Portland cement pastes analysed by synchrotron and laboratory X-ray imaging

Portland Cement (PC) is the most used construction material and the derived building materials have very complex hierarchical microstructures. Quantitative characterization of their microstructures is of paramount importance for assessing the performance and durability of the final products. As cement performance is controlled by its phase composition and microstructure, in particular, the pore network plays a critical role in the mechanical properties and durability. The chemical and hydration changes in PC binders affect their performances mainly because of the binding properties of the main component, the so-called C-S-H gel. Here, we analyse porosity in PC pastes using laboratory and synchrotron X-ray micro-tomography with different water to cement mass ratios (w/c) after 28 days of hydration. Monochromatic synchrotron X-ray microtomography is used for reference and the main aim is determining volume percentage of different components with focus on porosity. It will be shown, as expected, that higher amount of water (that increases fluidity of pastes) results in higher porosities at 28 days of hydration. Therefore, in the histogram and tomograms more pores, hydrated materials, and less anhydrous materials would appear with increasing w/c (see Figure 1). The excellent spatial resolution (and slightly better contrast) of synchrotron experiments serve as reference for data analysis. Despite 0.2-0.3 m voxel-sizes in all the used experimental setups (see Figure 2), the laboratory tomograms show some limitations that will be discussed. In this work, a two-steps approach is followed. Firstly, we will report the analysis of the histograms by classifying in the three types of components based on grey-levels: i) pores, ii) hydrated components; and iii) unreacted cement phases. Secondly, segmented pore contribution will be further analyzed and the results from laboratory tomograms will be compared with the reference values derived from synchrotron data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Ghost Tomography

Ghost tomography using single-pixel detection extends the emerging field of ghost imaging to three dimensions, with the use of penetrating radiation. In this work, a series of spatially random x-ray intensity patterns is used to illuminate a specimen in various tomographic angular orientations with only the total transmitted intensity being recorded by a single-pixel camera (or bucket detector). The set of zero-dimensional intensity readings, combined with knowledge of the corresponding two-dimensional illuminating patterns and specimen orientations, is sufficient for three-dimensional reconstruction of the specimen. The experimental demonstration of ghost tomography is presented here using synchrotron hard x-rays. This result expands the scope of ghost imaging to encompass volumetric imaging (i.e., tomography), of optically opaque objects using penetrating radiation. For hard x-rays, ghost tomography has the potential to decouple image quality from dose rate as well as image resolution from detector performance

Auditory chain reaction: Effects of sound pressure and particle motion on auditory structures in fishes

Despite the diversity in fish auditory structures, it remains elusive how otolith morphology and swim bladder-inner ear (= otophysic) connections affect otolith motion and inner ear stimulation. A recent study visualized sound-induced otolith motion;but tank acoustics revealed a complex mixture of sound pressure and particle motion. To separate sound pressure and sound-induced particle motion, we constructed a transparent standing wave tubelike tank equipped with an inertial shaker at each end while using X-ray phase contrast imaging. Driving the shakers in phase resulted in maximised sound pressure at the tank centre, whereas particle motion was maximised when shakers were driven out of phase (180 degrees). We studied the effects of two types of otophysic connections-i.e. the Weberian apparatus (Carassius auratus) and anterior swim bladder extensions contacting the inner ears (Etroplus canarensis)-on otolith motion when fish were subjected to a 200 Hz stimulus. Saccular otolith motion was more pronounced when the swim bladder walls oscillated under the maximised sound pressure condition. The otolith motion patterns mainly matched the orientation patterns of ciliary bundles on the sensory epithelia. Our setup enabled the characterization of the interplay between the auditory structures and provided first experimental evidence of how different types of otophysic connections affect otolith motion

Boosting spatial resolution by incorporating periodic boundary conditions into single-distance hard-x-ray phase retrieval

A simple coherent-imaging method due to Paganin et al. is widely employed for phase-amplitude reconstruction of samples using a single paraxial x-ray propagation-based phase-contrast image. The method assumes that the sample-to-detector distance is sufficiently small for the associated Fresnel number to be large compared to unity. The algorithm is particularly effective when employed in a tomographic setting, using a single propagation-based phase-contrast image for each projection. Here we develop a simple extension of the method, which improves the reconstructed contrast of very fine sample features. This provides first-principles motivation for boosting fine spatial detail associated with high Fourier frequencies, relative to the original method, and was inspired by several recent works employing empirically-obtained Fourier filters to a similar end

Zu den Wurzeln der Modernen Architektur, Teil I

Modern emerging technologies, such as additive manufacturing, bioprinting, and new material production, require novel metrology tools to probe fundamental high-speed dynamics happening in such systems. Here we demonstrate the application of the megahertz (MHz) European X-ray Free-Electron Laser (EuXFEL) to image the fast stochastic processes induced by a laser on water-filled capillaries with micrometer-scale spatial resolution. The EuXFEL provides superior contrast and spatial resolution compared to equivalent state-of-the-art synchrotron experiments. This work opens up new possibilities for the characterization of MHz stochastic processes on the nanosecond to microsecond time scales with object velocities up to a few kilometers per second using XFEL sources