2.2. Nano-XCT Study

Laboratory X-ray microscopy data of a cement sample were obtained using an Xradia nXCT-100 instrument (Xradia, Pleasanton, CA, USA)—Figure 1. This transmission X-ray microscope (TXM) consists of a rotating anode as an X-ray source (Cu-Kα radiation, 8 keV photon energy), a capillary condenser optic, a Fresnel zone plate (FZP) as an objective, and a scintillator/CCD detector system. In the full-field imaging mode, the field of view (FOV) is 65 µm × 65 µm, resulting in a pixel size of 65 nm for camera binning 1 (1024 × 1024 pixels). This setup provides an almost parallel-beam geometry. Therefore a 180° rotation is sufficient for (XCT). A tomography tilt series of 601 images was recorded within an exposure time per image of 120 s. 3D tomographic reconstruction is performed with the standard Xradia software package XMReconstructor 9.0.

Scheme of the nano-XCT experiment.

The sample was prepared by chipping off a smaller piece of 40 to 80 µm to meet the transmission requirement of the cement-based material for 8 keV and to fit the FOV. Manipulation with the sample as preparing, selecting, mounting, and marking with a gold bead (1.5–3 µm size, Alfa Aesar) was performed under an optical microscope. The sample was fixed on the holder with the Gorilla super glue (Gorilla Glue, Inc., Cincinnati, OH, USA).

The size of the observed volume was 65 × 65 × 65 µm³. In Figure 2b, one can distinguish four components: cement material, capillary pores, and two filler grains: multiple brighter grains and one large dark grain.

(a) Observed zone of the sample—Region of Interest (ROI)—red box, (b) Example of the virtual cross-sections in all three dimensions—XY, YZ and XZ.