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Öğe Enhancing acid resistance of geopolymer concrete composites by utilising styrene-butadiene latex, nano-silica and micro-silica powder(Taylor & Francis Ltd, 2023) Kantarci, Fatih; Turkmen, Ibrahim; Ekinci, EnesThe acid resistance of geopolymer binder, a promising alternative to ordinary Portland cement with clean technology option, needs detailed investigations for widespread use in different applications and severe acidic conditions. The aim of this work is to enhance acid resistance of geopolymer concretes (GPCs) by employing styrene-butadiene latex (SBL), nano-silica (NS) and micro-silica (MS) powders. The residual compressive strength, weight loss, visual appearance and microstructure properties of GPC samples were evaluated after exposed to hydrochloric acid (HCl) solutions with different concentrations (3%, 5% and 7%) for 90 and 180 days. The addivites increase residual compressive strength by preventing acid liquids to ingress the interior areas thanks to additional pozzolanic and filler effect leading to more compact and denser microstructure. Any apparent damage was not observed at the outer surface of GPC specimens.Öğe Fire resistance of geopolymer concrete produced from Elaz ferrochrome slag(Wiley, 2016) Turkmen, Ibrahim; Karakoc, Mehmet Burhan; Kantarci, Fatih; Maras, Muslum Murat; Demirboga, RamazanThis paper presents the effect of elevated temperatures up to 700 degrees C on compressive strength and water absorption of two alkali-activated aluminosilicate composites (one of them is river sand aggregate geopolymer concrete; the other one is crushed sand aggregate geopolymer concrete) and ordinary Portland cement based concretes. To obtain binding geopolymer material, Elaz ferrochrome slag was ground as fine as cement, and then it was alkali activated with chemical (NaOH and Na2SiO3). Geopolymer concrete samples were produced by mixing this binding geopolymer material with aggregates. At each target temperature, concrete samples were exposed to fire for the duration of 1h. Fire resistance and water absorption of geopolymer and ordinary Portland cement concrete samples were determined experimentally. Experimental results indicated that compressive strength of geopolymer concrete samples increased at 100 degrees C and 300 degrees C temperatures when compared with unexposed samples. In geopolymer concrete samples, the highest compressive strength was obtained from river aggregates ones at 300 degrees C with 37.06MPa. Water absorption of geopolymer concrete samples increased at 700 degrees C temperature when compared with unexposed samples. However, a slight decrease in water absorption of concrete samples was observed up to 300 degrees C when compared with unexposed samples. SEM and X-ray diffraction tests were also carried out to investigate microstructure and mineralogical changes during thermal exposure. Copyright (c) 2016 John Wiley & Sons, Ltd.Öğe Fire Resistance of Geopolymer Concrete Produced From Ferrochrome Slag by Alkali Activation Method(Ieee, 2013) Turkmen, Ibrahim; Karakoc, Mehmet Burhan; Kantarci, Fatih; Maras, M. Murat; Demirboga, RamazanThe effect of high temperatures up to 700 degrees C on compressive strength and water absorption of two alkali-activated aluminosilicate composites (one of them with river sand aggregates, the second crushed sand aggregates) and ordinary Portland cement (OPC) concretes is analyzed in this paper. Binding geopolymer material was obtained after grinding the Elazig Ferrochrome slag (EFS) as fine as cement and alkaline activating with chemical materials (NaOH-Na2SiO3). Geopolymer concrete samples were produced by using this binding material with aggregates. Produced concrete samples were exposed to temperature for 1 hour, after reaching the maximum temperature. Fire resistance and water absorption of geopolymer and OPC concrete samples was obtained experimentally. Compressive strength of river aggregates and crushed sand aggregates concrete increased at 100 and 300 degrees C temperatures compared to unexposed samples, and the maximum compressive strength for these geopolymer concrete sample was obtained at 300 degrees C. Water absorption of all concrete samples increased at 700 degrees C temperature compared to unexposed samples. But there appeared to be a slight decrease of water absorption in the all concrete samples up to 300 degrees C temperatures compared to unexposed samples. Scanning electron microscopy and XRD tests were also conducted to examine microstructure and mineralogical changes during the thermal exposure.