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Öğe Durability characteristics of slag based geopolymer concrete modified with crumb rubber(Elsevier Sci Ltd, 2023) Orhan, Taha Yusuf; Karakoc, Mehmet Burhan; Ozcan, AhmetToday, due to the increasing demand in the building sector, the interest of researchers in sustainable building materials is increasing. Geopolymer concretes especially come to the forefront due to energy saving and recycling of waste materials. In this paper, slag based geopolymer concretes were produced by substituting crumb rubber (CR) in different proportions instead of fine aggregate. In the samples using 12 M potassium hydroxide (KOH) as alkali activator, river aggregate was used as aggregate. The 28-day compressive strengths of the samples were between 25.95 MPa and 38.17 MPa, between 9.8 MPa and 11.95 MPa at the end of 300F-T cycles, and between 40.65 MPa and 35.70 MPa in sulfate solutions at the end of 12 weeks. Sulfate (5% Na2SO4 and 5% MgSO4) and freeze-thaw (F-T) (100, 200 and 300 cycles) resistances of the samples cured in the laboratory were determined. As a result of durability tests, the compressive strength, weight changes, sorptivity, water absorption, visual and microstructure analysis of the samples were examined. While the compressive strength of the samples kept in sulfate solutions increased, the compressive strength of the samples exposed to F-T cycles decreased. Sodium sulfate solution caused more strength increase in the samples compared to magnesium sulfate solution. After 300F-T, the strength losses in the samples were over 60%. In general, although the CR slightly reduced the mechanical properties of the control samples, it reduced the permeability of the samples, which increased their durability.Öğe Effect of binder content and recycled concrete aggregate on freeze-thaw and sulfate resistance of GGBFS based geopolymer concretes(Elsevier Sci Ltd, 2021) Ugurlu, Ayse Ilayda; Karakoc, Mehmet Burhan; Ozcan, AhmetThe use of waste materials in concrete production is important because of the recycling of these materials. In this context, the use of both geopolymer binder and recycled concrete aggregate (RCA) becomes important. For this purpose, in this study, ground granulated blast furnace slag (GGBFS) based geopolymer concrete containing RCA was designed and freeze-thaw (F-T) and sulfate resistance of these samples were determined. In the production of geopolymer concrete, three different binder contents (300, 400 and 500 kg/m3) and five different ratios of RCA (0, 25, 50, 75 and 100%) were used. Samples that completed curing period were exposed to 100F-T cycles and two sulfate solutions (3% MgSO4 and 1.5% Na2SO4 + 1.5% MgSO4). Compressive strength, ultrasonic pulse velocity (UPV), weight change and sorptivity values of these samples were determined. At the same time, these results were interpreted together with microstructure analysis (SEM and EDS). An exponential relationship was found between Ca/Si and Si/Al ratios of the samples and their compressive strength. Increasing in Ca/Si ratio and decreasing in Si/Al ratio caused an increase in compressive strength. As the binder content amount increased, the resistance of the samples against F-T cycles and sulfate solutions increased. With the increasing RCA ratio in the samples, there were increases in strength losses, but these losses were low and indicated that RCA was suitable for use in geopolymer concrete production.Öğe Effect of binder dosage and the use of waste rubber fiber on the mechanical and durability performance of geopolymer concrete(Elsevier, 2022) Yolcu, Abdurrahman; Karakoc, Mehmet Burhan; Ekinci, Enes; Ozcan, Ahmet; Sagir, Mehmet AkifThis paper was designed to find solutions to the fact that the availability of natural aggregates in accordance with the standards used in concrete is gradually decreasing, the environmental problems caused by cement threaten our future, and the recycling of used tire waste is very difficult. The effects of three different binder dosages (300, 400 and 500 kg/m(3)) on the mechanical and durability properties of geopolymer concrete (GPC) samples were investigated in binder contents consisting of 98% granulated blast furnace slag (GBFS) and 2% nano silica. As for the aggregate composition, natural sand was used as the fine aggregate, while the waste rubber fibers (WRF) were substituted in different proportions (0%, 5%, 10% and 15%) of the coarse aggregate by volume. Following the solid part was obtained as described, the alkaline activation of GPC specimens was provided using a 12 M NaOH solution. At the end of 28-day curing period, compressive strength, flexural strength, splitting tensile strength, impact resistance, capillary permeability and elevated temperature performance properties were investigated in detail and the results obtained from the mentioned tests were also confirmed by microstructural analysis. Experimental