Mechanical, durability and microstructure properties of concrete containing natural zeolite

Memduh Nas,Şirin Kurbetci 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.5

Concrete is one of the most widely used construction materials in the world. Producing economical and durable concrete is possible by employing pozzolanic materials. The aim of this study is to underline the possibility of the utilization of natural zeolite in producing concrete and investigate its effects basically on the strength and durability of concrete. In the production of concrete mixes, Portland cement was replaced by the natural zeolite at ratios of 0%, 10%, 15%, and 20% by weight. Concretes were produced with total binder contents of 300 kg/m3 and 400 kg/m3, but with a constant water to cement ratio of 0.60. In addition to compressive and flexural strength measurements, freeze-thaw and high temperature resistance measurements, rapid chloride permeability, and capillary water absorption tests were performed on the concrete mixes. Compared to the rest mixes, concrete mixes containing 10% zeolite yielded in with the highest compressive and flexural strengths. The rapid chloride permeability and the capillary measurements were decreased as the natural zeolite replacement was increased. Freeze-thaw resistance also improved significantly as the replacement ratio of zeolite was increased. Under the effect of elevated temperature, natural zeolite incorporated concretes with lower binder content yielded higher compressive strength. However, the compressive strengths of concretes with higher binder content after elevated temperature effect were found to be lower than the reference concrete.

Low-cycle fatigue in steel H-piles of integral bridges; a comparative study of experimental testing and finite element simulation

Memduh Karalar,Murat Dicleli 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.1

Integral abutment bridges (IABs) are those bridges without expansion joints. A single row of steel H-piles (SHPs) is commonly used at the thin and stub abutments of IABs to form a flexible support system at the bridge ends to accommodate thermal-induced displacement of the bridge. Consequently, as the IAB expands and contracts due to temperature variations, the SHPs supporting the abutments are subjected to cyclic lateral (longitudinal) displacements, which may eventually lead to low-cycle fatigue (LCF) failure of the piles. In this paper, the potential of using finite element (FE) modeling techniques to estimate the LCF life of SHPs commonly used in IABs is investigated. For this purpose, first, experimental tests are conducted on several SHP specimens to determine their LCF life under thermal-induced cyclic flexural strains. In the experimental tests, the specimens are subjected to longitudinal displacements (or flexural strain cycles) with various amplitudes in the absence and presence of a typical axial load. Next, nonlinear FE models of the tested SHP specimens are developed using the computer program ANSYS to investigate the possibility of using such numerical models to predict the LCF life of SHPs commonly used in IABs. The comparison of FE analysis results with the experimental test results revealed that the FE analysis results are in close agreement with the experimental test results. Thus, FE modeling techniques similar to that used in this research study may be used to predict the LCF life of SHP commonly used in IABs.

Durability properties of concrete containing metakaolin

Nas, Memduh,Kurbetci, Sirin Techno-Press 2018 Advances in concrete construction Vol.6 No.2

The main aim of this study is to investigate the possible effects of metakaolin on strength and durability properties of concrete. For this purpose, concrete mixtures are produced by substituting cement with metakaolin 0, 5, 10 and 20% by weight. The amount of binder for the concrete mixtures are 300 and $400kg/m^3$ with a constant water to cement ratio of 0.6. Compressive and bending strengths, freeze-thaw and high-temperature resistances, capillary coefficients and rapid chloride permeability properties were determined and compared each other. Because of all the experiments conducted, it has been found that the use of metakaolin as a pozzolanic additive in concrete have positive effects especially on compressive and bending strengths, capillary, rapid chloride permeability, freeze-thaw resistance, and high temperatures, up to $800^{\circ}C$. The results indicated that the performance of concrete can be enhanced by metakaolin. Particularly, compressive strength and durability properties have found to be improved with increasing metakaolin content which is attributed to pozzolanic activity and filler effect. Furthermore, metakaolin has relatively positive impacts under elevated temperatures and freeze-thaw effects. However, almost all the strengths of entire concrete specimens are lost at $800^{\circ}C$. Consequently, the optimum metakaolin substitution ratio can be suggested to be 20% as per this study.

Structural and optical characteristics of antimony selenosulfide thin films prepared by two-step method

Turkoglu Fulya,Ekren Memduh Emirhan,Cantas Ayten,Yakinci Kubra,Gundogan Hazal,Koseoglu Hasan,Aygun Gulnur,Ozyuzer Lutfi 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.3

Antimony triselenide (Sb2Se3) is one of the most promising absorber material choices among the inorganic semiconductors that has attracted much attention today. However, highest recorded efciencies for Sb2Se3 solar cells are still lower than ideal. Exploring antimony selenosulfde (Sb2(SxSe1−x)3) to increase device performance is one option because some features of alloyed Sb2(SxSe1−x)3 depend on composition such as bandgap and band position. In this study, two-step process was used to grow Sb2(SxSe1−x)3 thin flms. In the frst stage, Sb2Se3 thin flms were deposited on soda lime glass substrates using direct current magnetron sputtering technique. In the second stage, Sb2Se3 thin flms were exposed to sulfurization process in a quartz ampoule to obtain Sb2(SxSe1−x)3 thin flms. Characterization results showed that morphological, optical, and structural properties of Sb2(SxSe1−x)3 thin flms grown by presented method were highly dependent on amount of sulfur in the flms. By the adjustment of the S/S+Se atomic ratio, Sb2(SxSe1−x)3 absorber materials with suitable bandgap, favorable orientation and compact morphology can be obtained for photovoltaic applications.