Öğe The improvement of mechanical, physical and durability characteristics of volcanic tuff based geopolymer concrete by using nano silica, micro silica and Styrene-Butadiene Latex additives at different ratios(Elsevier Sci Ltd, 2019) Ekinci, Enes; Turkmen, Ibrahim; Kantarci, Fatih; Karakoc, Mehmet BurhanThis study aims to the improvement of volcanic tuff-based geopolymer concrete (GPC) with the addition of nano silica (NS), micro silica (MS) and Styrene-Butadiene Latex (SBL) at the different ratios. For this purpose, incorporating of volcanic tuff with NS (1, 2, 3%), MS (1, 3, 5%) and SBL (5, 10, 15%) was provided. GPC samples were produced with two different activation method (Na2SiO3 + NaOH and sole NaOH). 28-day compressive strength, freeze-thaw (FT) resistance, microstructure, water absorption, density, bulk density and apparent porosity values of volcanic tuff-based GPC samples were investigated. The results indicated that the compressive strength of NaOH-activated samples was much higher than similar ones activated with Na2SiO3 + NaOH. In both activation methods, the optimum NS and SBL ratios were determined as 2% and 5%, respectively. Also, the optimum additive of MS ratio was determined 5% and 3% for Na2SiO3 + NaOH and sole NaOH-activated samples, respectively. As well as the highest compressive strength losses as a result of 300 FT cycles were observed in pure samples for both activation methods, Na2SiO3 + NaOH-activated samples exhibited better resistance to FT effect than similar ones activated with sole NaOH. (C) 2018 Elsevier Ltd. All rights reserved.Öğe Improving elevated temperature performance of geopolymer concrete utilizing nano-silica, micro-silica and styrene-butadiene latex(Elsevier Sci Ltd, 2021) Kantarci, Fatih; Turkmen, Ibrahim; Ekinci, EnesGeopolymer binders (GPBs) have gained an increasing research potential in recent years due to their environmental, economic and durability advantages. This paper aims to improve elevated temperature performances of volcanic tuff (VT) based geopolymer concrete (GPC) by utilizing nano-silica (NS), micro-silica (MS) and styrene-butadiene latex (SBL). To this end, NS, MS and SBL additives were added to GPC samples at 2%, 2% and 5% ratios by weight of binder, respectively. GPB was obtained by activating ground VT with 12 M NaOH solution. Produced GPC samples were exposed to elevated temperatures (100, 300, 500 and 700 degrees C) for 1 h after reaching the target temperature. Changes in compressive strength, water absorption, visual appearance, weight and microstructure of GPC samples were investigated after the influence of elevated temperatures. The experimental findings displayed that compressive strength of GPCs increased up to 300 degrees C independently of the type of additive used, but higher temperatures than 300 degrees C caused decrease in compressive strength values. As a result of mechanical tests and microstructure investigations, it was determined that MS additive significantly increased the elevated temperature performance of GPCs. Additionally, color of GPC samples turned gray after elevated temperatures due to dehydration of GPB and microstructural transformations occurring in aggregates. (c) 2021 Elsevier Ltd. All rights reserved.Öğe Influence of various factors on properties of geopolymer paste: A comparative study(Ernst & Sohn, 2020) Kantarci, Fatih; Turkmen, Ibrahim; Ekinci, EnesA comprehensive experimental study was conducted to investigate effect of different production parameters such as activator type, activator concentration and curing temperature on fresh and hardened properties of volcanic tuff based geopolymer paste (GP) samples. Volcanic tuff obtained from Nevsehir (Central Anatolia, Turkey) was ground to particle size less than 45 mu m, after that alkali activation process was provided with two type of alkali activators such as NaOH and NaOH+Na2SiO3(SH and SH + SS) solutions. Produced geopolymer samples were cured at different temperatures ranging from 23 to 150 degrees C. Compressive strength, setting time, hydration heat of GP samples were investigated. Additionally, microstructural investigations were performed with SEM and XRD analyzes. As a result of modification of experimental parameters, compressive strength development reached to 41.43 MPa was obtained from GP samples, which did not harden in laboratory conditions. It was also determined that the alkali activation of volcanic tuff with SH exhibited better mechanical and microstructural properties than alkali activation with SH + SS.