Enhanced chloride transport resistance and corrosion protection of reinforced concrete by NO2-LDHs@MMT: Electrochemical evaluation and coupled modeling

Chloride-induced corrosion of reinforcing steel is a major cause of durability deterioration in reinforced concrete, whereas the efficiency of layered double hydroxides (LDHs) is often limited by agglomeration in cementitious systems. This study investigated a NO 2 -intercalated LDH/montmorillonite composite (NO 2 -LDHs@MMT) as a multifunctional additive for improving chloride resistance and corrosion protection, with NO 2 -LDHs as a reference. Rapid chloride migration (RCM), open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and Tafel polarization were combined with a coupled chloride transport-corrosion model. Both additives reduced chloride migration, but NO 2 -LDHs@MMT showed the stronger effect. At a dosage of 2 wt% by mass of binder, the chloride migration coefficient decreased from 14.3 × 10 −12 to 8.3 × 10 −12 m 2 /s, corresponding to an approximately 41.95% reduction. Under electrically accelerated chloride ingress, the 2 wt% NO 2 -LDHs@MMT specimen maintained a more positive OCP (-0.279 V vs. SCE at 162 h), a much higher charge-transfer resistance (3010 kΩ·cm 2 ), and a markedly lower corrosion current density (0.0312 × 10 −5 A·cm −2 ) than the blank specimen, yielding an inhibition efficiency of 99.5%. The coupled model reproduced the measured corrosion current with a measured-to-simulated i corr ratio of 0.918–0.970 and predicted lower chloride accumulation, thinner corrosion products, and less damage during 300 d exposure. The improved performance of NO 2 -LDHs@MMT is associated with chloride capture, better LDH dispersion, and a larger effective interaction interface provided by MMT.