Yazar "Gülşan, Mehmet Eren" seçeneğine göre listele

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    Development of fly ash/slag based self-compacting geopolymer concrete using nano-silica and steel fiber
    (ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2019) Gülşan, Mehmet Eren; Alzeebaree, Radhwan; Rasheed, Ayad Ali; Niş, Anıl; Kurtoğlu, Ahmet Emin
    This study investigates the simultaneous effect of nano-silica and steel fiber on the fresh and hardened state performance of self-compacting geopolymer concretes (SCGC). For this purpose, self-compacting geopolymer concretes without and with nano-silica (0, 1% and 2%), and without and with steel fiber (0, 0.5% and 1%) were produced. Hooked-end steel fibers were used with a length of 30 mm and an aspect ratio of 40. Self-compacting geopolymer mixes were produced using 50% fly ash (FA) and 50% ground granulated blast furnace slag (GGBFS) with a constant alkaline activator to binder ratio of 0.5. For the alkaline activator, sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) were utilized with a ratio (Na2SiO3/NaOH) of 2.5. Fresh state experiments were carried out via slump flow, L-Box, and V-funnel tests, while hardened state experiments were conducted using compressive strength, flexural strength, and bonding strength tests to estimate the effects of nano-silica and steel fiber together on the resulting performances of SCGC specimens. Test results were also evaluated statistically in order to clarify the contributions of the important parameters on the resulting performance. Moreover, correlations between the experimental data were studied to investigate the relationships between the fresh and hardened state performances. The results demonstrated that incorporation of nano-silica and steel fiber affected the fresh state properties adversely; however, a combined utilization of them improved bond strength and flexural performance of the SCGC specimens significantly. In addition, the effect of nano-silica was found to be dominant on fresh state properties and compressive strength, while the effect of steel fiber was found to be superior on flexural performance and bonding strength.
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    Effect of nano-silica on the chemical durability and mechanical performance of fly ash based geopolymer concrete
    (ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2018) Çevik, Abdulkadir; Alzeebaree, Radhwan; Humur, Ghassan; Niş, Anıl; Gülşan, Mehmet Eren
    In this study, the effect of nano silica on the short term severe durability performance of fly ash based geopolymer concrete (GPC) specimens was investigated. Four types of GPC were produced with two types of low calcium fly ashes (FAI and FAII) with and without nano silica, and ordinary Portland cement concrete (OPC) concrete was also cast for reference. For the geopolymerization process, the alkaline activator has selected a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) with a ratio (Na2SiO3/ NaOH) of 2.5. Main objectives of the study were to investigate the effect of usability or replaceability of nano silica-based low calcium fly ash based geopolymer concretes instead of OPC concrete in structural applications and make a contribution to standardization process of the fly ash based geopolymer concrete. To achieve the goals, four types of geopolymer and OPC concretes were subjected to sulfuric acid (H2SO4), magnesium sulfate (MgSO4) and seawater (NaCl) solutions with concentrations of 5%, 5%, and 3.5%, respectively. Visual appearances and weight changes of the concretes under chemical environments were utilized for durability aspects. Compressive, splitting tensile and flexural strength tests were also performed on specimens to evaluate the mechanical performance under chemical environments. Results indicated that FAGPC concretes showed superior performance than OPC concrete under chemical attacks due to low calcium content. Amongst the chemical environments, sulfuric acid (H2SO4) was found to be the most dangerous environment for all concrete types. In addition, nano silica (NS) addition to FAGPC specimens improved both durability and residual mechanical strength due to the lower porosity and more dense structure. The FAIIGPC specimens including nano silica showed the superior mechanical performance under chemical environment.
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    The Effects of Recycled Tire Rubbers and Steel Fibers on the Performance of Self-compacting Alkali Activated Concrete
    (BUDAPEST UNIV TECHNOLOGY ECONOMICS, PERIODICA POLYTECHNICA, BUDAPEST 1521, HUNGARY, 2021) Eren, Necip Altay; Alzeebaree, Radhwan; Çevik, Abdulkadir; Niş, Anıl; Mohammedameen, Alaa; Gülşan, Mehmet Eren
    In this study, the effects of recycled tire rubbers (RTR) and steel fiber (SF) on the fresh and hardened state properties of the self-compacted alkali activated concrete (SCAAC) were investigated. The ground granulated blast furnace slag, 1 % hooked-end SF, and two types of RTR were utilized. The crumb rubbers (CR) and tire rubber chips (TCR) were used as a substation to natural aggregates at substation levels of 10 % and 15 %. The fresh state performances were evaluated by T50 value, slump flow, V-funnel, and L-Box tests, while mechanical performances were assessed through compressive, flexural, and splitting tensile strength tests. Also, detailed crack and microstructural analyses were conducted. The RTR adversely affected the fresh state properties, which reduced more with SF inclusions. Among the RTR, the TR specimens exhibited lower fresh state performance than the CR specimens. Similar mechanical strengths were obtained on the TR and CR specimens under the same replacement ratios. However, TR specimens exhibited higher deformation capacities than the CR specimens, when SF was utilized. The SCAAC specimens with 1 % SF and 15 % RTR showed more and wider flexural cracks, higher mechanical strength, and deformation capacity, which can be utilized in structural applications, particularly in high seismic zones.
