# Electrochemical Diagnostics of Sprayed Fiber-Reinforced Concrete Corrosion
## 3 Diagnostic Methods for Assessing the Degree of Reinforcement Corrosion  
Shotcrete tests are usually related to mechanical parameters, such as compressive strength determined on specimens cut from the test slab, bending strength tested on specimen bars, shrinkage measured after minimum 90 days, adhesion to concrete, as well as freeze-thaw durability, water absorption, and waterproofing of concrete. The tests are conducted in accordance with the applicable standards [31; 32; 33; 34; 35; 36; 37]. The tests mentioned above do not include corrosion diagnostics of the primary reinforcement. However, from a structural integrity standpoint, assessment of the degree of corrosion of the reinforcement, and forecast of the advancement of corrosion, is crucial. It is particularly important for industrial and civil engineering structures, which are usually operated in more aggressive environments and are frequently built with the use of shotcreting. The available methods of reinforcement corrosion diagnostics for structures in use include electrochemical tests [38; 39; 40; 41; 42]. One such method is the semi-nondestructive method of measuring polarization resistance with the use of a galvanostatic pulse [43]. This method is based on the electrochemical corrosion of concrete reinforcement. Concrete has a porous structure, with the pores filled with alkaline liquid (a type of electrolyte through which ions can flow), while the steel rebar serves as the electrode placed in the electrolyte (conducting electrons). With the use of appropriate equipment (e.g., GP-5000 GalvaPulseTM), this makes it possible to measure some electrical parameters that allow indirect estimation of the reinforcement corrosion progress in concrete. The electrical parameters are: reinforcement stationary potential (E\({}_{\text{st}}\)), measured on the concrete surface; concrete cover resistivity (\(\Theta\)); and the corrosion current density (\(i_{\text{cor}}\)). Measurements of the reinforcement stationary potential and the concrete cover resistivity are the basic measurements, which allow only for areas where conditions for corrosion are more favorable to be pointed out. These measurements are not very accurate. More reliable are so-called advanced measurements, consisting of additional corrosion current density measurements, so we can estimate the reinforcement corrosion activity and forecast its rate. In order to take the measurement, it is necessary to connect the diagnosed reinforcement with the measurement kit, which includes, among others, a gauge (minicomputer) and a reference electrode. Figure 5 shows a diagram of the connection of the GP-5000 GalvaPulseTM and the diagnosed rebar. The generated electric impulse then polarizes the reinforcement and the relevant electric parameters are measured, i.e., the stationary potential of the reinforcement, the resistivity of the concrete cover, and the corrosion current density. The obtained values are referenced to the threshold values (Table 2)to determine the areas with a higher probability of corrosion, and to estimate the corrosive activity of the diagnosed reinforcement and forecast the corrosion rate. It should be noted that other corrosion measuring devices have different reference scales, and the results cannot be directly compared. The paper presents the results of the studies conducted with the use of the method described above (partially discussed in Reference [19]) which made it possible to determine the differences in the corrosion rates of the primary reinforcement in plain concrete and fiber-reinforced concrete with randomly dispersed steel fibers. In order to simulate the impact of an corrosive environment and trigger the corrosion process on the reinforcement, the specimens were exposed to freezing cycles in 3% NaCl solution, which initiated the so-called chloride corrosion.