Effect of Na3PO4 inhibitor on chloride diffusion in mortar

The penetration of chloride ions by diffusion has become among the most important factors that lead to concrete reinforcement deterioration. To solve the corrosion problem and achieve the expected service life of reinforced concrete structures, many procedures can be employed such as the use of corrosion inhibitors. In this paper a phosphate based inhibitor (Na3PO4·12H2O) has been used to study its effectiveness against corrosion and its influence on chloride ions diffusion. This study has been conducted in steady-state conditions using a specific diffusion cell. This simple and effective technique was complemented by the use of a non-destructive method for measuring the concentrations of free chloride ions, diffused through the mortar containing or not phosphate inhibitor, which is the specific chloride electrode (ORION 96-17). The Inhibitor effect, the period and the chloride corrosion threshold of steel reinforcement has been followed using electrochemical techniques. Characterization methods were employed in order to study the behavior of the mortar in absence and presence of phosphate inhibitor. From these methods, it was possible to calculate the evolution of chloride diffusivity over the whole range of chloride concentrations. Results show that the addition of phosphate inhibitor in mortar can reduce significantly the corrosion rate of steel reinforcement in chloride solution, and also increases the critical period of pitting initiation from 30 to 100 days. In these conditions, the calculated chloride diffusion coefficient was estimated at 0.103 × 10−11 m2/s, value obviously lower than that obtained in the case of the mortar without inhibitor (0.22 × 10−11 m2/s), during the same period. Thus it can be concluded that the presence of this phosphate inhibitor in mortar reduces the chloride diffusion rate.