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    Effects of sulphuric acid on mechanical and durability properties of ECC confined by FRP fabrics
    (TECHNO-PRESS, PO BOX 33, YUSEONG, DAEJEON 305-600, SOUTH KOREA, 2018) Gülşan, Mehmet Eren; Mohammedameen, Alaa; Şahmaran, Mustafa; Niş, Anıl; Alzeebaree, Radhwan; Çevik, Abdulkadir
    In this study, the effects of sulphuric acid on the mechanical performance and the durability of Engineered Cementitious Composites (ECC) specimens were investigated. The carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP) fabrics were used to evaluate the performances of the confined and unconfined ECC specimens under static and cyclic loading in the acidic environment. In addition, the use of CFRP and BFRP fabrics as a rehabilitation technique was also studied for the specimens exposed to the sulphuric acid environment. The polyvinyl alcohol (PVA) fiber with a fraction of 2% was used in the research. Two different PVA-ECC concretes were produced using low lime fly ash (LCFA) and high lime fly ash (HCFA) with the fly ash-to-OPC ratio of 1.2. Unwrapped PVA-ECC specimens were also produced as a reference concrete and all concrete specimens were continuously immersed in 5% sulphuric acid solution (H2SO4). The mechanical performance and the durability of specimens were evaluated by means of the visual inspection, weight change, static and cyclic loading, and failure mode. In addition, microscopic changes of the PVA-ECC specimens due to sulphuric acid attack were also assessed using scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that PVA-ECC specimens produced with low lime fly ash (LCFA) showed superior performance than the specimens produced with high lime fly ash (HCFA) in the acidic environment. In addition, confinement of ECC specimens with BFRP and CFRP fabrics significantly improved compressive strength, ductility, and durability of the specimens. PVA-ECC specimens wrapped with carbon FRP fabric showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabric. Both FRP materials can be used as a rehabilitation material in the acidic environment.
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    Mechanical and durability performance of FRP confined and unconfined strain hardening cementitious composites exposed to sulfate attack
    (ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2019) Mohammedameen, Alaa; Gülşan, Mehmet Eren; Alzeebaree, Radhwan; Çevik, Abdulkadir; Niş, Anıl
    In this study, the performance of Fiber Reinforced Polymer (FRP) confined and unconfined Strain Hardening Cementitious Composite (SHCC) specimens exposed to sulfate attack under static and cyclic loading were investigated. Two types of FRP fabrics (Basalt (BFRP) and Carbon (CFRP)) and two types of fly ash (Low calcium (LCFA) and high calcium (HCFA)) were studied. In addition, FRP fabrics as a rehabilitation material was also investigated for the sulfate deteriorated specimens. LCFA-SHCC specimens showed superior performance than HCFA-SHCC specimens in the sulfate environment. In addition, confined specimens with FRP fabrics significantly improved compressive strength, ductility, and durability of the specimens.
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    Performance of FRP confined and unconfined geopolymer concrete exposed to sulfate attacks
    (TECHNO-PRESSPO BOX 33, YUSEONG, DAEJEON 305-600, SOUTH KOREA, 2018) Alzeebaree, Radhwan; Gülşan, Mehmet Eren; Niş, Anıl; Mohammedameen, Alaa; Çevik, Abdulkadir
    In this study, the effects of magnesium sulfate on the mechanical performance and the durability of confined and unconfined geopolymer concrete (GPC) specimens were investigated. The carbon and basalt fiber reinforced polymer (FRP) fabrics with 1-layer and 3-layers were used to evaluate the performances of the specimens under static and cyclic loading in the ambient and magnesium sulfate environments. In addition, the use of FRP materials as a rehabilitation technique was also studied. For the geopolymerization process of GPC specimens, the alkaline activator has selected a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) with a ratio (Na2SiO3/NaOH) of 2.5. In addition to GPC specimens, an ordinary concrete (NC) specimens were also produced as a reference specimens and some of the GPC and NC specimens were immersed in 5% magnesium sulfate solutions. The mechanical performance and the durability of the specimens were evaluated by visual appearance, weight change, static and cyclic loading, and failure modes of the specimens under magnesium sulfate and ambient environments. In addition, the microscopic changes of the specimens due to sulfate attack were also assessed by scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that geopolymer specimens produced with nano-silica and fly ash showed superior performance than the NC specimens in the sulfate environment. In addition, confined specimens with FRP fabrics significantly improved the compressive strength, ductility and durability resistance of the specimens and the improvement was found higher with the increased number of FRP layers. Specimens wrapped with carbon FRP fabrics showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabrics. Both FRP materials can be used as a rehabilitation material in the sulfate environment.