Öğe Mechanical and durability characteristics of GGBS-based self-healing geopolymer mortar produced using by an endospore-forming bacterium(Elsevier, 2022) Ekinci, Enes; Turkmen, Ibrahim; Birhanli, EmreHealing process of the gaps and cracks in the structure of geopolymer binders, which have emerged as greener alternatives compared to their traditional Portland cement counterparts, is of great importance in terms of a long economic life. The application of the microbial induced carbonate precipitation (MICP) method, which is the most striking of the various healing techniques applied to building materials, on geopolymer composites has been limited to a few successful studies. At this point, it is considered to be an important step to examine the effects of addition of bacteria on the mechanical and durability characteristics of geopolymer composites in detail. Therefore, this paper was designed to examine the effect of the usage of Bacillus subtilis on the mechanical and durability performance of ground blast furnace slag (GBFS)-based geopolymer mortar (GPM) specimens. In the GPM specimens activated with Na2SiO3, the total liquid/ binder ratio as 0.55 and the binder/fine aggregate ratio as 1:2 was kept constant. Bacterial cultures in liquid form prepared at different concentrations (109 and 107 CFU/mL) were added directly to the Na2SiO3 at 0, 1, 2 and 3% by weight of GBFS. GPM samples, which were prepared in seven different groups in total, were kept in three different curing mediums (precipitation medium, water and ambient conditions) from 7th day to the 28th day. After the curing period was over, the compressive strength, electrical resistivity, sulfate and acid resistance, capillary water absorption, splitting tensile strength and permeability properties were investigated on the GPM samples. In addition, the above-mentioned test results were confirmed by the microstructural analyzes performed. Experimental findings revealed that the optimum bacterial concentration and bacterial dosage values were 107 CFU/mL and 3%, respectively, in terms of both mechanical properties and durability performances. On the other hand, it was observed that all of the GPM specimens cured in precipitation medium (PM) and produced using bacteria had superior performances compared to their counterparts cured in water and ambient conditions. This situation clearly demonstrated that an effective self-healing process that will occur in GPM samples produced with the addition of bacteria directly could only be possible by creating a curing environment containing urea and calcium.Öğe Mechanical properties and setting time of ferrochrome slag based geopolymer paste and mortar(Elsevier Sci Ltd, 2014) Karakoc, Mehmet Burhan; Turkmen, Ibrahim; Maras, Muslum Murat; Kantarci, Fatih; Demirboga, Ramazan; Toprak, M. UgurMany researches have been done to investigate using raw materials in the production of geopolymer cements. This paper presents the effects of alkali dosage and silica modulus when using sodium metasilicate solution at different curing conditions on the geopolymerization of ferrochrome slag (FS). As alkali activation for geopolymerization, NaOH and Na2SiO3 solution were used. Geopolymer cement was produced using FS as raw material with 3 different silica modulus (0.50, 0.60 and 0.70) and 4 different Na2O concentrations (4%, 7%, 10% and 12%). The setting time, hydration heat and compressive strength of geopolymer paste samples and compressive strength of geopolymer mortar samples were obtained. The setting time varied between 120 and 870 min, it showed variability depending on Na2O content. The highest 28 day compressive strength of the geopolymer paste samples was obtained from one with Na2O concentration of 7% and silica modulus of 0.70. Geopolymer mortars were prepared for the determination of compressive strength by adding FS:sand:alkali activator ratio 1:2:0.30, 035 and 0.40. The specimens were cured at 60 degrees C and 80 degrees C kept for 20 h and the other mortar samples were stored under laboratory conditions. Compressive strength of the material decreased, when w/b (water/binder) ratio increased. The highest 28 day strength of the geopolymer mortar was obtained at 0.30 w/b ratio and laboratory temperature curing conditions. The hydration heat of geopolymer paste samples was found to be less than normal Portland cements. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were investigated to study the microstructural properties of the geopolymers. