Corrosion behaviour of coated steel rebars in carbonated and chloride-contaminated alkali-activated fly ash mortar

The corrosion behaviour of hybrid organic-inorganic coatings applied on carbon steel embedded in carbonated ordinary Portland cement (OPC) and alkali-activated fly ash (AAFA) mortars and immersed in a 3 wt.% NaCl solution was evaluated using electrochemical methods. The sol-gel coatings were prepared by condensation and polymerization of TEOS/MPTS, TEOS/MTES, TMOS/MPTS and TMOS/MTES mixtures with a molar ratio of 1.0 and deposited by dip-coating on the carbon steel substrates. The coated steels embedded in AAFA mortar presented higher corrosion potential and lower corrosion current density values than those embedded in OPC mortar, indicating that the coatings were more efficient in preventing corrosion of the rebars in this environment. Hybrid coatings synthesized with TEOS/MTES and TMOS/MTES mixtures showed the longest permanence of steel in the passive state when covering rebars embedded in carbonated AAFA mortar. This enhancement of protection may be due to the denser and more compact structure of sol-gel coatings and their greater adhesion to the metallic surface. The study also considered uncoated steel specimens embedded in OPC and AAFA mortars for comparative purposes.