Electrochemical Impedance Spectroscropy Study on the Behavior of Reinforced Concrete Elements under Loading

Concrete is a material of porous nature that, when humidified, becomes an ionic conductor whose apparent conductivity depends on the ionic load (typically based on OH−, Ca2+, Na+, and K+) and the amount of available free water. Under conditions of partial pore-saturation, the amount of free water can be modulated by an external load, which leads to observable changes in electrical properties such as conductivity and capacitance. Moreover, metallic reinforcements, either as bars or fibers, represent an additional parallel conduction path but of an electronic nature in this case. The free water develops a double-layer capacitance structure at the metallic interfaces, with associated charge-transfer resistance, representing an additional contribution to the capacitive behavior that can be modulated with an external load. The dependence that the electrical and/or ionic conducting properties of concrete and reinforced concrete elements have on the available free water makes them suitable for transductors in various sensing and self-sensing applications discussed in the text.