Electrochemical performance of steel in cement extract and bulk matrix properties of cement paste in the presence of Pluronic 123 micelles

The influence of Pluronic P123 (PEO₂₀-PPO₇₀-PEO₂₀) non-stabilized micelles (of 10 nm size) on the corrosion behavior of low-carbon steel in cement extract was studied, using electrochemical impedance spectroscopy (EIS) and potentio-dynamic polarization (PDP). Mercury intrusion porosimetry (MIP) was employed to derive the impact of admixed P123 micelles on porosity and pore-size distribution of cement paste. As far as steel corrosion resistance is concerned, a positive effect was observed, initially denoted to the presence of the polymer itself, rather than the presence of micelles. Further, the P123 micelles were found to result in increased corrosion resistance in the presence of 1 % and 3.5 % NaCl in the alkaline environment of cement extract. There was no significant influence on porosity and pore size distribution of the admixed in cement paste P123 micelles. The observed phenomena are related to self-assembly of the micelles only within higher ionic strength and the presence of chloride, in which case the critical micelle concentration is reduced. At micelles concentration of 0.024 g/l for the chloride-free cement extract (and the solid cement paste specimens, respectively), the medium actually contain unimers that have minimal impact on electrochemical performance and/or microstructural properties. In contrast, with increased ionic strength of the medium (1?3.5 % NaCl and altered ion concentrations resulting from the anodic/cathodic reactions within steel corrosion), the positive effect of 0.024 g/l micelles (and higher of 0.072 g/l) is more pronounced, i.e., increased corrosion resistance and anodic control with external polarization was observed.