Makale Koleksiyonu

Bu koleksiyon için kalıcı URI

https://hdl.handle.net/11491/3677

Listeleniyor 1 - 12 / 12

Role of matrix structure and flaw size distribution modification on deflection hardening behavior of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC)
(Central South University of Technology, 2019) Tosun Felekoğlu, Kamile; Gödek, Eren
The multiple cracking and deflection hardening performance of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC) under four-point flexural loading have been investigated. Matrices with different binder combinations and W/B ratios (from 0.44 to 0.78) providing satisfactory PVA fiber dispersion were specially designed. Effect of pre-existing flaw size distribution modification on deflection hardening behavior was comparatively studied by adding 3 mm diameter polyethylene beads into the mixtures (6% by total volume). Natural flaw size distributions of composites without beads were determined by cross sectional analysis. The crack number and crack width distributions of specimens after flexural loading were characterized and the possible causes of changes in multiple cracking and deflection hardening behavior by flaw size distribution modification were discussed. Promising results from the view point of deflection hardening behavior were obtained from metakaolin incorporated and flaw size distribution modified PVA-ECCs prepared with W/B=0.53. The dual roles of W/B ratio and superplasticizer content on flaw size distribution, cracking potential and fiber-matrix bond behavior were evaluated. Flaw size distribution modification is found beneficial in terms of ductility improvement at an optimized W/B ratio.
Çoklu çatlayan lifli kompozitlerin birim şekil değişiminin dijital görüntü korelasyonu ile analizi: Parametre etkilerinin değerlendirilmesi
(TMMOB İnşaat Mühendisleri Odası, 2020) Yıldırım, Tarık; Keskinateş, Muhammer; Gödek, Eren; Tosun Felekoğlu, Kamile; Felekoğlu, Burak; Önal, Okan
Bu çalışmada çekme yüklemesi altında çoklu çatlak davranışı sergileyen lifli kompozitlerin birim şekil değiştirmeleri geleneksel deformasyon ölçer (LVDT) ve dijital görüntü korelasyonu (DIC) yöntemiyle incelenerek kıyaslanmıştır. DIC yönteminde ışık etkisi (kontrollü aydınlatma varlığı), görüntü çözünürlüğü, alt küme boyutu ve adım aralığı parametreleri ile iki farklı korelasyon yöntemi dikkate alınarak analizler gerçekleştirilmiştir. Uygun alt küme boyutunun seçilmesi ve görüntülerin kontrollü aydınlatma ile yüksek çözünürlük koşullarında alınması durumunda, DIC analizi sonucu elde edilen birim şekil değiştirme değerleri, LVDT’lerden elde edilen değerler ile örtüşmektedir.
Behaviour of brick infill walls strengthened with expanded steel plates
(Springer Netherlands, 2016) Cumhur, Alper; Altundal, Adil; Kalkan, İlker; Aykaç, Sabahattin
The present study was dedicated to investigate an effective, economical and convenient method for strengthening brick infill walls, i.e. the use of externally-bonded expanded steel plates. A total of 30 plastered wall assemblies were tested under monotonic diagonal loading to investigate the contribution of these plates to the load capacities, ductilities and rigidities of brick walls. The plate thickness, bolt spacing and location of the plates in the wall were the parameters of the test program. The experiments indicated that application of the plates on the outermost fine plaster layer significantly improves the diagonal load–deflection behaviour of infill walls and reducing the bolt spacing provides the strengthened walls with higher load capacity values. An analytical expression was developed for estimating the diagonal load capacities of plated brick walls. The analytical load estimates were found to be in close agreement with the experimental values. © 2016, Springer Science+Business Media Dordrecht.
Permeability characteristics of superfine cement-grouted sand
(American Concrete Institute, 2017) Avcı, Eyübhan; Mollamahmutoğlu, Murat
The aim of this research was to investigate the permeability of superfine cement-grouted sand. Initially, rheology of superfine cement suspensions was studied. The sedimentation and the setting time increased but the viscosity decreased as the water-cement ratio (w/c) increased. In addition, the penetrability of superfine cement suspensions with different w/c into various graded sand specimens prepared at different relative densities was tested. The penetrability of suspensions into the sand specimens was successful and increased as the w/c increased, but decreased as the relative density increased. Grouted sand samples were kept in a humidity room at a temperature of 20°C (68°F) until testing time and subjected to permeability tests at different time intervals. The coefficient of permeability increased as the w/c increased, but decreased as the relative density and the percentage of fines increased. Additionally, the coefficient of permeability of grouted samples decreased slightly with time. Copyright © 2017, American Concrete Institute. All rights reserved.
A betonului autocompactant increasing the tensile strength of fiber reinforced self-compacting-concrete, and effects of fiber type and orientation
(Fundatia Serban Solacolu, 2017) Korkmaz, Selim Deniz; Birinci, Fahri
