## 3 Experimental Test Program and Results
### Corrosion Damage Localization in RC Prisms  
The second sample scale contains two RC prisms with dimensions 150 \(\times\) 150 \(\times\) 250 mm\({}^{3}\) that were monitored with a 3D AE sensor setup. The first sample was reinforced with one ribbed rebar with a nominal diameter of 14 mm in the center and will be referred to as AE-1. A length of 42 mm was bonded to the concrete and was able to corrode. The second sample was identical, but also had a stirrup with a diameter of 6 mm. The stirrup was placed around the main rebar and was connected to the mold with cable ties, following the setup  
Figure 4: Unfiltered localized AE events; (**left**) view parallel to rebar, (**right**) view perpendicular to rebar. Figure 5: Localization results after applying the post-processing protocol with indication of the error ellipsoids, cracks, and corrosion products; (**left**) view parallel to rebar, (**middle**) view perpendicular to rebar, and (**right**) 3D view. Figure 3: Schematic representation of the accelerated corrosion setup and 3D sensor configuration with six AE sensors (S1–S6) of scale 1.  
presented by [PERSON] et al. [8]. The stirrup could corrode as it was connected with a copper wire to the main rebar. The second sample will be referred to as AE-2. The accelerated corrosion setup was scaled up from the mortar samples and is shown in Figure 6. A visual inspection was carried out every week during which crack width measurements were performed with a crack meter. The accuracy of the crack meter was 0.05 mm. The sample size was too large to allow for 3D-XCT analysis. The same AMSY-6 Vallen acquisition system with six channels was used. For this sample scale, broadband piezoelectric sensors with a flat frequency response between 100 and 400 kHz were attached on the specimen surface with hot melt glue. The sensor arrangement is shown in Figure 6. The amplitude threshold, the pre-trigger time, duration discrimination time, and rearm time were set to 40 dB, 20 \(\upmu\)s, 400 \(\upmu\)s, and 0.4 ms, respectively. The sampling rate was set to 10 MHz. With 2048 samples being stored, the length of the stored signal was 204.8 \(\upmu\)s. The digital frequency filter was set between 95 and 850 kHz. Figure 7 shows the AE source localization results without applying the post-processing protocol. The corroding part of the rebar is colored in dark grey. The bottom side of the rebar where most mass loss was observed after cleaning the rebar, is indicated in red. A mass loss of 4.03% was reached. Many reflections can be observed in the top part of the sample. The cracks on the bottom side and at the side of sensors 5 and 6 are not correctly localized. Please note that all AE sensors were positioned at the top half of the sample, as the bottom part was immersed in salt solution. After applying the post-processing protocol, the AE localization result improved significantly as shown in Figure 8. The events that were localized by 4 sensors are again indicated with a different marker than the events localized by 5 or 6 sensors. For the latter, the error ellipsoids are also shown. The radius of the error ellipsoid was chosen to be maximum 10 mm in every direction. Figure 6: Schematic representation of the accelerated corrosion setup and 3D AE sensor configuration with six AE sensors (S1–S6) of scale 2. A crack, perpendicular to the rebar, could be noticed at the bottom side of the sample at the end of the experimental program. This crack is further denoted as crack 1. A second smaller crack at the side of sensors 5 and 6 and parallel to the rebar was observed. This crack will be further denoted as crack 2. It can be seen that most AE events are localized around the rebar, reaching the side of the sample where crack 2 was observed. Less AE events are localized near crack 1 due to the AE sensors being positioned on the top half of the sample. Before the accelerated corrosion test, pencil lead breaks (PLB) were performed on the samples.