## 3 Accelerated Corrosion Testing of the Reactor Concrete Block  
### Experimental Program  
A reinforced concrete block was cut from the reactor facility with a length, width, and depth of 7 feet 4 inches, 3 feet, and 3 feet 4 inches, respectively. An accelerated corrosion test was conducted to corrode three different areas over the course of this study. Three concrete cores were drilled (3 inches in diameter and 9 inches in length) at three locations to create different concrete cover thickness for three vertical steel reinforcing bars adjacent to the cores (Figure 15). During the coring process, a transverse reinforcing bar was unavoidably cut at a depth of approximately 6 inches from the surface of the concrete test block specimen.  
The test was initiated by placing 3% NaCl solution in the drilled holes to a depth of 3 inches on 2 December 2014. The solution was maintained in the drilled holes for two months to ensure that chloride concentration reached a needed level for corrosion initiation [29; 30]. Wet/dry cycles were then initiated (three days wet and four days dry) on 19 February 2015 to accelerate the corrosion process. A galvanic cell was created during the wet days by inserting a copper plate in the cored locations. Figure 15d shows the 'as measured' concrete cover after the cores were drilled.  
The first location has a concrete cover of 0.25 inches and was monitored using three broadband sensors (WDI) and one resonant sensor (R15I) while the second location has a cover of 1.0 inch and was monitored using four resonant sensors (R6I). The third location has a cover of 0.125 inches and was monitored using eight resonant sensors (R6I). On 22 May 2015 one of the sensors at the 1.0 inch cover location was removed from the test block and, on 27 May 2015, it was placed on a small concrete specimen (control specimen) with dimensions of 3.0 inches \(\times\) 3.0 inches \(\times\) 11.25 inches. The control specimen is not reinforced and, therefore, is known not to have corrosion activity. Data collected from the control specimen was used to verify the efficiency of the data filters developed during the course of the project. Acoustic emission activity was recorded continuously throughout the test period.  
Half-cell potential (HCP) and linear polarization resistance (LPR) measurements were recorded once a week with the objective of providing insight related to the corrosion process of targeted reinforcement locations. HCP method is described in ASTM C876 [31] and is traditionally employed to determine the likelihood of corrosion activity, which is described in Table 3. Linear polarization resistance (LPR) is a method used to measure polarization resistance (_Rp_), which can be used to  
Figure 14: Source location results at the +48 level. Red dots indicate located AE events.  
calculate corrosion current (_Icorr_) and corrosion current density (_icorr_). These parameters can be used to estimate the corrosion rate (_CR_). Figure 16 shows a schematic of the test setup and acoustic emission sensor layout to monitor the corrosion process of the reinforcing bars. A schematic of the aged concrete block control specimen is also shown in this figure.  
Figure 16: Schematic of aged reactor concrete test block: (**a**) Left side view, (**b**) front view, (**c**) right side view, (**d**) top view, and (**e**) control location.  
Figure 15: Aged concrete block specimen: (**a**) Left side view, (**b**) front view, (**c**) right side view, (**d**) top view, and (**e**) control location.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Potential Against Cu-CuSO4 Electrode** & **Corrosion Condition** \\ \hline \(>\)\(-\)200 mV & Low risk (10\% probability of corrosion) \\ \(-\)200 to \(-\)350 mV & Intermediate corrosion risk \\ \(<\)\(-\)350 mV & High corrosion risk (90\% probability) \\ \(<\)\(-\)500 mV & Severe corrosion damage \\ \hline \hline \end{tabular}
\end{table}
Table 3: ASTM corrosion for Cu-CuSO4 reference electrode [31].