In this study, the effects of using fiber in self compacting concrete (SCC) on flow parameters, tensile and compressive strength of concrete were investigated. Unit weight, air content, slump flow, J-ring, V-funnel tests on fresh concrete and compressive, splitting tensile along with flexural strength tests on hardened concrete were performed, in addition fresh and hardened concrete properties were studied for to determine the relationship between them. A polypropylene fiber, an alkaliresistant glass fiber and two types steel fibers which have the different lengths and the different length/diameter ratio were used in the test specimens. It is observed that an increase in the amount, length and length/diameter ratio of steel fibers resulted in an increase of the tensile strength of concrete (more than 90% in flexural tensile strength according to non-fiber concrete series), while, properties of fresh concrete deteriorated and compressive strength of concrete decreased. © 2017, Fundatia Serban Solacolu. All rights reserved.
Syneresis effect on the permeability of chemically grouted sand
(Geological Society of London, 2016) Mollamahmutoğlu, Murat; Avcı, Eyübhan
The aim of this research was to investigate the permeability of sodium silicate grouted sand specimens having various gradations and relative densities. Initially, rheological properties of sodium silicate grouts were studied. The gel time decreased as the sodium silicate content increased. Viscosities of sodium silicate grouts increased as the silicate content increased. Syneresis of sodium silicate grout gels increased with the increase of silicate content up to a point and then started decreasing sharply. The penetrability of chemical grouts with different sodium silicate contents into various graded sand specimens prepared at different relative densities was highly successful. Grouted sand samples were kept in humid conditions at a temperature of 20°C until testing time and were subjected to permeability tests at different time intervals. In general, sodium silicate grouting reduced the permeability of various graded sand specimens. The permeability of grouted sand specimens slightly increased with time as a result of syneresis. © 2016 The Author(s).
Çimento esaslı lifli kompozitlerin dijital görüntü korelasyonu yöntemi ile çoklu çatlak davranışının incelenmesi
(Gazi Üniversitesi, 2019) Yıldırım, Tarık; Felekoğlu, Kamile T.; Gödek, Eren; Keskinateş, Muhammer; Felekoğlu, Burak; Önal, Okan
Dijital görüntü korelasyonu (DIC), matematik tabanlı temassız bir deformasyon ölçüm tekniğidir. Mühendislik özellikleri geliştirilmiş çimentolu kompozitler (ECC) geleneksel lifli kompozitlerden farklı olarak kararlı çoklu çatlama davranışı göstermektedir. Bu kararlı çoklu çatlama davranışının analizi, kompozitin mekanik ve durabilite performansının değerlendirilmesi açısından oldukça önemlidir. Bu çalışmada, DIC'in mühendislik malzemelerinin deformasyon ölçümleriyle ilgili uygulama alanları detaylı bir literatür taramasıyla sunulmuştur. ECC’nin çoklu çatlak davranışının analizi ile ilgili yapılan çalışmalar taranmış ve DIC yönteminin bu amaçla kullanılabilirliği deneysel olarak incelenmiştir. Bu kapsamda yüksek çekme dayanımlı polipropilen lif kullanılarak kemik şeklinde çekme numuneleri üretilmiştir (HTPP-ECC). Kompozitlerin çekme yüklemesi altındaki deformasyonları numune etrafına yerleştirilen 4 adet geleneksel deformasyon ölçer (LVDT- Linear variable differential transformer) ve DIC tabanlı bir kamera sistemiyle kaydedilmiştir. LVDT ve DIC yöntemleri ile elde edilen bulgular kıyaslanarak, DIC tekniğinin kompozitlerin çoklu çatlama davranışının incelenmesinde kullanılabilirliği araştırılmıştır. Sonuç olarak, DIC’nin ECC’lerde deformasyon ölçümü açısından LVDT’lerle yakın sonuçlar verdiği ve çatlak analizi avantajıyla geleneksel yöntemlerden üstün yanları olduğu tespit edilmiştir.
Ultrafine Portland cement grouting performance with or without additives
(Springer Verlag, 2014) Mollamahmutoğlu, Murat; Avcı, Eyübhan
The aim of this experimental study was to investigate the penetrability of ultrafine Portland cement suspensions with or without additives into sand specimens and the strength and permeability of grouted sand samples. It was shown that ultrafine Portland cement grouts with dispersive agent could be used to treat not only medium to fine sand but also 100% fine sand where chemical grouts can only penetrate The basic rheological properties of ultrafine Portland cement suspensions with or without additives were studied. The penetration performance of suspensions into various graded medium to fine sand specimens prepared at different relative densities was examined. The unconfined compressive strength and the permeability characteristics of sand specimens permeated with ultrafine Portland cement suspensions with or without additives were searched at different time intervals. © 2015, Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg.
UCS properties of superfine cement-grouted sand
(American Society of Civil Engineers (ASCE), 2016) Avcı, Eyübhan; Mollamahmutoğlu, Murat
