Investigation of Self-Compacting Concrete by Using Fracture Mechanics Methods

Over a century, concrete has been used as a construction material all over the world, andits application areas increases and becomes commonplace each day. SCC is a special concretetype which places itself in densely-equipped narrow and deep sections with its own weight,tightens without any vibrations, has high resistance or durability characteristics andperformances, and has a very fluid- consistency. Fracture Mechanics researches defects that increase stress concentration such as notch, crack and flaws in the material and the damages occurring in relation to these defects. Therefore, a cracked construction could be analyzedonly by using fracture mechanics methods, that is, by determining fracture parameters realistically. Fracture parameters are among the most important characteristics of hardenedconcrete. In this study, SCC was investigated via the two-parameter fracture model whichneeds two fracture parameters namely: the critical stress intensity factor KIcs and the criticalcrack mouth opening displacement CTODc to characterize failure of concrete structures. InSCC mix, silica fume, fly ash and marble powder were used as powder materials. Sincephysical characteristics of the powder materials used are different, fresh concretecharacteristics of the series display differences. Water curing was applied to all the concretespecimens. Although concrete mix ratio and storage conditions of all series are the same,powder admixture type affected concrete compressive strength. It is known that there is aclose relation between concrete compressive strength and fracture parameters. Based onmaximum loads of SCC specimens produced with different powder materials, critical stressintensity factor KIcs and critical crack tip opening displacement CTODc, fracture parameterswere determined. Consequently, it was observed that concrete compressive strength andpowder admixture type are effective on fracture parameters of concrete

Biochemical analysis of aqueous humor in diabetic and non-diabetic patients with cataracts

Background: Although there are many factors stated in the etiology of cataract, the mechanisms which are formed during the formation of cataract are still not illuminated. The purpose of this study is to evaluate the biochemical analysis of aqueous humor in diabetic and non-diabetic patients with cataract in terms of the existence of pseudoexfoliation (PSX). Material and methods: Seventy-six patients who presented to our ophthalmology clinic with the complaint of cataract and who were planned to undergo phacoemulsification and IOL implementation were included in the study. The patients were classified into 4 groups as Group I: Cataracts with diabetes and without PSX, Group II: Cataracts without diabetes and PSX, Group III: Cataracts with diabetes and PSX, Group IV: Cataracts without diabetes and with PSX. The groups were compared statistically in terms of biochemical analysis of aqueous humor. Results: The mean age of the patients was 68.0 ± 8.5, and 51.3% of the patients were male. In Group II, Na value was significantly higher than in Group I and Group III. In Group IV, Na value was significantly higher than in Group I and Group III. Cl value in Group IV was significantly higher than in Group I-III-III. In Group IV, Ca value was significantly higher than in Group I-III-III. In Group I, P value was significantly higher than in Group II and Group III. Glucose levels in Group I were significantly higher than in Group II-III-IV. Glucose levels in Group III were significantly higher than in Group II-IV. Na value in the PSX (+) group was significantly lower than in the PSX (–) group. In the PSX (+) group, glucose value was significantly higher than in the PSX (–) group. Conclusion: High glucose and low Na levels in the anterior chamber may play a role in the development of PSX and PSCC. High P level in the anterior chamber may be contributed to the development of cataract in diabetic non-PSX eyes. In non-diabetic PSX (+) group, high Ca and Cl levels may be contributed to developing cataracts

Fresh and hardened properties of steel fiber reinforced concrete produced with fibers of different lengths and diameters

Concrete is a brittle material which has a low tensile strength and a low tensile strain capacity. These weak points of concrete can be resolved by including fibers made of different materials with high technical specifications. This special type of concrete is known as Steel Fiber Reinforced Concrete (SFRC) and exhibits superior properties in terms of ductility, fracture energy, toughness, strength and durability due to the addition of steel fibers when compared to conventional concrete. SFRC has a varied application area. In practice, steel fibers which have different lengths, diameters, and aspect ratios are used. These variable characteristics of steel fibers have highly influence on the performance of SFRC. The goal of this study is aimed at creating a standard foresight in determining the fiber types by comparing the steel fiber types which have the same tensile strengths and different lengths, diameters, and aspect ratios. For this purpose, the series of SFRC specimens which have the same concrete mixing ratios were produced by using steel fibers which have the same tensile strengths and different lengths, diameters, and aspect ratios. The fresh properties of the produced SFRC specimens were determined by the Slump test. The hardened properties were determined by compressive and flexural strength tests. It was shown that the fresh and hardened properties of the SFRC specimens were changed by steel fibers that had the same shapes, tensile strengths and different lengths, diameters, and aspect ratios. The optimum steel fiber types were determined according to the targeted fresh and hardened properties of SFRC

