Josiane Giese

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.

The highly irregular crack pattern of reinforced concrete has been studied primarily at the surface. The ability to extend image correlation into the interior of structures by using X-ray computed tomography (CT) opens up new possibilities for analyzing the internal mechanics of concrete. In order to enable a complete material characterization, it is necessary to study the crack geometry at the micro level in 3D images over time, i.e., 4D data. This paper presents the results of in situ CT tests that were carried out on carbon-reinforced concrete (CRC) beams subjected to bending load. The main objective of the tests was the experimental analysis of the evolution of individual cracks at different stages of their formation by applying digital volume correlation (DVC) to the 4D image data from the computed tomography. The results obtained from the CT were compared with other measurement techniques, such as distributed fiber optic sensing, clip gauges, and digital image correlation (DIC).

The use of nonmetallic reinforcement in concrete aims at the decrease in material consumption by reducing the component sizes when compared to conventional reinforced concrete structures, which inherently results in very filigree structures. Although intensive basic research has been carried out on textile-reinforced concrete for about 30 years, the subject of stability behavior has hardly been investigated so far. This study focuses the fundamental understanding of the structural behavior of slender carbon-reinforced concrete (CRC) structures subjected to axial compression. Therefore, buckling experiments have been carried out in order to quantify the influence of two parameters: the slenderness ratio of the specimens (varying between 60 and 130) and the load eccentricity (0, 2, and 4 mm). The results of the specimens that were tested with the initial load eccentricities revealed a good overall agreement with those obtained by a second-order theory approach throughout all of the investigated slenderness ratios. For the centrally pressed samples that featured high slenderness ratios, the failure stresses could successfully be predicted with Euler’s buckling formula, whereas this theory overestimated the results of the specimens with intermediate to low slenderness ratios due to the plastic buckling phenomenon. The presented study emphasizes that the consideration of the stability problem is inevitable when designing material-efficient structures made of textile-reinforced concrete.