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    Effect of recycled asphalt waste on mechanical properties of alkali-activated mortars
    (Sage Publications Ltd, 2023) Dokuzlar, Gizem; Dundar, Behcet; Yurt, Umit
    In the next century, negative effects, such as an increase in temperature level, rise in sea level and decrease in forests and agricultural areas, are expected as a result of the harmful effects of global warming. The construction industry is among the main actors of global warming. Cement, the most used building material of the construction industry, is responsible for approximately 8% of CO2 emissions worldwide. Reducing the amount of cement production and using alternative materials and wastes can contribute to reducing CO2 emissions in the production of building materials. In this study, Alkali-Activated Mortar (AAM) mixtures which contain Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash (FA) were prepared. Recycled Asphalt Waste (RAW) is reduced to 0-4 mm size in order to use as fine aggregate in AAM mixes. Three different activation temperatures (40 degrees C, 80 degrees C and 120 degrees C) were applied for 18 h in order to examine the effect of activation temperature on the prepared AAM samples. After the application of activation temperature, the samples were kept in the standard curing pool for 7 and 28 days. After curing, physical and mechanical experiments were carried out on AAM samples. Water absorption and porosity, compressive strength and electrical resistivity tests were performed on the hardened samples. In addition, the acid effect on the samples was investigated comparatively with the changes in mechanical and physical properties. As a result, the study, in which high-strength mortar mixtures were obtained, shows promising results in terms of sustainable environmentalism. The compressive strength value of 45.74 MPa was found in the mortar mixtures produced using RAW. In addition, it was concluded that the optimum activation temperature is an important parameter of compressive strength and acid resistance.
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    Examination of cryogenic durability in self-consolidating concretes through mechanical and fracture mechanics approaches
    (Elsevier, 2024) Yurt, Umit; Emiroglu, Mehmet
    Thermal shocks under extreme conditions, such as leakage in concrete-enclosed tanks, which are a popular choice for cryogenic liquid storage, may lead to undesirable effects on the structures. In this study, the effects of cyclic cryogenic exposures have been investigated using both mechanical and fracture mechanics approaches. To ensure durable concrete, self-consolidating concretes have been chosen in the mix design. While previous studies have primarily investigated the effects of a single cryogenic exposure on conventional concrete, this study focuses on repetitive exposure to cryogenic effects on self-consolidating concretes. Furthermore, the selfconsolidating concretes were subjected to two different curing conditions: air curing and water curing, before cryogenic processing, in order to consider real application conditions and laboratory circumstances. After the first and fifth cryogenic exposures, fundamental engineering properties and fracture mechanics parameters were evaluated. To determine the fracture mechanics parameters, beams of three different dimensions were produced, with three different notch lengths for each dimension. The dynamic modulus of elasticity, ultrasonic pulse velocity, compressive strength, and bending strength of self-consolidating concretes were examined after 0, 1, and 5 cycles of cryogenic exposure. As a result, the air-cured samples exhibited greater resistance to cryogenic cycles than the water-cured samples. The KIC and CTODC values increased after one cycle of cryogenic exposure, as noted in the literature. However, the results obtained in this study demonstrate a decrease in KIC and CTODC values after five cycles compared to one cycle of cryogenic exposure.
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    An experimental study on fracture energy of alkali activated slag composites incorporated different fibers
    (Elsevier, 2020) Yurt, Umit
    This paper intended to comparatively investigate the fracture behavior of alkali activated slag concrete (AASC) containing glass fiber (GF), basalt fiber (BF) and polypropylene fiber (PP). Sodium hydroxide (8 mol, 10 mol and 12 mol aqueous solutions) and sodium silicate, and three different fiber dosages (1 kg/m(3), 2 kg/m(3) and 3 kg/m(3)) were used in the production of the fiber reinforced alkali activated slag composites (FRAASC). Additionally, a relatively low activation temperature of 60 degrees C as a curing condition to activate the AASC specimens was adopted in terms of ensuring energy-effective production in the study. Three-point bending tests were conducted to determine the fracture energy (Gf) values on notched beam specimens. In the study, the Gf values were measured by calculating the area under the curve of load and crack mouth opening displacement (CMOD) values. In addition, destructive and non-destructive tests such as splitting tensile strength, compressive strength, dynamic modulus of elasticity (DMoE), ultrasonic pulse velocity, density and porosity were applied onto the hardened AASC specimens. Microstructure analysis was carried out by Energy-Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Microscopy (SEM). As a result, usage of GFs, BFs and PPs increases the energy dissipation capacity and ductility of FRAASCs. An increase of 84% for Gf values was observed from the FRAASC specimens having 8 molarity of sodium hydroxide aqueous solutions with polypropylene fibers. Based on the test results, it can be clearly said that using of glass, basalt and polypropylene fiber is improving the ductile behavior of eco-efficient slag based alkali-activated composites.
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    High performance cementless composites from alkali activated GGBFS
    (Elsevier Sci Ltd, 2020) Yurt, Umit
    Some of the thermally activated minerals and pozzolans were generally preferred in the production of geopolymer and/or alkali-activated composites as unary, binary, and ternary mixtures. The general trend is to use Ground Granulated Blast Furnace Slag (GGBFS) as binary or ternary mixes in the production of alkali-activated composites. However, GGBFSs have preferred the only binder in this study. Alkali-Activated Concrete (AAC) specimens were produced by using sodium hydroxide and sodium silicate aqueous solutions in three different molarity values (8, 10, and 12 M) for the formation of activation. For each mixture, three different activation temperatures, 25 degrees C (ambient temperature), 60 degrees C and 90 degrees C for 18 h, were applied. After this process, the specimens were kept under laboratory conditions (25 +/- 2.5 degrees C) for 90 days to gain strength. Then capillary water absorption, density, Dynamic Modulus of Elasticity (DMoE), compressive strength, splitting tensile strength, and abrasion resistance tests were performed on the specimens. Furthermore, microstructure analyses were performed on the selected specimens. In the conclusion, AAC production was able to achieve using 100% GGBFS. High strength cementless concretes with a compressive strength of 82.32 MPa could be obtained by using GGBFS, which is a waste material. Besides, AAC with an abrasion value of 3.86% by weight was obtained in the specimen coded M12T60. (C) 2020 Elsevier Ltd. All rights reserved.