findings revealed that the increase in binder dosage resulted in significant increases in all of the mechanical properties, and it was speculated that this was due to the formation of a denser and more compact microstructure compared to their counterparts produced using lower binder dosage. Besides the negative effects of WRF usage on compressive strength and resistance of elevated temperature, the other performance criteria such as flexural strength, impact resistance and splitting tensile strength values of GPC samples significantly improved with the usage of WRF. As a result, experimental findings demonstrated that the usage of waste rubber fibers in the production of GPC was advantageous in terms of some mechanical and durability properties.Öğe Effect of silica fume and waste rubber on the performance of slag-based geopolymer mortars under high temperatures(Ernst & Sohn, 2023) Sagir, Mehmet Akif; Karakoc, Mehmet Burhan; Ozcan, Ahmet; Ekinci, Enes; Yolcu, AbdurrahmanIn this study, the fire resistance of slag-based geopolymer mortars was investi-gated and the effect of silica fume (SF) and waste rubber (WR) on this resistance was determined. In slag-based geopolymer mortars activated using 12M NaOH solution, 0%, 5%, and 10% by weight SF was substituted for slag; 0%, 5%, 10%, and 15% WR by volume were substituted for fine aggregate. The samples that completed the curing period were exposed to temperatures of 250 degrees C, 500 degrees C, and 750 degrees C for 1 h, and the mechanical (compressive, flexural and splitting tensile strengths, and impact resistance), physical (weight change and sorptivity) and microstructure (scanning electron microscopy [SEM] and energy dispersive spectroscopy [EDS]) properties of these samples were examined. The compres-sive strengths of the samples without WR were between 48.10 and 60.97 MPa, and the samples without SF were between 28.52 and 48.10 MPa. Strength losses at 750 degrees C were between 51.5% and 73.5%. As the SF substitution increased, the samples' mechanical and physical properties improved, whereas as the WR sub-stitution increased, the samples' mechanical and physical properties declined. While the SF substitution had a positive effect on the fire resistance of the sam -ples, the WR substitution had a negative effect. It is thought that the choice of geopolymer binder as a binder in the mortar and the use of waste tires as aggre-gate contribute to the literature in terms of both preventing environmental pollution and ensuring the recycling of these materials.Öğe Effects of elevated temperatures on the properties of ground granulated blast furnace slag (GGBFS) based geopolymer concretes containing recycled concrete aggregate(Taylor & Francis Ltd, 2022) Topal, Ozge; Karakoc, Mehmet Burhan; Ozcan, AhmetThe use of waste materials in concrete design draws the attention of researchers. Studies on the use of these materials both as binders and aggregates accelerate. In this study, ground granulated blast furnace slag (GGBFS) based geopolymer concrete was produced. 0, 25, 50, 75 and 100% recycled concrete aggregate (RCA) was used instead of river aggregate in the mixtures. These samples were exposed to temperatures at 100, 200, 400, 600 and 800 degrees C. The cooling process of these samples exposed to temperature was in 3 different forms: air, oven and water. Compressive strength, ultrasonic pulse velocity (UPV), weight loss, sorptivity and water absorption values of the samples were determined. At the same time, the changes in the microstructure of the samples under the elevated temperature were examined. Compressive strengths of the samples decreased with increasing RCA ratio in the mixture. Samples were severely affected due to elevated temperature, properties of the samples decreased. As the temperature degree increased, the weight loss and sorptivity values of the samples increased. As the temperatures to which the samples were exposed increased, there was a decrease in Ca/Si ratio and an increase in Si/Al ratio. The microstructure of the samples deteriorated at elevated temperatures.Öğe Evaluation of sulfate and salt resistance of ferrochrome slag and blast furnace slag-based geopolymer concretes(Ernst & Sohn, 2019) Ozcan, Ahmet; Karakoc, Mehmet B.In this study, mechanical, visual, and microstructure changes of geopolymer concrete exposed to sulfate and salt effects were investigated. Elazig ferrochrome slag (EFS) and blast furnace slag (BFS)-based geopolymer concretes which completed curing time were immersed in 5% sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), sodium chloride (NaCl), and magnesium chloride (MgCl2) solutions for 12 weeks. The compressive strength values, ultrasonic pulse velocities, visual inspections, weight, and length changes of the samples were determined in this investigation. In addition, scanning electron microscopy was performed for the microstructure analysis of the samples removed from the solutions. Sulfate solutions had a more negative effect on the samples than salt solutions. As the EFS ratio in the mixture increases, the loss rate in the strength of the samples exposed to sulfate and salt solutions decreased. While samples exposed to sodium chloride, sodium sulfate, and magnesium sulfate solutions occurred weight gain, samples exposed to magnesium chloride occurred weight loss. The samples in salt solutions shrank, while the samples in sulfate solutions expanded. No deterioration occurred on the surfaces of the samples exposed to the solutions for 12 weeks.