Corrosion Diagnostics Performed on Cores Drilled from Concrete Structures, Using the Laboratory Simulation of Temperature and Relative Humidity Impact  
[PERSON]  
1 Faculty of Civil Engineering, Silesian University of Technology, 5 Akademicka, 44-100 Gliwice, Poland; [EMAIL_ADDRESS]
methods can be employed: pressure extraction, vacuum extraction, or aqueous extraction from concrete powder can be prepared. In pore solutions [16; 17] simulating properties of concrete cover at different depths, chloride content is usually determined and pH measurements are taken.  
Measurements of corrosion potential and concrete resistivity can be classified into the second group of methods for corrosion diagnostics of concrete structures. Both those groups only provide the qualitative evaluation of corrosion risk for reinforcement in concrete. These methods can be used to evaluate the likelihood of corrosion on the basis of criteria recommended in the standards and literature. Results obtained from those tests can be presented in the form of clear colourful maps with contour lines [7; 18; 19].  
The third, final, group of the most advanced methods of corrosion diagnostics includes polarization methods, which have been adapted from the electrochemical laboratories to complex conditions of the in-situ tests. The expert practice shows that the following three methods are effective for the in-situ tests: linear polarization resistance (LPR) [20; 21], electrochemical impedance spectroscopy (EIS) [22; 23], and galvanostatic pulse (GP) [24; 25] methods. These methods are applied in a three-electrode arrangement, where steel rebar covered with concrete is used as the working electrode. Two other electrodes--reference and auxiliary--are placed in the measuring head on the concrete surface.  
Two aspects of the polarization methods are arguable. At first, such tests only determine the momentary corrosion rate at a specific temperature of concrete and at its specific moisture content. It means that a measurement taken during wet summer provides corrosion rate which differs from the measurements taken during dry winter. Unfortunately, none of these measurements can be regarded as mean or reliable. The second aspect refers to the range of polarization current which determines the area of reinforcement polarization [26; 27]. Knowing this area is significant for determining density of corrosion current in reinforcement. It should be underlined that transducers, that is, guard rings, have been used for many years. They are used to confine the propagation of polarization currents [28; 29; 30]. However, such results are disputable in case of polarization tests performed in the area of dense reinforcement, cross rebars and rebars going through a few layers. Drilling concrete cores with embedded rebar pieces from concrete structures seems to be more a better solution. The first proved tests of that type seem to be described in the paper [31]. The three-electrode system can be arranged under the laboratory conditions for cores drilled from the structure to perform polarization measurements by LPR, EIS, or GP methods which do not arise any interpretation doubts [32]. Additionally, the thermal and humidity conditions observed for the structures can be simulated [33]. In this way, the extremes, that is, the minimum and maximum densities of corrosion currents, which can occur during operation of the tested structure, can be determined.  
This paper presents the application possibilities of the diagnostics method based on cores drilled from the structure and improved by the authors, using the examples of reinforced concrete tanks for fresh water and cement storage silos. The practical application of this method is preceded by descriptions of theoretical foundations of observed physical and chemical phenomena, and by detailed technical information on the employed measuring systems.