Self-healing of steel corrosion in a model alkaline medium: electrochemical response and surface analysis

Abstract

The application of polymeric nano-particles for corrosion control in reinforced cement-based systems was studied. As an initial investigation, steel electrodes (St37) were tested in modified cement extract (CE), which is a model pore solution of pH 12.9 and chemical composition: 201 mg/l Ca; 3.85 mg/l K; 1.33 mg/l Na; 4 mg/l Al, Fe < 1 mg/l. Corrosion initiating factor was 5% NaCl. PEO 113 -b-PS 780 vesicles at 0.0024 wt.% in the CE were employed. These are nano sacs of 220 nm, enclosing a volume with a thin membrane, thus able to effectively entrap water-soluble compounds. Ion binding (bulk liquid medium), steel surface adsorption and/or participation in oxide layers formation were the expected mechanisms of particles' involvement. Both "empty" and "Ca-containing" vesicles were studied to evaluate "barrier" effects only vs. self-healing mechanisms. Increased steel corrosion resistance in the presence of both vesicle types was observed, however, it was more pronounced when Ca-containing ones were involved. Cyclic voltammetry and X-ray photoelectron spectroscopy analysis substantiate the self-healing phenomena, through direct evidence of pitting formation and propagation and consecutive healing (and no further pit formation) when Ca-containing vesicles are present.