"Improvement of Mechanical Properties of Reinforcing Steel Used in the Reinforced Concrete Structures"

SAEIOIO structural carbon steel, which has a low cost price and wide range of use in the construction industry, has been studied as dual phase (DP) steel subjected to appropriate heat treatment, and its mechanical properties have been investigated under various tempering conditions. Intercritical annealing heat treatment has been applied to the reinforcing steel in order to obtain DP steels with different martensite volume fraction. In addition, these DP steels have been tempered at 200, 300 and 400 'C for 45 min and then cooled to the room temperature. Mechanical properties such as tensile strength, yield strength, reduction in cross-sectional area, total elongation, resilience modulus and toughness have been examined. Furthermore, fractographic examination has been done with scanning electron microscope (SEM) as well as metallographic examination of the steels. As a result of this study, it is found that mechanical properties of DP steel have changed according to the hardness and ratio of martensite phase. In addition, tensile strength, yield strength and resilience modulus of the steels have been reduced. In contrast, the total elongation, reduction of the cross-sectional area and toughness have been increased

Synthesis and characterization of highly efficient CdSe/CdS core/shell nanocrystals with silar technique

Ankara : The Materials Science and Nanotechnology Program of the Graduate School of Engineering and Science of Bilkent University, 2012.Thesis (Master's) -- Bilkent University, 2012.Includes bibliographical references leaves 67-75.Owing to their size tunable electronic structure and optical properties, semiconductor nanocrystal quantum dots (NQDs) have become attractive for a wide range of device applications ranging from life sciences to electronics in the last two decades. However, highly efficient and stable NQDs are essential to reaching high performance with these devices utilizing NQDs. In this thesis, to meet these requirements, a new class of CdSe/CdS core/shell NQDs are studied including their colloidal synthesis and nanocharacterization. In this work, CdSe/CdS core/shell NQDs were synthesized with successive ion layer adsorption and reaction (SILAR) technique, which enabled highly precise shell thickness control and uniform coating of the shell material. When compared to the most commonly used CdSe/ZnS core/shell NQDs, CdSe/CdS core/shell NQDs were found to provide important advantages. First, the lattice mismatch within CdSe and CdS (3.9%) is lower than that within CdSe and ZnS (12%), which was very critical for obtaining highly efficient NQDs. Second, as a result of having lower bandgap in CdS, great enhancement in absorption cross section was achieved with more red-shifted emission, which is not possible with CdSe/ZnS core/shell NQDs. Moreover, suppression of Auger recombination was successfully observed with the partial separation of electron and hole wavefunctions in the synthesized CdSe/CdS core/shell NQDs. With all these attractive properties that were experimentally measured, CdSe/CdS core/shell NQDs were found to make better alternatives to CdSe/ZnS core/shell for numerous applications.Keleştemur, YusufM.S

Bond Performance of the Rubber particles in the Self-Compacting Concrete

Generating more ductile concrete elements by using waste tire rubbers have been studied for thirty years. Researchers have been produced a lot of rubberized concrete from low strength structure applications to self-compacting concretes having high strength and durability. It is possible to have more flexible concrete while using the fiber shaped waste tire rubbers. Critical problem of use of these rubbers is poor adherence between rubbers and cement paste interface. It is assumed that use of pozzolans with the Portland cement will fix this adherence problem. Therefore, waste tire rubbers have been studied in the self-compacting concrete in order to enhance the problem. Portland cement, grand granulated furnace slag and pozzolanic cement were used together for preparing the self-compacting concretes. Bonding performances of waste tire rubbers and reinforced bars in the self-compacting rubberized concrete were investigated experimentally in this study

Improvement of Mechanical Properties of Reinforcing Steel Used in the Reinforced Concrete Structures

SAEIOIO structural carbon steel, which has a low cost price and wide range of use in the construction industry, has been studied as dual phase (DP) steel subjected to appropriate heat treatment, and its mechanical properties have been investigated under various tempering conditions. Intercritical annealing heat treatment has been applied to the reinforcing steel in order to obtain DP steels with different martensite volume fraction. In addition, these DP steels have been tempered at 200, 300 and 400 'C for 45 min and then cooled to the room temperature. Mechanical properties such as tensile strength, yield strength, reduction in cross-sectional area, total elongation, resilience modulus and toughness have been examined. Furthermore, fractographic examination has been done with scanning electron microscope (SEM) as well as metallographic examination of the steels. As a result of this study, it is found that mechanical properties of DP steel have changed according to the hardness and ratio of martensite phase. In addition, tensile strength, yield strength and resilience modulus of the steels have been reduced. In contrast, the total elongation, reduction of the cross-sectional area and toughness have been increased

Utilization of Waste Vehicle Tires in Concrete and Its Effect on the Corrosion Behavior of Reinforcing Steels

The mechanical and physical properties of concrete specimens obtained from replacing natural coarse aggregate with waste vehicle rubber tires at levels of 2vol%, 5vol%, 7vol%, and 10vol% were studied, and the corrosion behavior of reinforcing steels was investigated in these specimens. Corrosion rates were determined by measuring the galvanic current between steel-reinforced concrete specimens both with and without chloride addition. The change in electrode potential of reinforcing steels in these concrete specimens was measured daily for a period of 60 d in accordance with the testing method in ASTM C876. The results show that the use of waste vehicle tires in concrete instead of coarse aggregate decreases the mechanical strength of the specimens, and increases the corrosion rates of the reinforcing steels embedded in the concretes

