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    Eco-Geopolymers: Physico-Mechanical Features, Radiation Absorption Properties, and Mathematical Model
    (Mdpi, 2022) Dogan-Saglamtimur, Neslihan; Bilgil, Ahmet; Erturk, Sefa; Bozkurt, Vakkas; Suzgec, Elif; Akan, Arife Gozde; Nas, Pervin
    Waste ashes and radiation are hazardous environmental and health factors; thus, a lot of attention is paid to their reduction. We present eco-geopolymer building materials (GPBMs) based on the class F fly ashes (FFAs) from thermal power plants (TPPs) and their implementation as a barrier against radioactive radiation. Different methods of production, ratios of FFA to alkali activator, and temperatures of curing were tested. Small spherical particles and higher content of SiO2 resulted in developed surface area and higher reactivity of Isken TPP FFA than Catalagzi TPP FFA. Lower activator concentration (10% vs. 20%) and curing temperature (70 vs. 100 degrees C) caused an increase in GPBM compressive strength; the highest value was measured as 93.3 MPa. The highest RA was measured for GPBMs, provided alkali activator ratio (Na2SiO3/NaOH) was >2 and its concentration was 20%. The mathematical model developed in this study proved FFA quantity, and thus GPBM mechanical properties, as key factors influencing RA. In the light of these results, the lightweight GPBMs can be excellent materials for the construction sector dedicated to immobilization, storage, and disposal for radionuclides or barriers against radiation; however, multiple steps of their production require careful optimization.
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    Geopolymer's radiation absorption detected by Geiger-Muller counter
    (Iop Publishing Ltd, 2019) Suzgec, Elif; Dogan-Saglamtimur, Neslihan; Bozkurt, Vakkas; Erturk, Sefa
    Fly ash (FA), which is an industrial solid waste released by the burning of coal in thermal power plants, is responsible for causing environmental problems. Radiation is also an environmental problem besides causing health problems for human being. Geopolymer is a specialized building material resulting from the reaction of a source material, which is rich in silica and alumina, with alkaline solution. It is ordinary Portland cement (OPC) free building material. It has been reported that geopolymer building material has good engineering properties with a reduced carbon footprint resulting from the total replacement of OPC as greener alternative. In this study, it is aimed to measure radiation absorption of geopolymers produced from the reaction of FA, which was supplied from Isken Sugozu Thermal Power Plant (Adana, Turkey) and rich in silica and alumina in total content of 83.74, with alkaline activators (sodium hydroxide and sodium silicate) at curing temperatures (70 degrees C and 100 degrees C). In the study, lattice measurement system consisting of nested lead plates to avoid unwanted radiation was designed to determine radiation absorption of geopolymers. By using this new system, geopolymer was found to be 5% better radiation absorption capacity than OPC building material when it is compared.
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    Production of geopolymer composites by using different alkaline solution/material ratio
    (Iop Publishing Ltd, 2019) Dogan-Saglamtimur, Neslihan; Oz, Hatice Oznur; Bilgil, Ahmet; Suzgec, Elif; Vural, Turkan
    This study reports an experimental program to optimize mix design parameters of fly ash-based geopolymer engineering composites. Fly ash (FA) supplied from Catalagzi Thermal Power Plant (Zonguldak, Turkey) and Rilem Cembureau Standard Sand were used together with a constant ratio of 0.50 for producing geopolymer. In the first step, two different alkaline solution/material ratio (FA+standard sand) (L/M) were determined as 0.20 and 0.40, respectively. After that, sodium silicate ((Na2SiO3) and 12M sodium hydroxide (NaOH) were utilized at a ratio of 1, 2, and 3, respectively. 6 mixtures obtained by using different design parameters were cured at 70 degrees C for 24 hours, respectively, and then they were stored at room temperature until testing age. While the physical properties of the samples were measured by the bulk density and water absorption tests at 28 days, mechanical properties were tested via the compressive and flexural strength tests at 90 days, respectively. The results indicated that the highest compressive strength for geopolymer materials was found as 36.5 MPa in the mixture produced with the ratios of L/M=0.2 and Na2SiO3/NaOH=2 (by weight). However, less alkali reaction caused by using excessive activator solutions decreased the strength characteristics of geopolymer.