Bio‐based tannin‐loaded layered double hydroxides in epoxy coatings for smart corrosion protection of steel in underground infrastructure

Abstract Corrosion of steel in underground infrastructure threatens structural safety and drives high maintenance costs due to aggressive conditions such as chloride‐rich soils and stray currents. Conventional epoxy (EP) coatings offer limited durability, prompting the need for advanced solutions. This study introduces smart epoxy coatings incorporating Zn‐Al layered double hydroxides (LDHs) and tannic acid‐loaded LDH (LDH‐TA) to combine barrier enhancement with active, eco‐friendly inhibition. LDHs were synthesized, functionalized with TA, and integrated into epoxy matrices. Characterization was performed using X‐ray diffraction, Fourier‐transform infrared spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The EP‐LDH‐TA coating achieved a charge‐transfer resistance of 2.58 × 10 5 Ω·cm 2 and corrosion inhibition efficiency of 99.5%, outperforming neat epoxy (93.1%) and LDH‐only systems. Additional temperature‑ and pH‑dependent EIS tests revealed that LDH‑based coatings retain enhanced protection at elevated temperatures (40–60°C), and that their performance is strongly influenced by electrolyte chemistry. These results confirm a synergistic mechanism of chloride trapping and pH‐triggered inhibitor release, while also highlighting the environmental pH sensitivity of LDH‑ and TA‑based reinforcement. Overall, this work demonstrates a sustainable approach to stimuli‐responsive coatings for underground steel protection, offering significant benefits for durability and safety in deep underground engineering applications.