Yazar "Sahmaran, Mustafa" seçeneğine göre listele

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    Assessment of self-sensing capability of Engineered Cementitious Composites within the elastic and plastic ranges of cyclic flexural loading
    (Elsevier Sci Ltd, 2017) Al-Dahawi, Ali; Yildirim, Gurkan; Ozturk, Oguzhan; Sahmaran, Mustafa
    Engineered Cementitious Composites (ECC) are emerging construction materials with proven mechanical and durability characteristics. These outstanding properties make the material an attractive choice for different infrastructure types. But the growing use of ECCs brings about the need to monitor the health of the structures that employ them. This study therefore focused on the self-sensing capability of ECC with different carbon-based materials (multi-walled carbon nanotubes [CNT], graphene nanoplatelets [GNP], carbon black [CB] and carbon fibers [CM when subjected to repetitive loading and unloading cycles within the elastic and plastic ranges. Tests were conducted on beam specimens loaded and unloaded under four-point bending loading. Within the elastic range, 30% of the ultimate flexural strength was decided for application on the tested specimens. For the plastic range, prismatic specimens prepared for cyclic flexural loading at high levels were loaded up to 70% of their ultimate flexural strength. Experimental findings showed that for all proposed ECC mixtures, self-sensing of imposed damage (i.e. loading) was successful for both elastic and plastic ranges, while the self-sensing of load removal (i.e. unloading) in the elastic range was not achieved as successfully. This was most probably due to very small imposed damage and continuously increasing intrinsic electrical resistivity of individual carbon based materials under loading, which cannot be discharged upon unloading. Compared to other carbon-based materials, CF utilization during ECC production was the most effective method for self sensing of cyclic loading and unloading in the elastic and plastic ranges. Improving the proven superior mechanical and durability properties of ECC materials with self-sensing characteristic will multiply the benefits for truly sustainable infrastructures. (C) 2017 Elsevier Ltd. All rights reserved.
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    Deflection-hardening hybrid fiber reinforced concrete: The effect of aggregate content
    (Elsevier Sci Ltd, 2016) Banyhussan, Qais Sahib; Yildirim, Gurkan; Bayraktar, Ender; Demirhan, Serhat; Sahmaran, Mustafa
    High Performance Fiber Reinforced Concretes (HPFRC) are emerging materials with superior mechanical properties accounting for crack occurrence and propagation under excessive tensile loads along with the many commonly encountered durability issues. One drawback of such materials is the restricted size and amount of coarse aggregates used in mixtures incorporating single or hybrid fibers (in most cases). This, therefore, increases the amount of binder resulting in higher cost, dimensional instability and cracking potential (especially at early ages). In this study, HPFRC mixtures with a maximum aggregate size of 12 mm were developed with maximal variation in coarse aggregate contents without compromising deflection-hardening behavior. Three different fibers were used at a maximum of 2% of volume in single or hybrid systems: polyvinyl-alcohol (P), hooked-end steel (S) and nylon (N) fibers. To function synergistically with different fiber types and high amounts of coarse aggregates, matrix properties were optimized by varying the proportions of fly ash to Portland cement (FA/PC ratios of 0.20, 0.45, and 0.70, by weight) and aggregate to binder (A/B ratios of 1.0, 1.5, and 2.0, by weight). Experimental results showed that a deflection-hardening response can be obtained from HPFRC mixtures with single or hybrid fiber systems regardless of the FA/PC ratio, A/B ratio, and initial curing age selected without endangering the compressive and flexural strength results. It is believed that production of hybrid fiber composite mixtures with high concentrations of coarse aggregates and industrial by-products can contribute to superior mechanical and durability performance, enhanced greenness, as well as the widespread usage of such materials in the field at a reasonable price compared to their counterparts. (C) 2016 Elsevier Ltd. All rights reserved.
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    Determination of Self-Healing Performance of Cementitious Composites Under Elevated CO2 Concentration by Resonant Frequency and Crack Opening Measurements
    (Springer International Publishing Ag, 2018) Keskin, Suleyman Bahadir; Ozlem, Kasap Keskin; Yildirim, Gurkan; Sahmaran, Mustafa; Anil, Ozgur
    Global warming is a phenomenon that incontrovertibly affects daily lives of human beings in almost all aspects. Definitely, construction industry, especially concrete as most commonly used construction material, is not exempt from the effects of global warming. Nevertheless, there is a lack of information on how the change in atmospheric conditions influences self-healing behavior of cementitious materials. This research examines the impact of increased CO2 concentrations in the atmosphere on the self-healing capability of cementitious materials in terms of resonant frequency and crack opening measurements. For this purpose, to clearly disclose the effect of tremendous increase in the environmental CO2 concentration as a result of global warming, Engineered Cementitious Composites (ECC) which possess advanced intrinsic self-healing capability were employed. For this purpose, sound and pre-cracked ECC specimens containing fly ash and ground granulated blast furnace slag were tested by resonant frequency after 28 days of initial curing up to 28 + 90 days with 15 days intervals and crack openings were observed for each testing age. Moreover, in order to accelerate the capture of CO2 from the environment, a third ECC mixture was prepared by adding Ca(OH)(2) to the ECC mixture incorporating fly ash. The results showed that CO2 present in the environment can improve the self-healing behavior of ECC mixtures, which is a promising finding in terms of environmental concerns. Possibility of capturing and decreasing the CO2 from the atmosphere by self-healing mechanism will make the ECC a more environmentally friendly construction material additional to its superior technical properties.
