Electrochemical Impedance Spectroscopy as a Practical Tool for Monitoring the Carbonation Process on Reinforced Concrete Structures

Carbonation results in a decrease in the pH of the cementation matrix when CO₂(g) from the environment diffused into the concrete structure that can cause the loss of passivity condition on the reinforcing steel surface and leads to early failure of concrete by corrosion attack. There are several monitoring techniques to evaluate the process of lowering the pH in the concrete, named carbonation depth progress. In this research, an electrochemical AC impedance spectroscopy (EIS) technique has been used as an effective laboratory tool for monitoring the evolution of the carbonation progress. A comparison with the traditional phenolphthalein colorimetric technique was also discussed here. Particularly, monitoring is achieved by measuring the change in electrical resistance (R_po) and capacitance (C_po) of the concrete bulk, which is obtained from the semicircle at high-frequency region of a typical EIS diagram. According to the EIS results, carbonation progress was observed by a significant increase in the diameter of the semicircle, thus demonstrating the increase in resistivity of ions transmission due to blockade of pores by precipitation of CaCO₃ compounds. Furthermore, it was possible to predict the specific time at which the carbonation front reaches the steel-rebar interface at low frequency region and possibly starting a considerable corrosion attack. Finally, the results suggested that EIS technique could be considered a practical tool for evaluating the carbonation progress of reinforced concrete structures without causing structural damage, in addition to the sensitivity of this technique with sufficient accuracy to predict the activation of the reinforcing steel.