Investigation and Modelling of the Impact of Reinforcement Diameter in Concrete on Shapes of Impedance Spectra

Abstract

The impedance test results of the steel reinforcement of various diameters, which was passivated and corroded in concrete specimens, were analysed. The impedance plots clearly indicated the tendencies for spectra shapes of steel rebars to change depending on their diameters. A 3-dimensional model of steel-concrete system was developed to explain the observed effect. This system was composed of the identical electrical equivalent circuits connected in parallel. Each equivalent scheme was characteristic for a theoretical conductive path during the measurement, which was defined between a counter-electrode and the reinforcement. This model was used with the rectangular counter electrode to simulate the formation of impedance spectra characteristic for a single reinforcing bar with the concrete cover of any thickness, a variable diameter and a variable polarization area. The simulation modelling the impact of various reinforcement diameters verified the tendencies for impedance spectra of steel in concrete to change their shapes. The improved of fitting quality of the model spectra to the experimental ones were obtained by considering in that model the moisture content in concrete. IntroductionThe corrosive degradation of reinforced concrete structures [1-3] presents a real threat to their safe use and the reliability [4], [5]. Thus, the competence for assessing the corrosion risk properly and taking proper repair actions if necessary, is extremely important [6-10]. The application of the polarization techniques [11] and particularly the method of impedance spectroscopy for assessing the corrosion rate of the reinforcement in the reinforced concrete structures encounters considerable difficulties [12]. These problems are related to complex measurement conditions and the complicated testing system. The studies are carried out using the potentiostat in a three-electrode system, in which the structure reinforcement (made of long steel bars) serves as the working electrode, and the electrode of known and satisfactory reversible potential serves as the reference electrode. The counter-electrode is applied to the surface of the reinforced concrete element to make the reinforcement polarization possible. The counter-electrode along with the reference electrode in a single enclosure formed the so called measuring head. The use of the head created a situation considerably different from the laboratory conditions form the measurement in an electrochemical vessel in which the large counter electrode uniformly polarizes the small tested electrode of a simple geometry. Regarding the measurements on the reinforcement in the reinforced concrete elements, the area of the tested electrode was significantly larger than that of the counter electrode applied to concrete. This resulted in the very non-uniform polarization of steel rebars. Moreover, the polarization area of the reinforcement required for assessing the rate of the electrochemical processes was unknown. The additional counter electrode in a form of a guard ring reducing the...

A Two-Year Evaluation of Corrosion-Induced Damage to Hot Galvanized Reinforcing Steel B500SP in Chloride Contaminated Concrete

“…They include cathodic protection of reinforcement which provides permanent and controlled over time reduction of steel reinforcement potential in concrete to the level, at which metal exhibits resistance to corrosion. However, the use of the above method has to be preceded with the advanced diagnostic of corrosion employing such electrochemical methods as measurement of corrosion potential [ 17 ], measurement of the density of corrosion current [ 18 ]—the most common methods of linear polarization resistance (LPR) [ 19 ], electrochemical impedance spectroscopy (EIS) [ 20 ] and galvanostatic pulse (GP) method [ 21 ]. Those diagnostic methods are necessary for switching on and maintaining the direct current for cathodic protection throughout the whole service life of the structure.…”

Example of analysis of climatic data series with respect to the testing of reinforcement concrete corrosion in a climate chamber

“…Similarly, there is a need to expand the possibilities of a laboratory as well as real-time measuring. In-situ measurements of corrosion rate of reinforcement in concrete structures involve more advanced electrochemical methods, from Linear Polarization Resistance LPR [7], to advance measurements by means of Electrochemical Impedance Spectroscopy EIS [8,9]. For these tests, it is very important to have climate data related to the expected location of the structure.…”