E. Triki

Steel corrosion in concretes deteriorated by chlorides and sulphates: Electrochemical study using impedance spectrometry and ‘stepping down the current” method

Abstract This investigation deals with reinforced concrete specimens which were previously placed in aggressive aqueous solutions containing chlorides or sulphates. So, the steel rebars were corroded. The object of this study is to characterize the steel surface condition by using two electrochemical methods. The first method is the electrochemical impedance spectrometry (EIS), and the second one is the “stepping down the current” method (SDC). The results of the EIS method are in agreement with results which were previously published by other authors. It means that the shape of the Nyquist diagrams and the electrochemical parameters calculated from these diagrams characterize the rusting conditions of the rebars. The parameters calculated from the SDC results by using the Randles equivalent circuit, are also able to characterize the rusting condition of the rebars.

Comparing the steel-concrete interface state and its electrochemical impedance

Abstract The object of this investigation is to validate a model of electrical impedance of steel-concrete interface, which has been previously published. In this model, a part of the impedance is related with the products formed directly on steel. Another part of the impedance corresponds to the transition zone between steel and concrete. The third part corresponds to the inhomogeneity of the products formed at the interface. The validation of this model was obtained by testing reinforced concrete specimens made of three cements and aged in solutions containing chloride or sulphate. The results obtained with measuring electrochemical impedance were compared with the actual condition of steel.

Electrochemical methods for evaluating inhibitors of steel corrosion in concrete

Abstract Electrochemical methods were used to evaluate sodium phosphate and sodium nitrite as inhibitors for the corrosion of steel in saturated calcium hydroxide solution containing chloride ions. The studies included immersion, potentiodynamic, potentiostatic, and galvanostatic tests. The results obtained from these methods were in good agreement. They show that sodium nitrite is an anodic inhibitor which is not effective if its concentration is lower than that of the chloride ions. Sodium phosphate acts as an anodic inhibitor if its concentration is higher than 0·6 times the chloride concentration. It is totally effective when its concentration equals the chloride concentration.

Characterisation of steel/concrete interface by electrochemical impedance spectroscopy

Abstract Reinforced mortar specimens were placed in aggressive aqueous solutions and the electrochemical impedance of the reinforcing steel was measured after immersion for 73 weeks. At the end of the test, after removal of the mortar cover, the final condition of the reinforcing steel was examined visually. An equivalent electrical circuit of the interface impedance has been proposed: it includes dispersion terms for taking into account the inhomogeneity of the steel/concrete interface. The validity of the model has been assessed by comparing the results of visual examinations with data obtained by electrochemical impedance measurements which were processed according to the model.