Reactive extrusion of poly(ethylene terephthalate)-(ethylene/methyl acrylate/glycidyl methacrylate)-organoclay nanocomposites

This study was conducted to investigate the effects of component concentrations and addition order of the components on the final properties of ternary nanocomposites composed of poly(ethylene terephthalate), organoclay, and an ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer acting as an impact modifier for PET. In this context, first, the optimum amount of the impact modifier was determined by melt compounding binary PET-terpolymer blends in a corotating twin-screw extruder. The amount of the impact modifier (5 wt%) resulting in the highest Young's modulus and moderate elongation at break was selected owing to its balanced mechanical properties. Thereafter, by using 5 wt% terpolymer content, the effects of organically modified clay concentration and addition order of the components on the properties of ternary nanocomposites were systematically investigated. Mechanical testing revealed that different addition orders of the materials significantly affected the mechanical properties. Among the investigated addition orders, the best sequence of component addition (PI-C) was the one in which poly(ethylene terephthalate) was first compounded with E-MA-GMA. Later, this mixture was compounded with the organoclay in the subsequent run. In X-ray diffraction analysis, extensive layer separation associated with delamination of the original clay structure occurred in PI-C and CI-P (Clay + Impact Modifier followed by PET) sequences with both 1 and 3 wt% clay contents. X-ray diffraction patterns showed that at these conditions exfoliated structures resulted as indicated by the disappearance of any peaks due to the diffraction within the consecutive clay layers

Effect of impact modifier on the properties of poly (ethylene terephthalate)-organoclay nanocomposites

The effects of component concentrations and addition order of the components, on the final properties of ternary nanocomposites composed of amorphous poly (ethylene terephthalate) matrix, organically modified clay, and an ethylene / methyl acrylate / glycidyl methacrylate (E-MAGMA) terpolymer were studied. All formulations were prepared by melt compounding of the components with a two-step mixing procedure in a corotating twin-screw extruder. Considering the X-Ray Diffraction, SEM, impact and strain at break results, the best sequence of component addition was the one in which PET was first compounded with E-MA-GMA, later this mixture was compounded with the organoclay in a subsequent run. In this mixing order, the polymer-impact modifier matrix mixture prepared in the first extrusion run has higher melt viscosity than pure PET, thus this matrix can apply high shear stresses on the clay particles and delaminate the clay layers resulting in the best mechanical properties

Two new cases with costello syndrome

Costello syndrome (CS) was described in 1977 by Costello who reported two unrelated children with a new syndrome comprising short stature, redundant skin of the neck, palms, soles, and fingers, curly hair, papillomata around the mouth and nares, and mental retardation. Several additional cases have been reported since then.  Herein we report two patients with Costello syndrome; one of these patients had associated mesenteric cyst

Interface-driven phase-separated coatings

A homogeneous mixture of two polymers dissolved in a common solvent or a mixture of solvents was applied as a thin film. The first component was a bisphenol-A based epoxide derivative modified with tetraethoxysilane (TEOS) oligomer and the second component was a high-solids fluorinated acrylic copolymer. The thin films were coated on steel substrates and were thermally crosslinked using a methylated melamine formaldehyde and/or a polyamide-amine curing agent. The films were evaluated via x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) with integrated energy dispersive spectroscopy (EDS). It was found that the molecular weight of the resins, fluorine content, epoxide inorganic modification, and curing agent affected the degree of stratification

Aviation: Thermoplastic and Thermoset Polymers in

WOS: 000489145500013This chapter presents a review of polymers and composites used in the aviation industry with new developments and standard protocols. This chapter will enable the readers to understand the aviation industry from a polymer and materials science perspective. It helps to understand the rapid growth of the aviation industry with high demand of lightweight structures. the chapter deals with all aspects of polymers including thermoplastics, thermosets, and composites. Qualification tests and some tests are given to get a better understanding of polymeric materials used in the aviation industry. Finally, some recent new developments are presented with a futuristic outlook