Performance of lanthanum 4-hydroxycinnamate in a polyurethane coating in simulated seawater - Exposed cement solution

Ingress of chloride ions through the pore network of concrete towards embedded streel reinforcement can result in pitting corrosion and, if left unchecked, to reinforcement corrosion. Considering the cost of repairing and replacing damaged concrete structures in coastal zones, rebar coatings incorporating corrosion inhibitors may provide a cost-effective method to significantly extend service life. Rare earth compound-based corrosion inhibitors, such as lanthanum 4-hydroxycinnamate (La(4OHCin)3), have demonstrated effective corrosion inhibition on mild steels under neutral pH conditions. To date, limited research has investigated the performance of La(4OHCin)3 within coatings under high pH conditions, such as those found in reinforced concrete in seawater-exposed environments. In this preliminary study, the inhibitor La(4OHCin)3 was incorporated into a polyurethane-based coating and painted over the polished cross section of mild steel (AS1020) round bar specimens mounted in epoxy. A 5 mm artificial scribe was made on each sample and subsequently immersed in simulated seawater-exposed cement pore solution (0.6 M sodium chloride and saturated calcium hydroxide) for several days. Time lapse optical microscopy (showing the progression of corrosion), polarization resistance measurements (monitoring the electrochemical behaviour) and surface characterization with SEM/EDX were conducted to compare the relative performance of the REM-based inhibitor with the uninhibited polyurethane control coating. Results demonstrate that the La(4OHCin)3 incorporated into a polyurethane-based coating provides effective corrosion inhibition in the high pH and high salt environment of the simulated exposed cement solution.