Öğe Investigation of the properties of two different slag-based geopolymer concretes exposed to freeze-thaw cycles(Ernst & Sohn, 2019) Ozdal, Mustafa; Karakoc, Mehmet Burhan; Ozcan, AhmetFerrochrome slag (FS) and ground granulated blast furnace slag (GGBFS) were used as resource material in geopolymer concrete mixtures. A mixture of 10 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used as the activator. After the two different slag-based geopolymer concrete (SGC) mixtures were prepared and molded. They were kept at 80 degrees C for 24 hr, and then the SGC samples were cured in 23 +/- 1 degrees C water for 27 days. Samples that completed the curing times were exposed to the 300 freeze-thaw (F-T) cycles. The compressive strength, ultrasonic pulse velocity, relative dynamic elasticity modulus values, weight changes, and appearances of the SGC samples were examined at the end of every 50 F-T cycles. Scanning electron microscopy analysis was performed to examine the microstructure changes of the samples after 300 F-T cycles. As the GGBFS proportion in the SGC mix increased, the mechanical properties of the samples against the F-T effect increased. Samples containing 100% FS and 75% FS fell apart at the end of 150 and 200 F-T cycles, respectively. The deterioration of the geopolymer gel structures of the samples exposed to F-T was decreased with increasing GGBFS ratio in the mix.Öğe Performance of glass powder substituted slag based geopolymer concretes under high temperature(Elsevier Sci Ltd, 2022) Derinpinar, Aslihan Nida; Karakoc, Mehmet Burhan; Ozcan, AhmetGeopolymer concretes provide advantages in terms of recycling waste materials. Geopolymer concretes are advantageous in terms of both limiting the use of Portland cement and recycling waste materials. In this study, 5 different geopolymer concrete mixture groups were prepared by replacing slag with 0.5%, 10, 15 and 20% by weight glass powder (GP). Geopolymer concrete samples prepared by using 12 M sodium hydroxide solution as an alkali activator were cured in the laboratory environment. The samples, which completed their curing pe-riods, were kept at 150, 300, 450, 600 and 750 C temperatures for 1 h. Compressive strength, weight change and sorptivity values of these samples were determined. These results were interpreted together with the visual inspections and microstructure analyzes (SEM and EDS) of the samples. As the GP substitution rate increased, the mechanical properties of geopolymer concretes decreased. However, GP improved the performance of geo-polymer concretes exposed to high temperatures. Cooling in air affected the samples less negatively than cooling in water. While the Ca/Si ratios of the samples decreased at 450 C and above, the Si/Al ratio increased.Öğe The Resistance of Blast Furnace Slag- and Ferrochrome Slag-Based Geopolymer Concrete Against Acid Attack(Springer International Publishing Ag, 2019) Ozcan, Ahmet; Karakoc, Mehmet BurhanIn this study, blast furnace slag- (BFS) and Elazig ferrochrome slag (EFS)-based geopolymer concretes were produced. Samples were immersed in 5% phosphoric acid (H3PO4), hydrochloric acid (HCl), hydrofluoric acid (HF) and sulfuric acid (H2SO4) solutions for 12 weeks. The compressive strengths, ultrasonic pulse velocities, weight and length changes of the samples were determined in this process. At the same time, visual inspections of the samples were investigated. Scanning electron microscopy (SEM) analysis was performed for the microstructure analysis of the samples removed from the solutions. 5% H2SO4 solution had the most negative effect on the samples. As the EFS ratio in the geopolymer concrete mixture increased, the loss rate in the strength of the samples exposed to acid solutions decreased. H3PO4 solution caused less weight loss in samples than other acid solutions. It was seen that the samples immersed in H3PO4 and HCl solutions shrank and that the samples immersed in HF and H2SO4 solutions expanded. Softening, cracking and corruption occurred on the surfaces of the samples exposed to the acid solutions for 12 weeks. With increasing EFS ratio in the mixture, the deterioration of the samples' surfaces exposed to acid solutions decreased. Ettringite formations were seen in the SEM images of geopolymer concretes immersed in 5% H2SO4 solution.