Durability properties of mortars with fly ash containing recycled aggregates

Kurbetci, Sirin,Nas, Memduh,Sahin, Mustafa Techno-Press 2022 Advances in concrete construction Vol.13 No.1

The rapid development of the construction industry in the world causes a rapid increase in the consumption of aggregate resources, which leads to the depletion of existing aggregate reserves. The use of recycled aggregate in the production of concrete and mortar may be a good solution to reduce the use of natural raw materials and to reduce demolition waste in the environment. In this study investigating the use of recycled aggregate in mortar production, mortar mixtures were produced by substituting 0%, 25%, 50% and 100% fine recycled aggregate (FRA) instead of natural aggregate. The effect of 20% and 40% fly ash (FA) substitutes on cement mortar performance was also investigated. Compressive and flexural strength, drying shrinkage, abrasion resistance, water absorption and capillary water absorption were investigated on the produced mortars. The increase in the use of FRA reduced the compressive and flexural strengths of mortars. While the capillarity coefficients, water absorption, rapid chloride permeability and drying shrinkage of the mortars increased with the increase in the use of FRA, the effect of the use of fly ash on the rate of increase remained lower. The increased use of FRA has improved abrasion resistance as well.

Neuroprotective Effects of Quetiapine on Neuronal Apoptosis Following Experimental Transient Focal Cerebral Ischemia in Rats

Yilmaz, Muhammet Bahadir,Tonge, Mehmet,Emmez, Hakan,Kaymaz, Figen,Kaymaz, Memduh The Korean Neurosurgical Society 2013 Journal of Korean neurosurgical society Vol.54 No.1

Objective : This study was undertaken in the belief that the atypical antipsychotic drug quetiapine could prevent apoptosis in the penumbra region following ischemia, taking into account findings that show 5-hydroxytryptamine-2 receptor blockers can prevent apoptosis. Methods : We created 5 groups, each containing 6 animals. Nothing was done on the K-I group used for comparisons with the other groups to make sure adequate ischemia had been achieved. The K-II group was sacrificed on the 1st day after transient focal cerebral ischemia and the K-III group on the 3rd day. The D-I group was administered quetiapine following ischemia and sacrificed on the 1st day while the D-II group was administered quetiapine every day following the ischemia and sacrificed on the 3rd day. The samples were stained with the immunochemical TUNEL method and the number of apoptotic cells were counted. Results : There was a significant difference between the first and third day control groups (K-II/K-III : p=0.004) and this indicates that apoptotic cell death increases with time. This increase was not encountered in the drug groups (D-I/D-II : p=1.00). Statistical analysis of immunohistochemical data revealed that quetiapine decreased the apoptotic cell death that normally increased with time. Conclusion : Quetiapine is already in clinical use and is a safe drug, in contrast to many substances that are used to prevent ischemia and are not normally used clinically. Our results and the literature data indicate that quetiapine could help both as a neuronal protector and to resolve neuropsychiatric problems caused by the ischemia in cerebral ischemia cases.

Effects of general and spinal anesthetic techniques on endothelial adhesion molecules in cesarean section

Mehtap Honca,Tarık Purtuloglu,Emin Ozgur Akgul,Muzaffer Oztosun,Tevfik Honca,Ali Sizlan,Mehmet Agilli,İbrahim Aydin,Memduh Yetim,Fevzi Nuri Aydin,Halil Yaman 대한마취통증의학회 2014 Korean Journal of Anesthesiology Vol.66 No.5

Background: The aim of this study was to investigate the effects of anesthetic techniques used during general anesthesia (GA) and spinal anesthesia (SA) on endothelial adhesion molecules in the fetal circulation of healthy parturients undergoing elective cesarean section. Methods: Patients were randomly assigned to either the general anesthesia (n = 20) or spinal anesthesia (n = 20) group. Maternal and cord blood neopterin, sE-selectin, and sL-selectin levels were measured in both groups. Results: Cord blood neopterin concentrations in the SA group were not different from those in the GA group, but maternal neopterin levels in the SA group were different from those in the GA group. Maternal blood levels of sE-selectin and sL-selectin were not different between the two groups. Similarly, the cord blood levels of sE-selectin and sL-selectin were not different between the two groups. We found an increased inflammatory process in the fetal circulation depending on the anesthetic method used. Conclusions: These results indicate the effects of general and spinal anesthetic techniques on serum sL-selectin, sE-selectin, and neopterin levels in neonates and parturients undergoing elective cesarean section. sE-selectin and neopterin concentrations and leukocyte counts were higher in the fetal circulation than in the maternal circulation during both GA and SA.