Bond performance of rubber particles in the self-compacting concrete

Generating more ductile concrete elements by using waste tire rubbers have been studied for thirty years. Researchers have been produced a lot of rubberized concrete from low strength structure applications to self-compacting concretes having high strength and durability. It is possible to have more flexible concrete while using the fiber shaped waste tire rubbers. Critical problem of use of these rubbers is poor adherence between rubbers and cement paste interface. It is assumed that use of pozzolans with the Portland cement will fix this adherence problem. Therefore, waste tire rubbers have been studied in the self-compacting concrete in order to enhance the problem. Portland cement, grand granulated furnace slag and pozzolanic cement were used together for preparing the self-compacting concretes. Bonding performances of waste tire rubbers and reinforced bars in the self-compacting rubberized concrete were investigated experimentally in this study

Corrosion Behavior of Reinforcing Steel Embedded in Concrete Produced with Finely Ground Pumice and Silica Fume

In this study, the mechanical and physical properties of concrete specimens obtained by substituting cement with finely ground pumice (FGP) at proportions of 5%, 10%, 15% and 20% by weight has been investigated, in addition to analyzing the corrosion behavior of reinforcing steels embedded in these specimens. Besides, with the purpose of determining the effect of silica fume (SF) additive over the corrosion of reinforcing steels embedded in concrete with FGP, SF has been entrained to all series with the exception of the control specimen, such that it would replace with cement 10% by weight. Corrosion experiments were conducted in two stages. In the first stage, the corrosion potential of reinforcing steels embedded in the concrete specimens was measured every day for a period of 160 days based on the ASTM C 876 standard. In the second stage, the anodic and cathodic polarization values of the steels were obtained and subsequently the corrosion currents were determined with the aid of cathodic polarization curves. In the study, it was observed that a decrease in the mechanical strength of the specimens and an increase in the corrosion rate of the reinforcing steel had taken place as a result of the FGP addition. However, it was determined that with the addition of SF into concretes supplemented with FGP, the corrosion rate of the reinforcing steel has significantly decreased

DUAL-FAZ ISIL İŞLEMİ UYGULANMIŞ BETONARME ÇELİĞİNİN ÇEKME EĞRİSİNE TEMPERLEME ISIL İŞLEMİNİN ETKİSİ

Bu çalışmasında, inşaat sektörünün temel yapı malzemesi olan ve yurdumuzda bol miktarda üretilen düşük karbonlu SAE1010 inşaat çeliğinden dual-faz çeliği üretilerek, elde edilen bu çeliğin kuvvetuzama eğrisi üzerine temperleme ısıl işleminin etkisi incelenmiştir. İnşaat çeliğine, (α+γ) bölgesinde 20, 40 ve 60 dk süre ile ostenitleme yapıldıktan sonra buz+su karışımında su verilerek farklı martenzit hacim oranlarına sahip dual-faz çelikleri elde edilmiştir. Daha sonra bu dual-faz çelikleri 200, 300 ve 400 oC sıcaklıklarda 45 dk süre ile temperlenerek sakin havada soğutulmuştur. Elde edilen dual-faz çeliklerinin metalografik incelemeleri tamamlandıktan sonra, çekme deneyine tabi tutularak kuvvet-uzama eğrileri elde edilmiştir. Elde edilen bu eğriler yardımıyla numunelerin çekme dayanımı, akma dayanımı ve tokluk gibi mekanik özellikleri belirlenmiştir. Temperleme ısıl işlemi ile birlikte bu çeliklerin çekme ve akma dayanımı değerlerinin düştüğü, tokluk değerlerinin ise arttığı tespit edilmiştir

İnce Daneli Malzeme Kalınlığının, Dane Çapının ve Şev Eğiminin Taşıma Gücüne Etkisi

Bu çalışmada; Elazığ yöresinden alınan ince daneli malzeme kalınlığının, dane çapının ve şev eğiminin taşıma gücüne etkisi araştırılmıştır. Hazırlanmış deney düzeneğinin alt kısmına sırasıyla; 5, 10, 15 ve 20 cm kalınlıklarında ince daneli malzeme tabakalar halinde sıkıştırılarak serilmiştir. Bu malzeme üzerine de; 4.76, 9.53, 19.5, 25.40 ve 40.00 mm çaplarındaki dolgu malzemeleri; 1/4, 1/3.5, 1/3, 1/2.5 ve 1/2 şev eğimlerinde serilerek dolgular hazırlanmıştır. Hazırlanan dolgularda kayma ve çatlama oluşuncaya kadar düşey yönde yüklemeye devam edilmiştir. Aynı dolgular optimum su muhtevasında hazırlanarak taşıma gücünün değişimi incelenmiştir. Yapılan deneyler neticesinde; ince daneli tabaka kalınlığının arttırılması ile taşıma gücünün azaldığı, dolgu malzeme çapının ve şev eğiminin arttırılması ile de taşıma gücünün arttığı görülmüştür. Ayrıca, optimum su muhtevasında hazırlanmış dolgularda, taşıma gücünün çok büyük oranlarda azaldığı yapılan deneylerle tespit edilmiştir. Bulunan deney sonuçlarına bağlı olarak, dolgu taşıma gücünün; ince daneli malzeme kalınlığı, dolgu malzeme çapı ve şev eğimleri ile değişimleri grafiklerle gösterilmiştir

Exciton Dynamics of Colloidal Semiconductor Quantum Well Stacks

Colloidal semiconductor nanoplatelets (NPLs) have recently emerged as a new class of colloidal nanocrystals. NPLs are quasi two-dimensional nanocrystals having atomically flat surfaces and have unique properties such as narrow photoluminescence (PL) emission (similar to 10 nm) and giant oscillator strength. NPLs can be self-assembled into stacks. These are one-dimensional superstructures that can contain tens or hundreds of NPLs in one chain