Corrosion inhibition mechanism of phosphates for early-age reinforced mortar in the presence of chlorides

A study was performed on the corrosion-inhibition mechanism of three phosphate compounds (sodium monofluorophosphate, disodium hydrogen phosphate and trisodium phosphate) for steel rebars embedded in ordinary Portland cement (OPC) mortar exposed to 3% NaCl solutions. The corrosion inhibitors were deployed in two different ways: by migration after the curing period, through the immersion of mortar specimens in aqueous solutions containing the soluble phosphates; and by initial admixture of the phosphate powders in the OPC mortar. The tested specimens were studied using electrochemical corrosion potential and linear polarisation resistance for 70 days of experimentation. A correlation was found between the phosphate content of the specimens (by migration or admixture) and the steel corrosion rate. The results indicate that all the phosphates have the ability to inhibit steel corrosion in mortar.