# Electrochemical Diagnostics of Sprayed Fiber-Reinforced Concrete Corrosion
## Laboratory Tests
### Results and Analysis of the Tests  
The specimens tested for the probability of surface corrosion and the corrosion activity of the reinforcement provided a large number of results, since measurements were taken for three parameters (i\({}_{\text{cor}}\), E\({}_{\text{st}}\), \(\Theta\)) on four measurement points for each of the 12 specimens (two for each rod) in two stages (before and after freeze-thaw cycles). For the purpose of analyzing the results for each rod, a single representative measurement point was selected in which the corrosion current density (i.e., the most reliable parameter) was the highest after stage II measurements had been completed. The obtained results were referenced to the threshold criterion values provided in Table 2.  
The measurements of the corrosion current density taken on the first stage of tests for all rods of A1 and A2 specimens showed that the corrosion current density value did not exceed i\({}_{\text{cor}}\) = 2 \(\mu\)A/cm\({}^{2}\) for any of the measurement points (Table 3, Figure 8), which, according to the criteria adopted herein (Table 2) indicated a \"negligible corrosion activity.\" Comparative analysis of the results obtained on the second stage of the tests (after 120 freeze-thaw cycles in 3% NaCl solution) showed that in both A1 and A2 specimens, the density of the corrosion current increased, whereby in A1 specimens the density exceeded 5 \(\mu\)A/cm\({}^{2}\) (i\({}_{\text{cor}}\) = 5.5-9.9 \(\mu\)A/cm\({}^{2}\)) on all analyzed points, indicating \"moderate corrosion activity,\" whereas in A2 specimens the density did not exceed i\({}_{\text{cor}}\) = 5 \(\mu\)A/cm\({}^{2}\) on five measurement points, and for the remaining seven points, it fell within the range of i\({}_{\text{cor}}\) = 5.4-6.9 \(\mu\)A/cm\({}^{2}\), i.e., lower than in A1 specimens. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Corsion Current Density**} & \multicolumn{4}{c}{**Reinforcement Stationary**} & \multicolumn{4}{c}{**Concrete Cover Resistivity**} \\ \cline{2-13}
**Rod no. ** & \multicolumn{4}{c}{**A1**} & \multicolumn{4}{c}{**A2**} & \multicolumn{4}{c}{**A1**} & \multicolumn{4}{c}{**A2**} & \multicolumn{4}{c}{**A1**} & \multicolumn{4}{c}{**A2**} \\ \hline  & e. I & e. II & e. I & e. II & e. I & e. II & e. I & e. II & e. I & e. II & e. I & e. I & e. II \\
1 & 1.07 & 8.81 & 0.96 & 6.86 & \(-\)110 & \(-\)297  
The measurements of the reinforcement stationary potential were taken together with the corrosion current density and were consistent with them. In the analyzed measurement points, the increase of the corrosion current density was accompanied by a reduction of the stationary potential. On the first stage of tests, on all measurement points of A1 and A2 specimens, the stationary potential values exceeded \(-200\) mV (Figure 3) which, according to the specified criterion (Table 2) indicated a 5% probability of corrosion. The measurements of stage II in all specimens showed that the stationary potential of the reinforcement dropped, changing from E\({}_{\text{st}}<-297\) mV to E\({}_{\text{st}}>-367\) mV for A1 specimens, and from E\({}_{\text{st}}<-253\) mV to E\({}_{\text{st}}>-338\) mV for A2 specimens. Comparative analysis of results for A1 and A2 specimens (Table 3, Figure 9) showed that in A1 specimens, the reinforcement stationary potential indicated a slightly increased corrosion rate than in A2 specimens. The values obtained from the measurements of the concrete cover resistivity on all measurement points of all analyzed specimens, on both stage I and stage II of the tests, were \(\Theta<10\) k\(\Omega\)-cm (Figure 10), which would indicate \"high probability of corrosion.\" However, in this particular case, the measured values were unreliable due to the fact that the specimens were still fresh, and the hardening process had most likely not ended by the time of the test [19; 25; 29]. Figure 8: Results of the corrosion current density measurements. Figure 9: Results the measurements of the reinforcement stationary potential.