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    Gamma and neutron attenuation properties of alkali-activated cement mortars
    (Pergamon-Elsevier Science Ltd, 2020) Ozturk, Buket Canbaz; Kızıltepe, Cavit Cağatay; Ozden, Banu; Guler, Erkan; Aydin, Serdar
    Radiation-shielding properties of alkali-activated cement (AAC) mortar mixtures prepared using different precursors such as ground granulated blast furnace slag (GGBFS), fly ash (FA), metakaolin (MK) and waste clay material containing boron (WCB) were investigated comparatively with Ordinary Portland Cement (OPC) mixture. The gamma linear attenuation coefficients of the mixtures were determined both experimentally and theoretically. The experimental coefficients of the mixtures were measured with NaI(Tl) detection system for gamma energies of Cs-137 (662 keV) and Co-60 (1173 and 1332 keV) and the gamma transmission parameters (half-value layer, HVL; tenth-value layer, TVL and mean free path, MFP) were determined using these coefficient values. The theoretical coefficients of the mixtures were calculated using XCOM software for the energy range of 10-3000 keV. In addition, neutron attenuation coefficients of the mortar mixtures were theoretically calculated with the NCNR computation software for thermal (0.025-1 eV), slow (1-10 eV), resonance (10-300 eV), intermediate (300 eV-1 MeV) and the fast neutrons (1 MeV-20 MeV). Test results indicated that GGBFS and FA based alkali-activated cement mortars had similar gamma attenuation properties to the OPC mortar while the WCB and MK-incorporating AAC mixtures had slightly worse properties in this respect. In terms of thermal and slow neutron shielding properties only AAC mixtures containing WCB showed significantly better behaviour compared to OPC. For neutrons having higher energy levels than slow neutrons, all AAC and OPC mortar mixtures showed comparable properties.
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    Valorization of Boron Mine Tailings in Alkali-Activated Mortars
    (Asce-Amer Soc Civil Engineers, 2019) Aydin, Serdar; Kızıltepe, Cavit Cağatay
    Mine tailings cause significant storage and environmental problems because a large amount of tailings containing potentially numerous hazardous contaminants is generated during mining operations. Therefore, the utilization of mine tailings in different sectors should be taken into consideration to minimize the storage efforts and environmental pollution problems. In this two-stage study, the alkali activation opportunity of waste clay containing boron (WCB) discarded from boron mine production was investigated. In the first stage of this study, alkali activation of WCB calcined at different temperatures between 500 degrees C and 800 degrees C was investigated under steam-curing conditions. It was found that a calcination temperature of at least 700 degrees C is necessary to initiate the alkali activation of WCB, whereas the maximum compressive strength value was obtained at 800 degrees C. Subsequently, the effects of alkaline activator solution type (sodium hydroxide and sodium silicate) and quantity on the development of engineering properties of alkali-activated WCB mortars, such as compressive and flexural strength, water sorptivity, and drying shrinkage, were investigated by using WCB calcined at 800 degrees C. Furthermore, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA/DTA), and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analyses were carried out on the hardened paste mixtures. The minimum activator concentration for alkali activation of calcined WCB was 6% Na2O by weight of WCB with a minimum silicate modulus (Ms=SiO2/Na2O) of 1.2. A compressive strength value up to 38 MPa along with acceptable water absorption characteristics and drying shrinkage values can be obtained from alkali activation of calcined WCB at 800 degrees C. NaOH activator was not as effective as sodium silicate activator in activating WCB, even in high dosages.