Role of encapsulated corrosion inhibitor on the anti-corrosion performance of reinforcing steel in lightweight concrete

Abstract

This study aims to enhance the anti-corrosion performance of reinforcing steel in lightweight aggregate concrete (LAC) using lightweight aggregates (LWAs) to carry a corrosion inhibitor. To evaluate the effectiveness of the inhibitor firstly incorporated in the LWAs, the inhibition behaviors were monitored using electrochemical measurements and analyzed by microstructural characterization techniques after LAC was exposed to chloride solutions. The results indicate that the corrosion inhibitor (sodium monofluorophosphate (Na-MFP)) pre-adsorbed by LWAs under atmospheric condition significantly improved the corrosion resistance of the reinforcing steel in LAC. The open circuit potential (OCP) and linear polarization resistance (LRP) gradually increased and then remained stable, indicating that a compact and thick passivation film was formed on the steel bar after 28 d curing. Although the corrosion resistance of all samples decreased after immersing Cl− solution, the samples prepared with Na-MFP incorporated LWAs under atmospheric conditions showed the best anti-corrosion performance. The Na-MFP was released from LWAs and migrated to the reinforcing steel surface, generating a FePO4 passivation film. Furthermore, the released Na-MFP reacted with Ca2+ ions to form Ca3(PO4)2, acting as a protective barrier on the surface of reinforcing steel to improve corrosion resistance. However, the excessive precipitation of Ca3(PO4)2 between the LWAs and mortars led to the formation of cracks and accelerated the penetration of Cl−. Based on the interactions between reinforcing steel and corrosion inhibitor at the steel-mortar interface, the possible mechanisms of Na-MFP release and inhibition in chloride-contaminated solution were proposed.