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In civil engineering, the corrosion of steel reinforcements in structural elements of concrete bares a risk of stability-reduction, mainly caused by the exposure to chlorides. 3D computed tomography (CT) reveals the inner structure of concrete and allows one to investigate the corrosion with non-destructive testing methods. To carry out such investigations, specimens with a large artificial crack and an embedded steel rebar have been manufactured. 3D CT images of those specimens were acquired in the original state. Subsequently three cycles of electrochemical pre-damaging together with CT imaging were applied. These time series have been evaluated by means of image processing algorithms to segment and quantify the corrosion products. Visualization of the results supports the understanding of how corrosion propagates into cracks and pores. Furthermore, pitting of structural elements can be seen without dismantling. In this work, several image processing and visualization techniques are presented that have turned out to be particularly effective for the visualization and segmentation of corrosion products. Their combination to a workflow for corrosion analysis is the main contribution of this work.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated. We shall show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. We will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Bi-continuous porous ceramics for filtration applications possess a particularly complicated microstructure, whereby porosity and solid matter are intermingled. Mechanical, thermal, and filtration properties can only be precisely estimated if the morphology of both solid matter and porosity can be quantitatively determined. Using 3D computed tomography (CT) at different resolutions, and several X-ray refraction-based techniques, we quantitatively evaluated porosity and pore orientation in cordierite diesel particulate filter ceramics.Moreover, applying both Fast Fourier Transform (FFT) and a newly developed image analysis algorithm (directional interface variance analysis, DIVA), we quantitatively evaluated porosity and pore orientation. Both the experimental techniques and the statistical approach allow extraction of spatially resolved or average values.Porosity values from synchrotron computed tomography used turn out to agree with mercury intrusion measurements, while pore orientation factors agree with published crystallographic texture data. This latter point also implies that the study of the pore/matter interface is sufficient to describe the morphological properties of these materials.
In order to extend the lifetime of buildings and constructions at the macro scale it is necessary to understand the damage processes of building materials at the micro scale. In particular, durability of reinforced concrete structures is one of the most important equirements for construction planning and restoration of buildings. Therefore degradation mechanisms were reproduced on laboratory specimens.
CT (Computed Tomography) is commonly used for non-destructive microstructural defect analysis for recurring tests on concrete specimens. In this work a few examples of CT applications on cementitious materials (including cement paste, mortar and concrete specimens) will be presented.
Firstly, in order to quantify the degradation processes, specimens analysed were damaged by corrosion due to carbonation and due to chloride ingress. Particular focus has been set to the analysis of cracks.
An automated crack detection tool, developed by Zuse Institut Berlin (ZIB) and BAM in ZIBAmira, has been applied for quantitative analysis of crack parameters and 3D visualization of cracks.
Furthermore the distribution of corrosion products has been evaluated inside the cement matrix and visualized in 3D data sets.
Another important factor for the ageing stability of concrete is the interfacial transition zone (ITZ). The ITZ consists of a layer of cement paste (20 to 40 μm) over every aggregate where porosity is generally increased in comparison with the bulk. This zone could be a preferential zone for transfer of aggressive species. To visualize the ITZ, a small sample of mortar with a diameter of 10mm has been prepared and scanned using the industrial μCT setup at BAM with a spatial resolution of 5μm voxel size. In addition the extracted surface of aggregates could be used for load simulations. We finally show how CT examination of drilled samples taken from building materials in conjunction with laboratory experiments is helpful for further evaluations of damage processes in concrete.
This poster presentation gives an overview of the great potential of X-ray micro computed tomography (CT) to cast light on the evolution of the microstructure in construction materials. Prevention of damage is of major economic and social importance in the development of suitable construction materials such as concrete and asphalt. Therefore a non-destructive testing method such as CT is an appropriate tool for visualization of the inner structure. Its combination with other test methods allows understanding the damage processes such as crack propagation or corrosion. We show examples of internal structure analyses on a wide range of materials: Automatic 3D crack detection and the visualization of corrosion products inside of steel reinforced concrete, pore and shape analysis of lightweight aggregates and the visualization of deformation of high-pressure loaded aerated concrete specimens, distribution of aggregates inside concrete, and determination of the surface of porous asphalt core samples. Segmented structures serve, e.g., as input data for simulation of transport phenomena or virtual load tests.
Evaluating porosity in cordierite diesel particulate filter materials, part 1 X-ray refraction
(2013)
Bi-continuous porous ceramics for filtration applications possess a particularly complicated microstructure, with porosity and solid matter being intermingled. Mechanical, thermal, and filtration properties can only be precisely estimated if the morphology of both solid matter and porosity can be quantitatively determined. Using x-ray absorption and refraction, we quantitatively evaluate porosity and pore orientation in cordierite diesel particulate filter ceramics. Porosity values turn out to agree with mercury intrusion measurements, while pore orientation factors agree with published crystallographic texture data.
Complementary to Part 1 of this work, the bi-continuous microstructure of porous synthetic cordierite ceramics for filtration applications was investigated using 3D x-ray computed tomography at different resolutions. Applying both Fast Fourier Transform and a newly developed image analysis algorithm, we quantitatively evaluated porosity and pore orientation. The statistical approach allows extraction of spatially resolved or average values. Porosity values based on x-ray absorption agree with mercury intrusion measurements, while pore orientation factors agree with x-ray refraction data (Part 1 of this work), and with published crystallographic texture data.
Micro gears are applied in an increasing quantity in many applications. Therefore, precise measurements are of growing importance to ensure their quality. This contribution describes the measurement of gears of a micro planetary gear set with a tactile probe, a tactile-optical probe, an optical sensor, and computed tomography (CT). For the tactile measurements, a high precision piezoresistive microprobe was used. A so-called fiber probe was applied for tactile-optical measurements. This probe applies image processing to determine the position of the tactile probing element. For all tactile and tactile-optical measurements, single point probing was used. The optical measurements were carried out with an imaging sensor based on focus variation. Due to limited accessibility, on some gears not all regions could be measured by the optical sensor and the tactile-optical probe. In contrast to this, with CT the whole part could be measured with high point density. We used a micro-CT system and carried out measurements with Synchrotron-CT. All the sensors used deliver measurement data in Cartesian coordinates. It is a challenge to transfer these data into coordinates in which gear parameters are defined. For this, special attention must be paid to the determination of the gear axis and to the orientation of the teeth. The applied procedures are detailed for different micro gears. The comparison between data of different measurements was carried out successfully. The deviations between the CT data and the tactile or tactile-optical data lie in the range of only a few micrometers.