This research focused on the strength characteristics of superfine cement-grouted sand with various gradations and relative densities. At first, grout properties of superfine cement suspensions were studied. The sedimentation and the setting time increased but the viscosity decreased as the water-cement (W/C) ratio increased. Additionally, the groutability of superfine cement suspensions with different W/C ratios into various graded sand specimens having different relative densities was tried. The groutability of suspensions especially into the fine sand specimens was successful with certain W/C ratios and increased as the W/C ratio increased but decreased as the relative density increased. Grouted sand samples remained in tanks filled with water at a temperature of 20°C until testing time and subjected to unconfined compressive strength (UCS) tests at different time intervals. The UCS of grouted sand specimens decreased as the W/C ratio increased, but it increased as the relative density increased. The UCS of grouted fine sand was greater than that of medium sand. Furthermore, the UCS of grouted samples increased with time. © 2016 American Society of Civil Engineers.
Performance of novel chemical grout in treating sands
(American Society of Civil Engineers (ASCE), 2017) Mollamahmutoğlu, Murat; Avcı, Eyübhan; Tomaç, Sercan Kerem; Köse, Dursun Ali
A new chemical grouting formed by sodium silicate-boric acid mixtures was introduced. Initially, suitable sodium silicate and boric acid contents in the grout mixtures were studied. Gel time, initial viscosity, and syneresis properties of adopted grouts were determined. Strength and permeability of grouted sand specimens having different gradation, relative density, curing time, and condition were investigated. Gel time decreased but viscosity increased as the sodium silicate and boric acid contents increased. Syneresis of grouts increased with the increase in sodium silicate and boric acid contents. As the silicate content of the grout solutions increased, the unconfined compressive strengths of the wet-cured and air-dried specimens increased, but decreased with time as a result of syneresis. The permeability of the wet-cured sand specimens decreased by two to three orders of magnitude after grouting; it increased with increasing silicate content but decreased with increasing in boric acid content.
Effectiveness of microfine portland cement grouting on the strength and permeability of medium to fine sands
(Budapest University of Technology and Economics, 2015) Mollamahmutoğlu, Murat; Avcı, Eyübhan
The purpose of this research was to investigate the grout properties of microfine Portland cement whose specific surface area was greater than those of the same kind products frequently cited in the relevant literature. In this regard, viscosity, setting time and stability of microfine cement suspensions were initially studied. It was seen that the sedimentation and the setting time increased but the viscosity decreased as the water/cement (W|C) ratio of microfine Portland cement suspensions increased. In addition, the penetrability of microfine Portland cement suspensions with different W|C ratios into various graded medium-to- fine sand specimens prepared at a relative density of 30% was tested under grouting pressures ranging from 0.25 to 0.5 MPa. It was observed that the penetrability of cement suspensions into the specimens was successful and increased as the W|C ratio increased. All grouted samples were kept in humidity room at a temperature of 20°C until testing time and subjected to permeability and unconfined compressive strength tests at different time intervals. The unconfined compressive strength decreased as the W|C ratio as well as the fine content of sand increased. Permeability tests conducted on grouted specimens with a period of two months revealed that they were impermeable. © 2015, Technical University of Budapest. All rights reserved.
Development of flaw tolerant fiber reinforced cementitious composites with calcined kaolin
(Elsevier Ltd, 2017) Gödek, Eren; Tosun Felekoğlu, Kamile; Keskinateş, Muhammer; Felekoğlu, Burak
Flaws naturally occur in the structure of the cementitious composites or concrete. When brittle composites (ceramics, concrete) are loaded up to their ultimate capacity, micro-cracks initiate and propagate from these flaws in a sudden manner. As an exception, Engineered Cementitious Composite (ECC) surprisingly has an ability to transform its flaw structure into an advantage by exhibiting multiple cracking behavior with improved mechanical properties. On the other hand, presence of polymeric fibers in ECC design can rise some challenging situations such as workability and fiber distribution. Both flaw structure and workability of ECC can be improved by using inert and pozzolanic powders in matrix phase. In this study, five sets of composites were prepared at three different water to cement and fine material to cement ratios by using high tenacity polypropylene fibers (HTPP). Calcined kaolin was used for the first time in order to improve fresh state properties and fiber distribution performance of composites. The flaw tolerances of composites were studied by adding polyethylene beads (diameter of 3 mm by 6% of total volume) as artificial flaws into matrix. Results showed that, flaw tolerant ECCs exhibiting saturated multiple cracking with a flexural strength of 10.9 MPa and a deflection capacity of 13.2 mm can be prepared successfully by using HTPP fibers and calcined kaolin. © 2017 Elsevier B.V.

Güncel Gönderiler