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Mechanical Properties and Setting Time of Geopolymer Paste and Mortar Produced From Ferrochrome Slag(Ieee, 2013) Karakoc, Mehmet Burhan; Turkmen, Ibrahim; Maras, M. Murat; Kantarci, Fatih; Demirboga, Ramazan; Toprak, M. UgurMany researches have been done to investigate using raw materials in the production of geopolymer cements. The aim of this paper is the effect of dosage of alkali and silica modulus when using sodium metasilicate solution at different curing conditions on the geopolymerisation of ferrochrome slag (FS). As alkali activation for geopolymerization, NaOH and Na2SiO3 solution were used. Geopolymer cement was produced using FS and 3 different silica modulus (0.50, 0.60, and 0.70) and 4 different Na2O concentrations (4, 7, 10, and 12%). The setting time, heat of hydration and compressive strength of geopolymer paste samples and compressive strength of geopolymer mortar samples were obtained. The setting time varies between 120 and 870 min, it shows variability depending on content of Na2O. As a result of the highest 28 day strength of the geopolymer paste sample was obtained at Na2O concentration of 7% and at silica modulu of 0.70. Geopolymer mortars were prepared for the determination of compressive strength by adding FS: sand: alkali activator ratio 1:2:0.30, 0.35 and 0.40. The specimens were cured at 60 degrees C, 80 degrees C kept in 20 hours and the other mortars were stored under laboratory conditions. Compressive strength of the material decreases, when w/b ratio increases. The highest 28 day strength of the geopolymer mortar was obtained at 0.30 w/b ratio and at curing temperature laboratory conditions. The hydration heat of geopolymer paste samples was found to be less than normal Portland cements. Microstructural changes in the specimens were studied with SEM and XRD.Öğe Modeling with ANN and effect of pumice aggregate and air entrainment on the freeze-thaw durabilities of HSC(Elsevier Sci Ltd, 2011) Karakoc, Mehmet Burhan; Demirboga, Ramazan; Turkmen, Ibrahim; Can, IbrahimThe objective of this work is to calculate the compressive strength, ultrasound pulse velocity (UPV), relative dynamic modulus of elasticity (RDME) and porosity induced into concrete during freezing and thawing. Freeze-thaw durability of concrete is of great importance to hydraulic structures in cold areas. In this paper, freezing of pore solution in concrete exposed to a freeze-thaw cycle is studied by following the change of concrete some mechanical and physical properties with freezing temperatures. The effects of pumice aggregate (PA) ratios on the high strength concrete (HSC) properties were studied at 28 days. PA replacements of fine aggregate (0-2 mm) were used: 10%, 20%, and 30%. The properties examined included compressive strength, UPV and RDME properties of HSC. Results showed that compressive strength, UPV and RDME of samples were decreased with increase in PA ratios. Test results revealed that HSC was still durable after 100, 200 and 300 cycles of freezing and thawing in accordance with ASTM C666. After 300 cycles, HSC showed a reduction in compressive strength between 6% and 21%, and reduction in RDME up to 16%. For 300 cycles, the porosity was increased up to 12% for HSC with PA. In this paper, feed-forward artificial neural networks (ANNs) techniques are used to model the relative change in compressive strength and relative change in UPV in cyclic thermal loading. Then genetic algorithms are applied in order to determine optimum mix proportions subjected to 300 thermal cycling. (C) 2011 Elsevier Ltd. All rights reserved.Öğe Optimization of production parameters of geopolymer mortar and concrete: A comprehensive experimental study(Elsevier Sci Ltd, 2019) Kantarci, Fatih; Turkmen, Ibrahim; Ekinci, EnesGeopolymers are a new type of material offered as an alternative to traditional Portland cement. Geopolymers, produced by activation of natural and waste pozzolans with alkali activators such as NaOH (SH) and Na2O center dot 3SiO(2) (SS) solutions, have been widely supported and investigated due to environmental and economic advantages. In this study, a detailed experimental program was conducted to investigate the influence of activator type, activator concentration and curing temperature on mechanical and microstructural properties of volcanic tuff based geopolymer mortar (GPM) and concrete (GPC) samples. A total of 1080 GPM and GPC samples were produced and a number of parameters were investigated with 360 combinations. Maximum compressive strength was obtained as 37.09 MPa in 90-day samples in which the SH concentration was 16 M, activator/binder (a/b) ratio was 0.45 and the curing temperature was 120 degrees C. As a result of optimization of the production parameters, a considerable development in mechanical and microstructural properties of GPM and GPC samples was obtained. Experimental results demonstrated that alkali activation with sole SH bring about superior characteristics compared to alkali activation with SH + SS. Higher a/b ratio led to higher UPV values because of more dense and compact microstructure resulting from increase in gopolymerization reactions. This is also supported by compressive strength and microstructure findings. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Performance of self-healing geopolymer paste produced using Bacillus subtilis(Elsevier Sci Ltd, 2022) Ekinci, Enes; Turkmen, Ibrahim; Birhanli, EmreThis study examines the effects of the usage of bacteria as a self-healing agent on the geopolymer paste (GP) sample's characteristics. Examining the microbial self-healing capacity of geopolymer binders, which have many advantages over traditional Portland cement, is seen as an important and necessary step because of frequently studying innovative approaches on geopolymer samples. To carry out this investigation, GP samples produced using ground blast furnace slag (GBFS) were activated only with Na2SiO3. Bacillus subtilis was selected as the healing agent for the production of GP samples. As a result of the preliminary tests in which different variables (curing environment, sample content) were examined, it was decided what the sample content to be used in the main test processes. The bacterial suspensions were prepared at ratios of 107 and 109 CFU/mL. Bacterial samples prepared at two different cell densities were added to the mixture at 1, 2 and 3% by weight of the binder. The GP samples that cured under laboratory conditions until the end of the 7th day, were subjected to healing process in three different curing environments (water, air and precipitation medium consisting of urea, yeast extract and Ca (NO3)2.4H2O After the healing process was completed, the compressive strength, rheological behaviour, geopolymerization kinetics, physical properties, microstructural and visual examinations were performed. Experimental findings demonstrated that the self-healing mechanism resulting from the metabolic activity of Bacillus subtilis can be successfully applied in geopolymer composites in terms of high durability and mechanical properties.Öğe Prediction of compressive strength and ultrasonic pulse velocity of admixtured concrete using tree model M5P(Ernst & Sohn, 2020) Kocamaz, Adnan Fatih; Ayaz, Yasar; Karakoc, Mehmet Burhan; Turkmen, Ibrahim; Demirboga, RamazanThe quality of concrete was assessed based on measurements of ultrasonic pulse velocity (UPV) and compressive strength. Portland cement (PC) was substituted with silica fume (SF), fly ash (FA) and blast furnace slag (BFS) as mineral admixtures. The compressive strength and UPV of concrete mixtures were estimated with classifiers alongside the tree model M5P in the data mining field. The compressive strength and UPV were modeled as a function of five input variables: day, cement, SF, FA, and BFS. It was found that UPV and compressive strength had an exponential correlation with SF, FA, BFS, SF + FA, SF + BFS and FA + BFS. However, additive-free admixture and PC-free substitution levels had a different constant in empirical work. According to the results obtained, both compressive strength and UPV of concrete mixtures could be reliably anticipated with the tree model M5P in a proportion of 97%. Hence, this model could be a potential new method for modeling mineral admixture concrete.Öğe Properties of pumice aggregate concretes at elevated temperatures and comparison with ANN models(Wiley, 2017) Turkmen, Ibrahim; Bingol, A. Ferhat; Tortum, Ahmet; Demirboga, Ramazan; Gul, RuestemThe mechanical properties and thermal conductivity of concretes including pumice aggregate (PA) exposed to elevated temperature were analyzed by thermal conductivity, compressive strength, flexure strength, dynamic elasticity modulus (DEM) and dry unit weight tests. PA concrete specimens were cast by replacing a varying part of the normal aggregate (0-2 mm) with the PA. All concrete samples were prepared and cured at 23 +/- 10C lime saturated water for 28 days. Compressive strength of concretes including PA decreased that reductions were 14, 19, 25 and 34% for 25, 50, 75 and 100% PA, respectively. The maximum thermal conductivity of 1.9382W/mK was observed with the control samples containing normal aggregate. The tests were carried out by subjecting the samples to a temperature of 0, 100, 200, 300, 400 500, 600 and 700 degrees C for 3 h, then cooling by air cooling or in water method. The results indicated that all concretes exposed to a temperature of 500 and 700 degrees C occurred a significant decrease in thermal conductivity, compressive strength, flexure strength and DEM. An artificial neural network (ANN) approach was used to model the thermal and mechanical properties of PA concretes. The predicted values of the ANN were in accordance with the experimental data. The results indicate that the model can predict the concrete properties after elevated temperatures with adequate accuracy. Copyright (C) 2016 John Wiley & Sons, Ltd.