHs exhibited outperformed inhibition effect owing to optimized NO 2 - release kinetics and strong passivation promotion. The results derived in this study provides the theoretical guide for the design of LDHs with excellent corrosion protection effect for reinforced concrete.