Controlled release mechanism and inhibition performance of smart inhibitor LDH-NO₂ in the reinforced concrete structures

Reinforcement corrosion is one of the most serious problems limiting the durability of concrete structures. Corrosion inhibitors are used as admixtures in the fresh concrete to prolong the service life of the concrete structure, and calcium nitrite is the most extensively tested admixed inhibitor. However, the premature deactivation and overdose of conventional inhibitors limit their application, and one strategy to solve this problem is to use smart inhibitors with controlled release, long-term effects, and targeting performance. In this paper, a smart inhibitor of LDH-NO₂ was prepared based on the Zn‒Al layered double hydroxide as a shell and the nitrite ions as a core. The first principles calculation, physical detection techniques, immersion test, and electrochemical methods were performed to study the micro- and macro-controlled release mechanism and inhibition property of LDH-NO₂. The results show that: (1) The nitrites in LDH-NO₂ can release spontaneously in the chloride-contaminated or/and carbonated concrete. The release process reaches equilibrium in 1 h, repairing the corrosion damage of steel reinforcement in time. (2) The LDH-NO₂ is much more sensitive in the carbonated concrete than chloride-included concrete, reflected in the greater energy of ion-exchange reaction and the more stable product with thinner interlayer with stronger interlayer force. (3) In the simulated pore solution of chloride-contaminated and carbonated concrete, the corrosion inhibition efficiency of 5 g·L⁻¹ LDH-NO₂ on carbon steel reinforcement exceeds 99%, reducing the corrosion rate of carbon steel by one order of magnitude. (4) Compared with the conventional NaNO₂ inhibitor, LDH-NO₂ effectively prolongs the corrosion initiation time while decreasing the corrosion area of carbon steel reinforcement. (5) The corrosion inhibition performance of LDH-NO₂ is mainly due to the release of \textNO_2^ - from LDH rather than the corrosive ion adsorption on LDH. Therefore, the smart inhibitor of LDH-NO₂ shows excellent corrosion inhibition and a long-term effect in the reinforced concrete environment.