Öğe Several properties of mineral admixtured lightweight mortars at elevated temperatures(Wiley, 2013) Turkmen, Ibrahim; Findik, Satuk BugraThe improvement of thermal and mechanical properties of mortars including expanded perlite aggregate (EPA) containing either clinoptilolite, a type of natural zeolite (NZ), waste glass powder (GP) or blast furnace slag (BFS) cured at elevated temperature was analyzed using thermal conductivity, compressive strength, flexure strength and dry unit weight. EPA mortar specimens were prepared by replacing a varying part of the portland cement with the above minerals. All mortar samples were prepared and cured at 23 +/- 1 degrees C lime saturated water for 28 days. The maximum thermal conductivity of 1.3511W/mK was determined with the control samples containing plain cement. GP has shown 1 and 4% decrease for both 10, 20% GP and 25% EPA, respectively. Both BFS and NZ have a decreasing effect on thermal conductivity. The experiments were carried out, in which the samples were subjected to temperature of 300, 500 and 800 degrees C for 2h, then cooled in air. The results indicated that all the mortars exposed to temperature of 500 and 800 degrees C shown a significant decrease in thermal conductivity, compressive strength and flexure strength. However, compared with the mortars including 25% EPA, adding the other admixtures at all level replacement decreased thermal conductivity, compressive strength, flexure strength and dry unit weight as a function of replacement percent. Copyright (c) 2010 John Wiley & Sons, Ltd.Öğe A study of chemical composition and radiation attenuation properties in clinoptilolite-rich natural zeolite from Turkey(Pergamon-Elsevier Science Ltd, 2010) Kurudirek, Murat; Ozdemir, Yueksel; Turkmen, Ibrahim; Levet, AytacClinoptilolite, a type of natural zeolite, has been commonly used as pozzolanic additive in concrete. This type of natural zeolite is generally used as a mineral admixture by substitution in Portland cement to produce high performance concretes. In the present study, the major, minor and trace element levels present in the clinoptilolite-rich natural zeolite (CRNZ) have been determined using a wavelength dispersive X-ray fluorescence spectrometer. Also, the clinoptilolite-rich natural zeolite has been compared with Portland cement with respect to the radiation attenuation properties. From the results it can be concluded that due to the natural radioactive content of clinoptilolite-rich natural zeolite (CRNZ) even if it is in trace level and also due to the poorer X-ray attenuation compared with Portland cement, special care should be taken to use this type of natural zeolite as blend materials in cements, etc. (C) 2010 Elsevier Ltd. All rights reserved.Öğe Sulfate resistance of ferrochrome slag based geopolymer concrete(Elsevier Sci Ltd, 2016) Karakoc, Mehmet Burhan; Turkmen, Ibrahim; Maras, Muslum Murat; Kantarci, Fatih; Demirboga, RamazanThis paper presents the study of the performance of a new geopolymer binding material exposed to sulfate attack. Geopolymer binding material was obtained by alkaline activating FS with chemical materials (NaOH and Na2SiO3). Geopolymer concrete samples were produced by mixing this binding material with river sand and crushed sand aggregates. Test specimens were immersed in magnesium sulfate solutions (by weight 3%, 5% and 7%) for various periods of time and the durability of geopolymer concrete was investigated. The residual compressive strength (90 and 180 days), change in weight and length of samples, pH variation of solution and visual appearance of these samples were obtained experimentally. It was concluded that compressive strength of both geopolymer and Ordinary Portland Cement (OPC) based concrete samples decreases with increasing in MgSO4 content and exposure duration. After exposed to 7% MgSO4 solution for 180 days, the minimum decrease in compressive strength was seen 25% in geopolymer concrete samples with crushed sand aggregates. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
