Improved mesoscale segmentation of concrete from 3D X-ray images using contrast enhancers

Carrara, Pietro; Kruse, Rolf; Bentz, Dale P.; Lunardelli, Matteo; Leusmann, Thorsten; Varady, Patrick A.; Lorenzis, Laura De

doi:10.1016/j.cemconcomp.2018.06.014

Cited by 54 publications

(17 citation statements)

References 29 publications

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“…Prior to usage in the cement paste, the fibers were oxidatively heat treated in an open furnace at 425°C for 2 h to remove the sizing and to oxidize the carbon fiber's surface, improving wettability and fiber-matrix bonding [15,36,37]. Barium sulfate is added to increase the X-ray absorption of the cementitious matrix and thus to increase the electron density contrast with respect to other embedded materials, especially the carbon fibers [38]. All components used for sample preparation are given in Table 1 This process leads to an almost unidirectional fiber alignment along the movement path of the nozzle; the fiber orientation within representative volume elements of the test specimens are quantified by X-ray CT measurements.…”

Section: Sample Preparation Of Miniature Beamsmentioning

confidence: 99%

Influence of fiber alignment on pseudoductility and microcracking in a cementitious carbon fiber composite material

et al. 2021

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This research examines the effect of fiber alignment on the performance of an exceptionally tough 3D-printable short carbon fiber reinforced cementitious composite material, the flexural strength of which can exceed 100 N/mm2. The material shows pseudoductility caused by strain-hardening and microcracking. An extrusion-based manufacturing process allows accurate control over the spatial alignment of the fibers’ orientation, since extrusion through a tight nozzle leads to nearly unidirectional alignment of the fibers with respect to the directional movement of the nozzle. Specimens were investigated using mechanical tests (flexural and tensile load), augmented by non-destructive methods such as X-ray 3D computed tomography and acoustic emission analysis to gain insight into the microstructure. Additionally, digital image correlation is used to visualize the microcracking process. X-ray CT confirms that about 70% of fibers show less than 10° deviation from the extrusion direction. Systematic variations of the fiber alignment with respect to the direction of tensile load show that carbon fibers enhance the flexural strength of the test specimens as long as their alignment angle does not deviate by more than 20° from the direction of the acting tensile stress. Acoustic emission analysis is capable of evaluating the spatiotemporal degradation behavior during loading and shows consistent results with the microstructural damage observed in CT scans. The strong connection of fiber alignment and flexural strength ties into a change from ductile to brittle failure caused by degradation on a microstructural level, as seen by complementary results acquired from the aforementioned methods of investigation.

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Section: Sample Preparation Of Miniature Beamsmentioning

confidence: 99%

Influence of fiber alignment on pseudoductility and microcracking in a cementitious carbon fiber composite material

et al. 2021

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“…1. Barium sulfate was added to improve the contrast between the cementitious matrix and fibers or other inclusions [31].…”

Section: Optimization Of Printability and Mixture Designmentioning

confidence: 99%

3D printing as an automated manufacturing method for a carbon fiber-reinforced cementitious composite with outstanding flexural strength (105 N/mm2)

et al. 2021

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As research interest in the additive manufacturing of cementitious materials for structural uses has been continuously increasing, the question of how to incorporate tensile reinforcement in an automated process has gained further importance. Our research describes a carbon fiber-reinforced cementitious composite produced by common extrusion techniques applied in 3D printing as a means to effectively control fiber alignment. Optimization of the mixture design and consistency allows for admixing up to 3 vol.-% chopped carbon fibers, leading to specimens that can reach a flexural strength exceeding 100 N/mm2 without the addition of further continuous reinforcement. Fiber integrity during the process was checked using optical microscopy. Analysis of the microstructure shows that approximately 70% of the fibers are aligned within ± 5° of a preferential direction. Micromechanical single-fiber push-out tests confirm an interfacial fracture toughness typical for strain-hardening systems. The first insights into a ‘lost formwork’ approach commonly employed in 3D printing show that the reinforcement remains effective even when combined with nonreinforced mortar.

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“…To investigate the interface between two layers on a microscopic scale, drilling cores (diameter 30 mm) are taken from the specimen. Since baryte powder is placed in between layers 3 and 4 during production of the layers, the interface with baryte powder can be examined in more detail [55]. The specimen is placed into a µCT and 3D scanned (GE phoenix, Boston, MA, USA, voltage: 160 kV, current: 230 µA, number of images: 1000, image average: 3, filter: 0.1 mm Cu, exposure: 500 ms for all specimen, voxel edge length: 33.7 µm).…”

Section: Investigations On Interlayer Characteristicsmentioning

confidence: 99%

The Effect of Accelerator Dosage on Fresh Concrete Properties and on Interlayer Strength in Shotcrete 3D Printing

2020

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Recently, the progress in 3D concrete printing has developed enormously. However, for the techniques available, there is still a severe lack of knowledge of the functional interaction of processing technology, concrete rheology and admixture usage. For shotcrete 3D printing technology, we present the effect of accelerator dosages (0%, 2%, 4% and 6%) on fresh concrete properties and on interlayer strength. Therefore, early yield stress development up to 90 min is measured with penetration resistance measurements. Deformation of layers under loading is investigated with digital image correlation and a mechanical testing machine. One point in time (10 min after deposition) is examined to quantify vertical buildability of elements depending on the accelerator dosage. Four different interlayer times (0, 2, 5 and 30 min), which occur for the production of small and large elements as well as due to delay during production, are investigated mechanically as well as quantitatively with computed tomography regarding the formation of cold joints. With increased accelerator dosage, an instantaneous increase in early age yield stress and yield stress evolution was observed. An increase in interlayer time leads to a reduced strength. This is mainly attributed to the observed reduced mechanical interlocking effect of the strands. Finally, a model to describe interlayer quality is presented. In the end, advantages as well as limitations of the findings are discussed.

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Improved mesoscale segmentation of concrete from 3D X-ray images using contrast enhancers

Cited by 54 publications

References 29 publications

Influence of fiber alignment on pseudoductility and microcracking in a cementitious carbon fiber composite material

Influence of fiber alignment on pseudoductility and microcracking in a cementitious carbon fiber composite material

3D printing as an automated manufacturing method for a carbon fiber-reinforced cementitious composite with outstanding flexural strength (105 N/mm2)

The Effect of Accelerator Dosage on Fresh Concrete Properties and on Interlayer Strength in Shotcrete 3D Printing

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