Development of Smart Corrosion Inhibitors for Reinforced Concrete Structures Exposed to a Microbial Environment

Reinforced concrete deterioration due to acidification of the environment from microbial activity in view of steel performance is seldom reported and still a debate. An initial scrutiny of several inhibitors indicated methylene blue dye and trisodium-phosphate as the most promising candidates for mild steel protection in diluted H₂SO₄. Such compounds were combined together into two organic/inorganic hybrids composed of hydroxyapatite (HAP) or vaterite porous matrixes impregnated with methylene blue dye. The novel hybrid systems were characterized by means of scanning electron microscopy, X-ray diffraction, and Brunauer-Emmett-Teller analysis. The electrochemical response of steel specimens in a simulated environment containing loaded and empty HAP host was monitored by means of linear polarization resistance and electrochemical impedance spectroscopy. The results confirmed the inhibitive properties of the chosen compounds in acidic medium, pointing out a synergistic effect resulting from the release of the organic compound and the dissolution of the inorganic matrix.