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    Electrical percolation threshold of cementitious composites possessing self-sensing functionality incorporating different carbon-based materials
    (Iop Publishing Ltd, 2016) Al-Dahawi, Ali; Sarwary, Mohammad Haroon; Ozturk, Oguzhan; Yildirim, Gurkan; Akin, Arife; Sahmaran, Mustafa; Lachemi, Mohamed
    An experimental study was carried out to understand the electrical percolation thresholds of different carbon-based nano- and micro-scale materials in cementitious composites. Multi-walled carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and carbon black (CB) were selected as the nano-scale materials, while 6 and 12 mm long carbon fibers (CF6 and CF12) were used as the micro-scale carbon-based materials. After determining the percolation thresholds of different electrical conductive materials, mechanical properties and piezoresistive properties of specimens produced with the abovementioned conductive materials at percolation threshold were investigated under uniaxial compressive loading. Results demonstrate that regardless of initial curing age, the percolation thresholds of CNT, GNP, CB and CFs in ECC mortar specimens were around 0.55%, 2.00%, 2.00% and 1.00%, respectively. Including different carbon-based conductive materials did not harm compressive strength results; on the contrary, it improved overall values. All cementitious composites produced with carbon-based materials, with the exception of the control mixtures, exhibited piezoresistive behavior under compression, which is crucial for sensing capability. It is believed that incorporating the sensing attribute into cementitious composites will enhance benefits for sustainable civil infrastructures.
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    Piezoresistive behavior of CF- and CNT-based reinforced concrete beams subjected to static flexural loading: Shear failure investigation
    (Elsevier Sci Ltd, 2018) Yildirim, Gurkan; Sarwary, Mohammad Haroon; Al-Dahawi, Ali; Ozturk, Oguzhan; Anil, Ozgur; Sahmaran, Mustafa
    Self-sensing property of concrete is mostly assessed using small specimens without reinforcement, which may be misleading for real-time structures. To better simulate the actual field conditions, this study examined self-sensing of damage in large-scale reinforced concrete beams tested under four-point bending. During flexural testing, special attention was paid to the self-sensing capability of shear failure, since this type of failure occurs suddenly and catastrophically. Inadequate shear reinforcements were used to increase shear failure possibility of 100 x 150 x 1000 mm(3) (width x height x length) reinforced large-scale beams and beams were produced with a high shear span (a= 350 mm) to effective depth (d = 125 mm) ratio of 2.8. To increase the electrical conductivity of large-scale beams, chopped carbon fibers (CF) and multi-walled carbon nano tubes (CNT) were used. Instantaneous self-sensing recordings were made using brass electrodes embedded in different shear spans of beams. In addition to conducting self-sensing evaluations, researchers also investigated the effects of CF and CNT particles on the mechanical properties/structural behavior of large-scale beam specimens with the proposed reinforcement configuration. Results showed that compared to CNT, CF usage significantly improved the load carrying capacity and ductility, resulting in bending mode of failure even with indaquate shear reinforcement. Shear damage was successfully self-sensed in all tested beams, although all CF-based specimens started self-sensing from the beginning of loading with significantly higher changes in electrical resistivity results, unlike CNT-based specimens. Conductive network of CF-based specimens seemed to be disturbed more easily at high load levels. CF usage seems like a better option compared to CNT given its lower cost and easier mixability. (C) 2018 Elsevier Ltd. All rights reserved.
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    Self-healing performance of aged cementitious composites
    (Elsevier Sci Ltd, 2018) Yildirim, Gurkan; Khiavi, Arash Hamidzadeh; Yesilmen, Seda; Sahmaran, Mustafa
    This study investigates the autogenous self-healing capability of one-year-old engineered cementitious composites (ECC) with different mineral admixtures to understand whether self-healing performance in late ages is similar to that of early ages. Sound and severely pre-cracked specimens were subjected to different environmental conditions including water, air, CO2-water, and CO2-air for one year plus 90 days of initial curing. Self-healing performance of ECC mixtures was assessed in terms of crack characteristics, electrical impedance testing, rapid chloride permeability testing and microstructural analysis. Laboratory findings showed that the presence of water is crucial for enhanced autogenous self-healing effectiveness, regardless of mixture composition. CO2-water curing resulted in the best self-healing performance of all curing conditions, which was confirmed with results from different performance tests throughout the experimental study. By further curing specimens under CO2-water (depending on the ECC mixture composition), cracks as wide as half a millimeter (458 mu m) were easily closed by autogenous self-healing within only 30 days of further curing, and all cracks closed completely after 90 days. Because high levels of CO2 emission are a global problem, the effectiveness of CO2-water curing in closing microcracks of aged cementitious composites specimens through autogenous self-healing can help reduce the increasing pace of CO2 release. The results of this study clearly suggest that late-age autogenous self-healing rates of ECC specimens can be significantly enhanced with proper further environmental conditioning and mixture design. (C) 2018 Elsevier Ltd. All rights reserved.
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    Self-Sensing Behavior Under Monotonic and Cyclic Loadings of ECC Containing Electrically Conductive Carbon-Based Materials
    (Springer International Publishing Ag, 2018) Sahmaran, Mustafa; Al-Dahawi, Ali; Farzaneh, Vadood; Ocal, Oguzhan; Yildirim, Gurkan
    The development of self-sensing (piezoresistivity) feature which is one of the non-structural properties of cementitious composites to be multifunctional is under focus in the present study. This capability is considered as one of the best alternatives to continuously monitor the damage and deformations of infrastructures. The self-sensing behavior of cubic and prismatic specimens under monotonic uniaxial compression and cyclic flexural loadings respectively was investigated and compared with dielectric ECC materials. The results showed that the incorporation of carbon-based electrically conductive materials within the cementitious composites have a significant effect on monitoring the damage and deformation of cement-based materials effectively.