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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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    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.