Omniprobe 200

Samples were prepared for TEM imaging using Ga focused ion beam (FIB) on Quanta dual beam SEM/FIB (FEI, Hillsboro, OR). Lamellas were lifted out with OmniProbe 200 (Oxford Instruments, Abingdon, United Kingdom) and attached on Omniprobe Lift-out grids (TED PELLA, INC., CA, USA) on the V position to minimize bending of the foil. An ion beam accelerating voltage of 5 keV with a beam current 16 pA was used for the final polish. The average thick ness of each TEM sample is ~50 nm, confirmed by SEM. TEM samples were imaged with a transmission electron microscope (TEM) [Philips CM-20, Hillsboro, OR] with 200 keV using a LaB₆ beam source. Some of the images are taken at a high magnification and patched together to make a montage to retain high enough resolution to resolve dislocation loops. Multiple TEM samples were prepared and observed with different tilts for the composite materials. Dislocation loop areal concentration at each depth was calculated from TEM images (~5 × 5 μm²) divided into 200 × 1800 nm² sections with random tilts. Standard deviation was generated from the accumulated concertation from each section.

The surface of both untreated and treated samples was examined using scanning electron microscopy (SEM, Phenom XL Desktop, Thermo Fisher Scientific, Waltham, MA, USA) to observe the pozzolanic reactivity and visualise crystallised compound formation. An oven-dry sample of less than 10 mm from the UCS test was mounted on an aluminium stub using carbon tape. SEM imaging was taken at 15 KV at 20 μm scale or at 3000× magnification. Additionally, energy-dispersive X-ray spectrometry (EDS, OmniProbe 200, Oxford Instrument, Abingdon, UK) was used to investigate the elemental compositions on the surface of the analysed samples during imaging. Meanwhile, X-ray diffraction (XRD) was used for examining the mineralogy that occurred in the sample before and after the stabilisation process. A similar sample used in SEM was pulverised and scanned using a PANalytical X-ray diffraction spectrometer. The samples were scanned at a 2Ɵ angle with a range of 6° to 90° at 0.02° per step. Through the analysis of variations in the diffraction pattern across different samples, it was possible to detect the shifts in mineralogical composition and gain a better understanding of the underlying physical and chemical processes that have taken place.