Insights into the long-term corrosion behavior and inhibition mechanisms of calcium nitrite and N,N-dimethylethanolamine in reinforced concrete under chloride exposure
摘要
To improve the durability of reinforced concrete in chloride-rich environments, the corrosion inhibition performance and mechanisms of N,N-dimethylethanolamine (DMEA) and calcium nitrite (CN) were systematically investigated. Their effectiveness was evaluated in simulated concrete pore (SCP) solutions and in reinforced concrete specimens subjected to laboratory wet–dry cycles and marine splash zone exposure. Electrochemical measurements demonstrated that both inhibitors delayed chloride-induced de-passivation of steel, increased the critical chloride threshold, and enhanced passive film stability. Optimal dosages were identified as 1.5 wt% for DMEA and 3.0 wt% for CN. These dosages increased the charge-transfer resistance (Rct) from 8.34 × 103 Ω·cm2 (control) to 2.49 × 106 and 3.08 × 106 Ω·cm2, respectively, achieving high corrosion inhibition efficiencies of approximately 99.7%. Furthermore, the critical chloride threshold was increased from 0.17 to 0.34 M for 1.5% DMEA and 1.44 M for 3.0% CN, representing improvements of 1.0 and 7.4 times relative to the control. Surface analyses revealed that DMEA forms a thin, hydroxyl-rich organic layer through surface adsorption, whereas CN promotes the development of a dense, oxide-enriched passive film. Quantum chemical calculations and molecular dynamics simulations further elucidated their distinct inhibition mechanisms: DMEA strongly adsorbs via hydroxyl coordination, forming a physical barrier, while CN facilitates Fe2+ oxidation to Fe3+, thereby stabilizing the passive film. These findings advance the understanding of organic and inorganic corrosion inhibitors in reinforced concrete and provide both theoretical and experimental support for their rational application in aggressive environments.