The Influences of Neutron Irradiation on Aggregate Induced Degradation of Concrete

Abstract

December 10, 2018 Characterization of mineral aggregatesNatural rocks may contain traces of other phases distinct from their main mineralogical components. Macroscopic observations of natural samples of albite, anorthite, almandine and dolomite suggest that they are impure. To characterize the purity of the samples, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), x-ray diffraction (XRD), and Raman spectroscopy were employed, as described below. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS)Energy dispersive X-ray spectroscopy (EDS) is an analytical technique that can be coupled with scanning electron microscopy (SEM). SEM-EDS can be used for elemental analysis and chemical characterization of different areas on a sample surface, with a resolution that is on the order of a few microns.[4] The working principle of EDS relies on the interaction between X-rays and the atoms on the sample surface. To stimulate characteristic X-rays from a specimen, highenergy electrons are focused on the sample, and the incident beam excites electrons in the inner shell of an atom, creating an electron hole that is then filled by electrons in the outer shell, releasing energy in the process. The amounts and energies of X-rays emitted from the sample are measured by a spectrometer to create a unique emission spectrum depending on the atomic structure.[5] Prior to SEM measurements, selected mineral samples were powdered to few micrometers in size using a ball mill, and then coated with Au for 1 minute using a Hummer® 6.6 Sputter Coater, producing a film with thickness of about 6-7 nanometers. SEM imaging was carried out using secondary electrons and backscattered electrons using a FEI Nova NanoSEM 230 (7 kV, 80 pA). X-ray Diffraction (XRD)Selected samples were analyzed using powder X-ray diffraction (XRD) to identify the crystalline phases that are present.[6] The pristine mineral samples were ball milled to produce particles that are a few micrometers in size. XRD patterns were recorded using a Bruker D8-Advance powder X-ray diffractometer in θ-θ Bragg-Brentano geometry, using Cu Kα radiation (λ = 1.5406 Å), 40 kV accelerating voltage, and 40 mA beam intensity. A 2θ range of 10° to 70°, a 2θ scan step size of 0.02°, and an exposure time of 0.5 seconds per step were employed. The peak locations and relative peak intensities in the X-ray diffractograms provide information on the particular crystalline compounds that are present in the sample. Raman SpectroscopyRaman spectroscopy is a technique for measuring the vibrational and rotational molecular bonding in a system. [7] Therefore, Raman spectroscopy was applied to observe structural changes in the mineral samples after ion-implantation. Similar to SEM-EDS and XRD, Raman spectroscopy also provides a fingerprint spectrum for the species present in a sample.[8] The working principle for Raman analysis relies on both elastic (Rayleigh) and inelastic (Raman) scattering of a laser beam. A monochromatic laser of wavelength near th...