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    Adverse effects of high temperatures and freeze-thaw cycles on properties of HFRHSCs containing silica fume and metakaolin
    (Elsevier Ltd, 2018) Çiflikli M.; Sarıdemir M.; Soysat F.
    Adverse effects of high temperatures (HTs) and freeze-thaw (F-T) cycles on the properties of hybrid fibers reinforced high strength concretes (HFRHSCs) containing silica fume (SF) and silica fume + metakaolin (SF + MK) were investigated in this study. Concrete mixtures without and with hybrid fibers (HFs) up to 20% replacement by the weight of Portland cement (PC) with SF and SF + MK were made with the water-binder ratio of 0.25. Experimental studies were conducted on the specimens prepared from these mixtures to determine the ultrasound pulse velocity (Upv), compressive strength (fc), flexural strength (fct,fl) and splitting tensile strength (fct,sp) values of concretes without and with HFs exposed to ambient temperature (AT) and HTs. Moreover, the experimental studies were performed to determine the Upv and fc values of concretes exposed to F-T cycles. Microstructure analyses were also conducted on the specimens to examine the changes in the matrix, interface zone and aggregate of concretes without HFs exposed to AT, HTs and F-T cycles. Experimental results have revealed that replacement ratios of SF and SF + MK have important effects on the properties of concretes without and with HFs. The experimental results have also shown that the fc, fct,fl and fct,sp values of the concretes with HFs are higher than the concretes without HFs. The Upv, fc, fct,fl and fct,sp values of the concretes with HFs have been affected more than that of the concretes without HFs due to the adverse effects of HTs. © 2018 Elsevier Ltd
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    Mechanical and microstructural properties of HFRHSCs containing metakaolin subjected to elevated temperatures and freezing-thawing cycles
    (Elsevier Ltd, 2018) Sarıdemir M.; Çiflikli M.; Soysat F.
    Mechanical and microstructural properties of hybrid fibers reinforced high strength concretes (HFRHSCs) containing metakaolin (MK) and metakaolin + silica fume (MK + SF) subjected to elevated temperatures and freezing-thawing (F-T) cycles were investigated in this paper. In the concrete mixtures without and with hybrid fibers, MK and MK + SF were replaced with eight percentage of cement by weight. A total of sixteen concrete mixtures were produced at a water-to-binder ratio of 0.25. Ultrasound pulse velocity (U pv ), compressive strength (f c ), splitting tensile strength (f sts ) and flexural strength (f fs ) tests were performed to evaluate the properties of HFRHSCs subjected to ambient and elevated temperatures (300, 400 and 500 °C). The U pv and f c tests of HFRHSCs subjected to F-T cycles were also conducted. Moreover, the alterations in the matrix, interface zone and aggregate of concretes without hybrid fibers subjected to ambient temperature, elevated temperatures and F-T cycles were analyzed by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) spot and polarized light microscope (PLM). The results of tests have shown that the replacement levels of MK and MK + SF have important influences on the mechanical and microstructural properties of high strength concretes. Moreover, the mechanical results have shown that the concretes with hybrid fibers have higher f c , f sts and f fs than other concretes. The results have also shown that the U pv , f c , f sts and f fs values of concretes without and with hybrid fibers decrease, as the temperature increases. © 2017