## 5 Conclusions  
This paper focused on AE source localization of damage due to corrosion in RC. Three sample scales were investigated: a small mortar sample (scale 1), RC prisms (scale 2), and RC beams (scale 3). For each scale, the corrosion process was accelerated by an imposed direct current. It is found that the AE technique can detect corrosion in RC. However, it is observed that dedicated filtering is necessary to reliably localize AE events. For this purpose, a new post-processing protocol was developed by combining existing methods to improve the arrival time picking and filters. A better estimation of the wave's arrival time is obtained by applying the Akaike Information Criterion (AIC). Afterwards, signals are filtered based on their signal to-noise ratio (S/N) and accuracy of the arrival time picking. The novelty of the work lies in the validation of the developed protocol by means of extensive experimental results obtained during accelerated corrosion experiments. It is proven that the developed post-processing protocol significantly improves the localization result on all three sample scales. On the smallest sample scales, scales 1 and 2, a 3D sensor layout was applied. It was found that 3D localization can localize initial internal cracking which could be verified with X-ray images (scale 1), crack measurements (scale 2), and determination of the mass loss (scale 2). As damage progresses, crack growth is more difficult to localize correctly. Localization in 3D may be valuable in a laboratory environment, e.g., to validate cluster  
Figure 17: Top view of the unfiltered localized AE events of Beam-2 with indication the cracks that were visible on the surface. Figure 18: Top view of the localization results of Beam-2 with indication of the error ellipses and cracks that were visible on the surface. algorithms to differentiate AE sources. When larger areas need to be monitored, a 2D sensor layout may be more convenient. Therefore, for the RC beams (scale 3), a 2D sensor layout was used as the assessment of a larger monitoring area was desired. Localization results were verified by comparison with crack measurements. Corrosion and initial micro-cracking were localized correctly. A larger error is noticed during crack growth as this is a 3D phenomenon. For all scales, it was found that post-processed AE results enabled the detection and localization of corrosion-induced damage correctly and earlier than a visual inspection. The developed protocol can serve as a valuable and reliable alternative to computationally demanding localization algorithms. The applied method allows the prediction of where the visual damage will be first observed. This advantage can be useful during on-site monitoring to provide well-informed decisions on maintenance and repair. This paper presented both 2D and 3D localization setups which both have advantages and disadvantages. In actual structures, the extent of the measuring zone should be considered against the desired accuracy of the localization result. As a first assessment of the structure, sensors may be spread over a larger area and less sensors will be available for localization. A 2D sensor layout may be suitable to cover this larger area and have sufficient information to pinpoint the most damaged zones. Afterwards, the areas of interest can be monitored with a 3D sensor setup for a more detailed assessment. On-site application will be part of future research. Conceptualization, C.V.S. and E.V. ; methodology, C.V.S. and E.V. ; software, C.V.S. ; validation, C.V.S. ; translation analysis, C.V.S. ; investigation, C.V.S. ; resources, E.V. ; data curation, C.V.S. ; writing--original draft preparation, C.V.S. ; writing--review and editing, C.V.S. and E.V. ; visualization, C.V.S. ; supervision, E.V. ; project administration, E.V. ; funding acquisition, C.V.S. and E.V. All authors have read and agreed to the published version of the manuscript.