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    Effect of waste travertine powder on properties of rhyolitic tuff-based geopolymer
    (Elsevier, 2024) Tekin, Ilker; Pekgoz, Mahfuz; Dirikolu, Irem; Kiamahalleh, Mohammad Valizadeh; Gholampour, Aliakbar; Gencel, Osman; Ozbakkaloglu, Togay
    This investigation explores the potential of geopolymer technology as an eco-friendly substitute for conventional construction materials by emphasizing the innovative use of naturally occurring green rhyolitic tuff and repurposed travertine powder in geopolymer paste formulations. Replacement levels of tuff with travertine at 40 %, 45 %, and 50 %, along with an alkaline solution with a NaOH molarity range of 8.2 M-22.1 M, have been analyzed for their impact on flowability, water absorption, porosity, compressive strength, and unit weight of the geopolymers over curing periods of 2, 28, and 90 days. The flowability measurements show that adding 40 %, 45 %, and 50 % travertine leads to approximately 7 %, 31 %, and 31 % reductions in the flowability of the geopolymer, respectively. It is demonstrated that adding 40 % travertine significantly improves the geopolymers' compressive strength with an 11.5 M NaOH concentration, showing substantial increases of approximately 15.5, 9.0, and 2.4 times at the curing duration of 2, 28, and 90 days, respectively, relative to the geopolymer without travertine. As an optimum points, an 18.5 M NaOH and an 0.7 solution-to-powder ratio decrease the long-term apparent porosity and water absorption of the geopolymer without travertine by about 14 % and 19 % compared to those at the same solution-to-powder ratio with 11.5 M NaOH, respectively. Microscopic examinations were employed to validate the development of sodium aluminosilicate hydrate, calcium aluminosilicate hydrate, and calcium silicate hydrate gels, underscoring the advantageous contribution of the elevated CaO content in the travertine to the geopolymer matrix. This research not only highlights the environmental benefits of repurposing waste materials but also contributes to the development of more sustainable and durable geopolymer pastes, offering a promising approach to enhancing environmental stewardship in material science practices.
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    The effects of ZnO powder and different fiber types used in tuff/calcite-based geopolymers on electromagnetic shielding effectiveness
    (Elsevier, 2024) Tekin, Ilker; Pekgoz, Mahfuz
    Electromagnetic (EM) shielding has become increasingly important in our modern world due to the growing use of electronic devices, which poses risks of EM pollution and its adverse effects on humans. Many studies have explored the incorporation of various additives into geopolymer mixes to enhance their EM shielding properties. This study investigates the impact of tuff/calcitebased geopolymers reinforced with three different types of fibers (Polypropylene, Steel, and Carbon) and varying percentages (2.5 %, 5 %, and 10 %) of ZnO powder on EM shielding effectiveness. Compressive strength, flexural strength, water absorption, length change tests, and EM shielding (900-6000 MHz at every 100MHz step) measurements were performed on geopolymer samples. Optimal shielding performance was achieved by the addition of 10 % ZnO by volume alongside carbon fiber. This combination resulted in a total shielding value of -78.92dB at a bandwidth of 2800MHz.
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    Investigation of electromagnetic interference shielding performance of ultra-high-performance mortar incorporating single-walled carbon nanotubes and steel fiber
    (Elsevier, 2024) Subasi, Serkan; Seis, Muhammet; Tekin, Ilker; Kazmi, Syed Minhaj Saleem; Munir, Muhammad Junaid; Gencel, Osman; Ozbakkaloglu, Togay
    For security amenities and key infrastructure, construction materials with extraordinary mechanical, durability, and electromagnetic interference (EMI) shielding performance are essential. This study investigates the EMI shielding performance of ultra-high performance mortar (UHPM) incorporating single-walled carbon nanotubes (SWCNT) and steel fibers. Currently, no such work is present in the existing literature. Eight mixtures were prepared with varying SWCNT dosages (0%-0.03 % by weight of cement) and steel fiber additions (1.2 % of the volume of the UHPM mixture). The performance of UHPM incorporating SWCNT and steel fibers was evaluated through flow diameter, compressive strength, flexural strength, Schmidt hardness, ultrasonic pulse velocity, EMI shielding performance, and scanning electron microscopy analysis tests. It is observed that increasing the SWCNT content enhances the compressive strength, flexural strength, ultrasonic pulse velocity, and Schmidt hardness of UHPM. The addition of steel fibers further enhances compressive (up to 22 %) and flexural (up to 92 %) strengths. In terms of the transmittance behavior, the improved EMI shielding performance of UHPM with the increasing SWCNT content is observed prominently at high electromagnetic frequencies (i.e., 2500 MHz-5100 MHz). However, the improved shielding performance is observed to be quite low, limited to 10 dB. Moreover, combining steel fibers and SWCNT enhances the EMI shielding performance of UHPM in terms of the transmittance behavior. As a result, UHPM incorporating SWCNT and steel fibers behaves as an absorbent material, shielding a significant amount of energy, approximately 45 dB, at a frequency of 5000 MHz. Based on the results, UHPM incorporating SWCNT and steel fibers can be used effectively as EMI shielding material. The findings of this study will enhance the practical applications of UHPM incorporating SWCNT and steel fibers.
