Open Access

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.

Larger high pressure die castings (HPDC) and decreasing wall thicknesses are raising the issue of casting defects like pores in aluminum structures. Properties of components are often strongly influenced by inner porosity. As these products are being established more and more in lightweight construction (e.g. automotive and other transport areas), non-destructive testing methods, which can be applied fast and on-site, are required for quality assurance. In this contribution, the application of active thermography for the direct detection of larger pores is demonstrated. The analysis of limits and accuracy of the method are completed by numerical simulation and the method is validated using computed tomography.

Integration of fiber reinforcement in high-performance cementitious materials has become widely applied in many fields of construction. One of the most investigated advantages of steel Fiber reinforced concrete (SFRC) is the deceleration of crack growth and hence its improved sustainability. Additional benefits are associated with its structural properties, as fibers can significantly increase the ductility and the tensile strength of concrete. In some applications it is even possible to entirely replace the conventional reinforcement, leading to significant logistical and environmental benefits. Fiber reinforcement can, however, have critical disadvantages and even hinder the Performance of concrete, since it can induce an anisotropic material behavior of the mixture if the fibers are not appropriately oriented. For a safe use of SFRC in the future, reliable non-destructive testing (NDT) methods need to be identified to assess the fibers’ orientation in hardened concrete. In this study, ultrasonic material testing, electrical impedance testing, and X-ray computed tomography have been investigated for this purpose using specially produced samples with biased or random Fiber orientations. We demonstrate the capabilities of each of these NDT techniques for fiber orientation measurements and draw conclusions based on these results about the most promising areas for future research and development.

The osseointegration in/around additively manufactured (AM) lattice structures of a new titanium alloy, Ti–19Nb–14Zr, was evaluated. Different lattices with increasingly high sidewalls gradually closing them were manufactured and implanted in sheep. After removal, the bone–interface implant (BII) and bone–implant contact (BIC) were studied from 3D X-ray computed tomography images. Measured BII of less than 10 µm and BIC of 95% are evidence of excellent osseointegration. Since AMnaturally leads to a high-roughness surface finish, the wettability of the implant is increased. The new alloy possesses an increased affinity to the bone. The lattice provides crevices in which the biological tissue can jump in and cling. The combination of these factors is pushing ossification beyond its natural limits. Therefore, the quality and speed of the ossification and osseointegration in/around these Ti–19Nb–14Zr laterally closed lattice implants open the possibility of bone spline key of prostheses. This enables the stabilization of the implant into the bone while keeping the possibility of punctual hooks allowing the implant to be removed more easily if required. Thus, this new titanium alloy and such laterally closed lattice structures are appropriate candidates to be implemented in a new generation of implants.