Advancing the visualization of pure water transport in porous materials by fast, talbot interferometry-based multi-contrast x-ray micro-tomography

Abstract

The spatio-temporal distribution (4D) of water in porous materials plays a fundamental role in many natural and technological processes. The dynamics of water transport is strongly entangled with the material's pore-scale structure. Understanding their correlation requires imaging simultaneously the 4D water distribution and the porous microstructure. To date, 4D images with high temporal and spatial resolution have been mainly acquired by attenuation-based X-ray micro-tomography, whereby pure water is substituted by saline solutions with high atomic number components to improve image contrast. The use of saline solutions is however not always desirable, as the altered fluid properties may affect the transport process as well or, as it is the case for hydrating cement-based materials, they may modify the chemical reactions and their kinetics. In this study, we aimed at visualizing pure water transport in porous building materials by a new implementation of fast Talbot interferometry-based multi-contrast X-ray micro-tomography at the P07 beamline of the Helmholtz-Zentrum Geesthacht at DESY. We report results from a mortar specimen imaged at three different stages during evaporative drying. We show the possibility of visualizing simultaneously the microstructure and the pore-scale water redistribution by the phase contrast images. In addition, different solid material phases are clearly distinguished in these images. The higher contrast between water and the porous substrate, achievable in the phase contrast images, compared with the attenuation ones, empowers new analysis and allows investigating the correlation between the drying process and the porous microstructure. The approach offers the possibility of studying other chemically inert or reactive water transport processes without any chemical or physical perturbation of the processes themselves.

X-ray dark-field contrast imaging of water transport during hydration and drying of early-age cement-based materials

“…(1)). In previous work, we have demonstrated, for porous building materials, the higher sensitivity of XPCI to pure water content changes in pores with size above the spatial resolution of the tomograms, compared with corresponding results obtained, on the same specimens and with the same X-ray source and detector, by XACI [48,49]. The reason for the higher contrast by XPCI is twofold: 1) the difference in values between pure water and air, normalized by the value of the solid substrate, is larger than the respective normalized difference for the values (see achieves larger values than , for both water and any material phase of the solid substrate, e.g., cement hydration products (see Figure 4(c) in [49]), and at any X-ray photon energy.…”

Tunable X-ray dark-field imaging for sub-resolution feature size quantification in porous media

“…It has already been shown that DFI can detect sub-resolution features qualitatively 19,26,40,28,[33][34][35][36][37][38][39] , but until now, methods demonstrating quantification of the size of the unresolved porosity have not been presented in published research. In this research, we present a method to estimate the size of the unresolved pores in a material, based tunable grating interferometry performed at the TOMCAT beamline of the Swiss Light Source (Paul Scherrer Institut).…”

X-ray Phase-Contrast Imaging Using Near-Field Speckles

“…X-ray absorption-based microCT has successfully been explored for the characterisation of mortar samples for over two decades [Bentz et al, 1994;Chotard et al, 2003;Carrara et al, 2018]. More recently, it has been recognised in the materials science community that X-ray phase-contrast imaging can often deliver images with superior contrast than conventional absorption CT and multi-modal imaging, exploiting the absorption-, phase-contrast and dark-field signals, can provide complementary information as demonstrated with X-ray grating interferometry [Sarapata et al, 2015;Yang et al, 2016bPrade et al, 2016].…”