Revealing 3D orientation and strain heterogeneity in calcite generated by bio-cementation

Abstract

Bio-cementation uses bacterially induced calcite to bind sand grains, offering a low-carbon approach to soil stabilization. However, the 3D morphology, orientation texture, and internal strain states of individual calcite bonds remain insufficiently characterized. Here, we combine computed micro-tomography, 3D X-ray Diffraction (3DXRD), and Dark-Field X-ray Microscopy (DFXM) to nondestructively characterize grain morphology, crystallographic orientation, and both type II (intergranular) and type III (intragranular) elastic strains in calcite formed at sand-sand contacts during bio-cementation. Tomography establishes the sample morphology and the cemented contact architecture; 3DXRD provides grain-averaged orientation and strain states; and DFXM resolves sub-grain misorientations and localized strain concentrations generated during growth with 100 nm resolution. The combined results show that calcite precipitation through bio-cementation produces anisotropic internal strain and distinct sub-domain structures that can influence bond integrity and load transfer at the macroscopic scale.

Figures (11)

• Figure 1: (a) Schematics of 3DXRD setup. A box beam illuminates the region of interest in the sample. A 2D detector then collects diffraction coming from individual grains as a function of the rotation angle $\omega$. The peaks are then indexed, their positions and relative size and strain are measured, and (b) Schematics of the DFXM setup. A parallel or line beam illuminated the region of interest in the sample. Images of one diffracted lattice plane for one grain of interest (highlighted in green) are collected in function of the tilt motors $\omega$ and $\chi$ for mosaicity measurements, as well as the 2$\theta$ angle for strain measurements. In both figures, the sand is represented in yellow and the calcite in purple.
• Figure 2: 3D rendering of the volumes acquired with tomography of: (a) S1, and (b) S2, showing the concentrated beam at the contact for the 3DXRD measurement.
• Figure 3: (a) 3D plot showing the indexed sand and calcite grains from 3DXRD (colored by IPF-x). Axes values are centered around the center of the incoming beam, (b) the segmented mid-layer tomography slice from the illuminated volume for 3DXRD (white: calcite, yellow: sand), (c) the IPFs for the calcite crystals along the laboratory x, y and z directions, and (d) the IPFs for the quartz crystals along the laboratory x, y and z directions.
• Figure 4: Overlay of the reconstructed calcite crystals from 3DXRD (colored by grain ID) and the reconstructed illuminated calcite volume from tomography. Refer to \ref{['sec:3dxrdpbs']} for the explanation behind missing regions in the 3DXRD reconstruction.
• Figure 5: (a) Histogram of the relative strain of the calcite crystals along the c-axis (in crystal frame), and (b) 3D plot showing the indexed calcite grains from 3DXRD, colored by the volumetric strain. Image shows with display range between -6$\times 10^{-4}$ and 6$\times 10^{-4}$ for visualization purposes. The raw volumetric strain data ranged between -1.6$\times 10^{-3}$ and 3$\times 10^{-3}$.