Reinforced concrete is widely used for building materials and plays a significant role in economic development. However, the premature degradation of reinforced concrete structures due to the reinforcing steel corrosion has become a serious problem in modern society, which results in a huge economic loss. Under normal conditions, reinforcing steel in concrete can be protected from corrosion by forming a compact passive film on its surface in concrete pore solution with high alkalinity (pH 12.5-13.5). However, the passive film can be locally damaged and the localized corrosion of reinforcing steel takes place when pH and/or the chloride concentration at the steel/concrete interface reach the critical values for corrosion. Corrosion behaviour of metals and alloys in concrete solution has been investigated in presence and absence of inorganic and organic inhibitors. Usually carbon steel and steel rebars have been used. Sometimes galvanized steel and SS316L have been used. Organic inhibitors, inorganic inhibitors, and natural products have been used as inhibitors along with concrete admixture. Corrosion resistance of metals has been evaluated by weight loss method, electrochemical studies such as polarization study and AC impedance spectra. Galvanostatic pulse technique has also been employed. The protective film formed on the metal surface have been analyzed by SEM, FTIR spectroscopy, XPS, AFM and EDAX. The protective film consists of metal-inhibitor complex, calcium carbonate and calcium hydroxide. Experiments have been carried out at room temperature. Corrosion inhibitors fill up the pores and prevent the penetration chloride ion towards the metal surface. Passive films formed on the metal surface also increase the life time of concrete rebars.
Key words: corrosion inhibitors, concrete
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