Blykers Benjamin K, Organista Caori, Kagias Matias, Marone Federica, Stampanoni Marco, Boone Matthieu N, Cnudde Veerle, Aelterman Jan
Pore-Scale Processes in Geomaterials Research Group (PProGRess), Department of Geology, Ghent University, 9000 Ghent, Belgium.
Ghent University Centre for X-ray Tomography (UGCT), 9000 Ghent, Belgium.
J Imaging. 2022 Oct 14;8(10):282. doi: 10.3390/jimaging8100282.
Mineral building materials suffer from weathering processes such as salt efflorescence, freeze-thaw cycling, and microbial colonization. All of these processes are linked to water (liquid and vapor) in the pore space. The degree of damage following these processes is heavily influenced by pore space properties such as porosity, pore size distribution, and pore connectivity. X-ray computed micro-tomography (µCT) has proven to be a valuable tool to non-destructively investigate the pore space of stone samples in 3D. However, a trade-off between the resolution and field-of-view often impedes reliable conclusions on the material's properties. X-ray dark-field imaging (DFI) is based on the scattering of X-rays by sub-voxel-sized features, and as such, provides information on the sample complementary to that obtained using conventional µCT. In this manuscript, we apply X-ray dark-field tomography for the first time on four mineral building materials (quartzite, fired clay brick, fired clay roof tile, and carbonated mineral building material), and investigate which information the dark-field signal entails on the sub-resolution space of the sample. Dark-field tomography at multiple length scale sensitivities was performed at the TOMCAT beamline of the Swiss Light Source (Villigen, Switzerland) using a Talbot grating interferometer. The complementary information of the dark-field modality is most clear in the fired clay brick and roof tile; quartz grains that are almost indistinguishable in the conventional µCT scan are clearly visible in the dark-field owing to their low dark-field signal (homogenous sub-voxel structure), whereas the microporous bulk mass has a high dark-field signal. Large (resolved) pores on the other hand, which are clearly visible in the absorption dataset, are almost invisible in the dark-field modality because they are overprinted with dark-field signal originating from the bulk mass. The experiments also showed how the dark-field signal from a feature depends on the length scale sensitivity, which is set by moving the sample with respect to the grating interferometer.
矿物建筑材料会遭受诸如盐析、冻融循环和微生物定殖等风化过程。所有这些过程都与孔隙空间中的水（液态和气态）有关。这些过程后的损伤程度受孔隙率、孔径分布和孔隙连通性等孔隙空间特性的严重影响。X射线计算机显微断层扫描（µCT）已被证明是一种用于无损三维研究石材样品孔隙空间的有价值工具。然而，分辨率和视野之间的权衡常常阻碍对材料特性得出可靠结论。X射线暗场成像（DFI）基于亚体素尺寸特征对X射线的散射，因此提供了与使用传统µCT获得的信息互补的样品信息。在本手稿中，我们首次将X射线暗场断层扫描应用于四种矿物建筑材料（石英岩、烧制粘土砖、烧制粘土屋顶瓦和碳酸盐矿物建筑材料），并研究暗场信号在样品亚分辨率空间中包含哪些信息。使用Talbot光栅干涉仪在瑞士光源（瑞士维利根）的TOMCAT光束线进行了多长度尺度灵敏度的暗场断层扫描。暗场模态的互补信息在烧制粘土砖和屋顶瓦中最为明显；在传统µCT扫描中几乎无法区分的石英颗粒，由于其低暗场信号（均匀亚体素结构）在暗场中清晰可见，而微孔块状物质具有高暗场信号。另一方面，在吸收数据集中清晰可见的大（可分辨）孔隙，在暗场模态中几乎不可见，因为它们被来自块状物质的暗场信号覆盖。实验还展示了特征的暗场信号如何取决于长度尺度灵敏度，该灵敏度通过相对于光栅干涉仪移动样品来设置。
