İnşaat Mühendisliği
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Browsing İnşaat Mühendisliği by Subject "Aggregates (Building materials)."
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Item Effects of lightweight fly ash aggregate properties on the performance of lightweight concretes(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2008., 2008.) Koçkal, Niyazi Uğur.; Özturan, Turan.Only a very small content of ash is being used for the construction applications. As large quantities of the fly ash remain unutilized in most countries of the world, the manufacture of light-weight fly ash aggregates is an appropriate step to utilize a large quantity of fly ash. Structural lightweight concrete mixtures can be designed to obtain similar mechanical and durability performance as normalweight concrete. The study is divided into two parts. In the first part of the study, the characteristics of different lightweight fly ash aggregates were investigated. Specific gravity, water absorption, porosity, thermal behaviour, crushing strength and microstructural changes of these aggregates were determined. The properties and microstructure of aggregates were modified by different sintering agents and heat treatments. The strength and specific gravity of all aggregates decreased with increasing the binder content (disregarding binder type) at high temperature. Aggregates with low water absorption and high strength can be attributed to the discontinuous porosity, dense structure and small pore size. In the second part of the study, the influence of properties of lightweight aggregate types on the behaviour of concrete mixtures were discussed. The compressive strength, modulus of elasticity, splitting tensile strength tests, water impermeability test, rapid chloride permeability test, accelerated corrosion studies and rapid freeze/thaw cycling test were performed on lightweight and normalweight concretes. The results of this study revealed the possibility of manufacturing high-strength air-entrained lightweight aggregate concretes using sintered and cold-bonded fly ash aggregates. The use of lightweight aggregates instead of normalweight aggregates in concrete production decreased the strength as expected but improved the resistance to permeability and freeze-thaw of the concretes.Item Investigation of fatigue and durability properties of concrete containing recycled concrete aggregate(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2018., 2018.) Pehlivan, Ahmet Onur.; Özturan, Turan.Population growth and construction industry have grown beyond limits in recent decades which lead to depletion of natural resources with increasing pace. Since this resembles a serious conflict with the desired sustainability and environmental perspec tive, serious efforts are being made to use recycled aggregates in structural concrete rather than dumping in landfills. In this study, four different replacement levels (0, 50, 75, 100%), two w/c ratios were used. Also mixes containing recycled aggregates were slurry treated with slag when mixing concrete. Also, a more sophisticated method called biodeposition was applied on recycled aggregate specimens and SEM analysis were conducted prior to compressive strength tests on mixes containing bacteria treated specimens. Fatigue strength tests under uniaxial compressive loading with two differ ent Smax values (0.85 and 0.75) were applied on specimens to monitor the effects of recycled aggregates on fatigue behavior of concrete. Incorporation of recycled aggre gates into concrete adversely affected the mechanical properties. Slurry treatment were found to be effective on both mechanical performance and durability. Biodeposition treatment was found to be effective in decreasing the water absorption of recycled ag gregates. Fatigue performance of concrete containing recycled aggregates was found to be lower than natural concrete. Number of cycles to failure was more limited for recy cled aggregate specimens and these specimens were not able to withstand higher strain development and failed after a less loss of stiffness with respect to natural concrete specimens and also slurry treated specimens.Item Mechanical and francture properties of pumice lightweight aggregate steel fiber reinforced concrete(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Epözdemir, Ali Can.; Özturan, Turan.Composite materials are widely used with many purposes in contemporary engineering applications. Lightweight composites are mostly used in aerospace and military engineering applications but as well as in construction industry. Reducing the dead loads of the structures has numerous advantages. For this purpose there are several different lightweight aggregates used in the literature. In the context of the current study pumice type of lightweight aggregates used with normal weight aggregates. Steel fibers with different aspect ratios (55, 57 and 65) having the length 30mm, 36mm and 60mm respectively used with two different volume fractions of 0.5% and 1%.Fresh state properties as well as hardened state properties are investigated. Several mechanical properties such as compressive strength, indirect tensile strength, modulus of elasticity etc. are presented. Three different type of fracture tests conducted; namely 3 point bending test with notched specimens, Barcelona test and Generalized Barcelona test. Effect of fiber addition, fiber volume fraction and aspect ratio are investigated evaluating toughness of specimens. Considering Barcelona tests both total circumferential opening displacement (TCOD) and axial displacements used to evaluate the ductile behavior of concrete. Finally, it was observed that increase in fiber volume fraction and aspect ratio significantly improves mechanical and fracture properties of pumice lightweight aggregate concrete.Item Mechanical properties and fracture parameters of sustainable concrete produced with recycled aggregates(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Yıldırım, Hasan.; Zihnioğlu, Nilüfer Özyurt.; Özturan, Turan.In this study, the mechanical properties and fracture parameters of sustainable concrete mixtures produced with different recycled aggregates at a w/c of 0.50 were investigated. To produce sustainable concrete mixtures, recycled concrete aggregates (RCA), recycled brick aggregates (RBA), and recycled fly ash aggregates (FAA) were used in total replacement, by volume, of natural crushed stone coarse aggregates (CSt). The recycled aggregates were utilized in six different sustainable concrete mixtures as plain (RCA, RBA, FAA) and surface treated (TRCA, TRBA, TFAA) by employing ground granulated blast furnace slag (GGBFS) slurry during concrete production as a multi-step concrete mixing method. Microstructural investigations were also carried out on samples taken from recycled aggregates and hardened concrete specimens to examine the effect of recycled aggregate treatment during the concrete mixing procedure with slag slurry on the mechanical properties and fracture parameters of the recycled aggregate concrete. The results of the experiments conducted in this study revealed that complete replacement of the crushed stone coarse aggregate with recycled aggregates reduced the unit weight of fresh concrete by up to 17%, while the compressive strength values were in line with the limitations for structural use. Besides, the treatment of recycled aggregates with GGBFS slurry improved the mechanical properties and fracture parameters of recycled aggregate concrete mixtures with increased statistical reliability. For example, treating recycled aggregates with slag slurry not only increased the bond strength between the reinforcement bars and the concrete mixtures, but also decreased the minimum required anchorage length for the reinforcement to carry the load. The findings of the microstructural investigations confirmed the formation of secondary hydration products as a result of the pozzolanic activity of fine slag grains, which penetrated and filled the voids and cracks on the surface of the treated recycled aggregates and in the interfaces between these aggregates and the concrete matrix, improving the mechanical properties and fracture parameters of the recycled concrete mixtures.