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    Microstructural investigation and strength properties of structural lightweight concrete produced with Zeolitic tuff aggregate
    (Elsevier, 2021) Pekgoz, Mahfuz; Tekin, Ilker
    In this study, physical, mechanical, and microscopic investigations were carried out on structural lightweight concretes (LWC) produced with zeolitic aggregate. Zeolitic tuff aggregate, 300 kg/m(3), and 400 kg/m(3) dosages OPC and 0.70 and 0.45 water/cement ratios were used in LWC productions. An optical microscope method was used to determine the aggregate-cement interface zone (ITZ) on the hardened LWC. SEM analyses were performed on the specimens to determine microstructural properties as well. Moreover, water absorption, capillary suction, and compressive strength tests were carried out. The experimental results showed that ITZ thickness and compressive strength are significantly depend on the cement dosage and w/c ratio in structural LWC. ITZ thicknesses were measured 20-33% less in LWC produced with a 0.45 w/c ratio and the 400 kg/m(3) cement dosage. On the SEM analyses, dense CH and ettringite formations were observed at the early age of all LWC in high w/c ratios. However, on the 28th day, well-formed CSH structures were observed in large areas with lower w/c ratios.
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    A novel approach to finding optimum operating conditions of design factors for the grinding experiment
    (Taylor & Francis Inc, 2021) Ucurum, Metin; Ozdemir, Akin; Teke, Cagatay; Tekin, Ilker
    The efficiency of grinding experiments is an important issue for many industries. In this paper, a central composite design-based methodology was proposed to investigate the four design factors that affect the particle sizes. The four design factors were specified as mill speed (% of N-c ), ball filling ratio (f(c) ), powder filling ratio (j(b) ) and grinding time (min). Another important issue was how to obtain an optimum operating condition for four design factors. For this particular purpose, a novel dual response optimization model was proposed using the particle sizes (d (10), d (50), and d (90)) and the span value concept. This proposed approach was compared to the desirability function-based optimization concept. The verification study of the experiment was also carried out. The results of the grinding experiment runs showed that the optimum operating conditions were mill speed 73.495% of N-c , ball filling ratio 0.354, powder filling ratio 0.157, and grinding time 70 min. In addition, d (10), d (50), and d (90) were found 3.31 mu m, 12 mu m, and 45.6 mu m, respectively. The span value was also found at 3.52.
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    Properties of Lightweight Concrete Blocks with Waste Zeolitic Tuff
    (Kaunas Univ Tech, 2020) Tekin, Ilker; Kotan, Turkay; Osmanson, Allison T.; Brostow, Witold; Gencel, Osman; Martinez-Barrera, Gonzalo
    In general, three different types of wall products commonly used in the building sector, namely traditional clay brick, lightweight concrete blocks and aerated concrete, contain pumice and perlite. We have created alternative block walls with Bayburt stone (BS) containing zeolite, namely lightweight concrete masonry blocks (LCMBs). BS was an aggregate, cement dosages ranging from 150 to 250 kg/m(3) were a binder, 3 different type of superplasticizers were selected as a chemical additive. Compressive strength, water absorption, unit weight, elevated heat effect, freeze-thaw resistance, capillary water absorption and thermal conductivity tests were performed. Compressive strength and freeze-thaw resistance of LCMBs are higher than the respective values for the other traditional wall products - with less amount of cement usage. Compressive strength values of lightweight concretes (LCs) were between 4 MPa and 9 MPa on the 3rd day, unit weights of the LCs were between 1.43 and 1.60 kg/dm(3), thermal conductivity values of the so produced block wall elements were approximate to 0.55 W/mK.
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    Recycling zeolitic tuff and marble waste in the production of eco-friendly geopolymer concretes
    (Elsevier Sci Ltd, 2020) Tekin, Ilker; Gencel, Osman; Gholampour, Aliakbar; Oren, Osman Hulusi; Koksal, Fuat; Ozbakkaloglu, Togay
    The use of waste-based materials as cement alternative in concrete has recently received significant attention for the development of an eco-friendly construction material. The aim of the study reported in this paper is to develop a sustainable composite using waste products and natural fibers to reduce the environmental impact associated with cement production and extraction of non-renewable natural aggregates. Therefore, in this paper, an experimental study on the properties of alkali-activated composite that was manufactured with zeolitic tuff and marble waste is presented. Cotton and viscon fibers were also added to the composites to investigate the effect of crack bridging on the behavior of natural fiber-reinforced geopolymer composites with 5 M and 10 M sodium hydroxide (NaOH). The results show that geopolymers prepared with 10 M NaOH exhibit a higher compressive strength (53-371% at 28 days), elastic modulus (25-343% at 28 days), dry density (2-13%), and thermal conductivity (1-20%), a lower water absorption (1-35% at 28 days) and apparent porosity (1-30%), and a nearly similar flexural strength compared to those prepared with 5 M NaOH. It is also found that viscon fiber-reinforced geo-polymers experience a higher compressive strength, elastic modulus and thermal conductivity, but a lower dry density than cotton fiber-reinforced geopolymers. These results are promising and point to the significant potential of the simultaneous use of zeolitic tuff and marble waste as cement replacements together with natural fibers as crack bridging material to develop an eco-friendly composite, which contributes toward reducing the carbon dioxide emission associated with the cement production and eliminating the environmental effect of abundant waste-based materials. (C) 2020 Elsevier Ltd. All rights reserved.