Citation: Liebold, F.; Wagner, F.; Giese, J.; Grzesiak, S.; de Sousa, C.; Beckmann, B.; Pahn, M.; Marx, S.; Curbach, M.; Maas, H.-G. Damage Analysis and Quality Control of Carbon-Reinforced Concrete Beams Based on In Situ Computed Tomography Tests. Buildings 2023, 13, 2669. https://doi.org/10.3390/ buildings13102669 Academic Editor: Rajai Zuheir Al-Rousan Received: 4 September 2023 Revised: 26 September 2023 Accepted: 12 October 2023 Published: 23 October 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). buildings Article Damage Analysis and Quality Control of Carbon-Reinforced Concrete Beams Based on In Situ Computed Tomography Tests Frank Liebold 1, * ,† , Franz Wagner 1,† , Josiane Giese 2,† , Szymon Grzesiak 3,† , Christoph de Sousa 3,† , Birgit Beckmann 2 , Matthias Pahn 3 , Steffen Marx 2 , Manfred Curbach 2 and Hans-Gerd Maas 1 1 Institute of Photogrammetry and Remote Sensing, TUD Dresden University of Technology, 01062 Dresden, Germany; franz.wagner@tu-dresden.de (F.W.); hans-gerd.maas@tu-dresden.de (H.-G.M.) 2 Institute of Concrete Structures, TUD Dresden University of Technology, 01062 Dresden, Germany; josiane.giese@tu-dresden.de (J.G.); birgit.beckmann@tu-dresden.de (B.B.); steffen.marx1@tu-dresden.de (S.M.); manfred.curbach@tu-dresden.de (M.C.) 3 Department of Civil Engineering, RPTU Kaiserslautern-Landau, 67663 Kaiserslautern, Germany; szymon.grzesiak@rptu.de (S.G.); christoph.desousa@rptu.de (C.d.S.); matthias.pahn@rptu.de (M.P.) * Correspondence: frank.liebold@tu-dresden.de † These authors contributed equally to this work. Abstract: Carbon-reinforced concrete (CRC) is increasingly utilized in construction, due to its unique properties, such as corrosion resistance, high-tensile strength, and durability. Understanding its behavior under different loads is crucial to ensuring its safe and effective use in various construction applications. In this study, three-point bending tests were performed in combination with large-scale in situ computed tomography (CT). This paper presents the related three- and four-dimensional evaluation methods, with emphasis on crack width and quality control. The focus was on large CRC beams, with cross-sectional sizes of up to 80 mm by 160 mm. Such dimensions require extremely high energy during a CT scan. Therefore, a new experimental setup with energies of up to 8 MeV was used in this study. However, such high energies posed new challenges to the analysis methods. Therefore, two methods (digital volume correlation and grayscale profile analysis) for accurate crack width estimation were adapted and applied to the 3D reconstructions. In addition, a photogrammetric stereo image sequence was acquired and analyzed, using digital image correlation to cross-validate the results derived from the 3D crack width estimates. The 3D CT images also played a key role in the quality control measures, including the localization of the carbon-reinforcement and the assessment of porosity within the concrete structure. Keywords: crack analysis; X-ray tomography; photogrammetry; digital image correlation (DIC); digital volume correlation (DVC); 3D segmentation 1. Introduction Concrete is currently the most important material for both residential and infrastruc- ture construction. This versatile material has undergone a transformative evolution with the introduction of carbon-reinforced concrete (CRC), which is a composite material of fine-grained concrete and carbon reinforcement. As a result, it is resistant to corrosion—a key feature that has far-reaching implications for structural design. The corrosion resistance provides a profound advantage, by allowing the concrete cover to be reduced to a minimum, since it results only from the bond requirements. In contrast to steel-reinforced concrete, the condition for compliance with durability can be omitted [1]. This feature alone transforms the possibilities of construction, allowing the creation of delicate, thin-walled members and structures, whether flat or curved. This innovation not only enhances the aesthetic potential of construction, but also takes a giant leap towards material conservation, which is instrumental in sustainable design strategies. Buildings 2023, 13, 2669. https://doi.org/10.3390/buildings13102669 https://www.mdpi.com/journal/buildings