Abstract
Grating-based X-ray dark-field tomography is a promising technique for biomedical and materials research. Even if the resolution of conventional X-ray tomography does not suffice to resolve relevant structures, the dark-field signal provides valuable information about the sub-pixel microstructural properties of the sample. Here, we report on the potential of X-ray dark-field imaging to be used for time-resolved three-dimensional studies. By repeating consecutive tomography scans on a fresh cement sample, we were able to study the hardening dynamics of the cement paste in three dimensions over time. The hardening of the cement was accompanied by a strong decrease in the dark-field signal pointing to microstructural changes within the cement paste. Furthermore our results hint at the transport of water from certain limestone grains, which were embedded in the sample, to the cement paste during the process of hardening. This is indicated by an increasing scattering signal which was observed for two of the six tested limestone grains. Electron microscopy images revealed a distinct porous structure only for those two grains which supports the following interpretation of our results. When the water filled pores of the limestone grains empty during the experiment the scattering signal of the grains increases.
Highlights
Recent advances show promise to even increase the value of X-ray imaging for such applications
By acquiring several consecutive dark-field CTs of a fresh cement sample containing some limestone grains, we show that the hydration dynamics within the cement paste can even be studied in three dimensions over the course of 37 hours
We observed an increase of the scattering signal when aggregates such as limestone grains were added to the cement paste in further experiments
Summary
Recent advances show promise to even increase the value of X-ray imaging for such applications. The essential mechanism which hardens the cement paste is the hydration of these compounds leading to an interconnected network of hydration products When studying this reaction a very distinct drop of the scattering signal was observed in dark-field images acquired throughout the process of hardening[22]. This finding offers the possibility to study local deviations from the hydration dynamics of the cement paste, something that is impossible with conventional testing techniques which only provide bulk information on the hydration dynamics in large samples[23]. Our results are further supported by polarized light microscopy (PLM) and scanning electron microscopy (SEM) experiments revealing a distinct pore system for the affected grains
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