(398f) The Impact of the Activity Coefficient on the Effectiveness of Corrosion Inhibitors in Steel Reinforced Concrete Systems

Metal surface corrosion poses a significant challenge the world over, but this is especially true in steel reinforced concrete structures. To protect the structural integrity of the system, corrosion inhibitors are often used as they can create protective films on the metal surface which mitigate attack from harmful chloride ions. The performance of corrosion inhibitors depends on several factors, one of which is how effectively they are transported within these systems to the surface of the metal. One way to characterize such movement in these complex systems, which contain a variety of ions, is through the concept of activity, which provides an effective concentration of the species in the system.

At low ionic strengths, a Debye-Hückel approach is sufficient to model the activity coefficient of electrolytes, but this fails at more modest ionic strengths and beyond (which are often found in structurally reinforced concrete). Therefore, more sophisticated models, such as the Pitzer approach, which accounts for both long-range electrostatic effects and short-range specific ion interactions, are required.

Our previous work [1] showed that cationic species for the same anionic inhibitor, which are not directly involved in the inhibition mechanism on the surface of the metal, changes the electronic environment of the system. This, in turn, impacts the inhibition efficiency of the anionic species, which is evidenced by a change in the activity of both the anionic inhibitor and the chloride ions.

Our current work looks to explore more deeply the validity of the relationships between inhibition efficiency, ionic strength, and activity coefficient, aided by the Pitzer equation.

[1] A. Mohamed, D. P. Visco, Jr. and D. M. Bastidas, “Effect of cations on the activity coefficient of NO2–/NO3– corrosion inhibitors in simulated concrete pore solution: An electrochemical thermodynamics study”, Corrosion Science, 206, 110476 (2022).