Effect of pozzolanic materials on the mechanical properties and chloride diffusivity of concrete

Yapılan deneysel çalışmada iki farklı seri beton üretildi. İlk seri betonlarda; portland çimentosu ince öğütülmüş F tipi uçucu kül ile yerdeğiştirildi, ikinci seri betonlarda ise çimentonun yerdeğiştirilmesi ince öğütülmüş yüksek fırın cürufu ile yapıldı. Çalışmanın ilk bölümünde ince öğütülmüş (Blaine özgül yüzeyi 604 m2/kg) uçucu kül miktarının betonun basınç dayanımına ve hızlı klor geçirimliliğine etkisi incelendi. Sabit 0.35 su/bağlayıcı oranında betonlar üretilerek her üretimdeki toplam bağlayıcı madde miktarı sabit tutuldu ve uçucu kül çimento ile %70’e kadar yerdeğiştirilerek kullanıldı. Uçucu külün çimentoyla yerdeğiştirilmesi bire bir ağırlık esasına göre ve %10’luk adımlarla yapıldı. Üretilen betonların çeşitli yaşlarındaki basınç dayanımları bulundu. Bu betonların üzerinde ayrıca ASTM C 1202 standardına göre hızlı klor geçirimlilik deneyleri de yapıldı. Çimentonun % 40 oranında ince uçucu külle yerdeğiştirilmesi durumunda beton basınç dayanımları yaklaşık aynı oldu. Betonda ince öğütülmüş uçucu kül kullanımı ile klor geçirimlilikleri önemli ölçüde azaldı. Çalışmanın ikinci bölümünde ise; aynı su/çimento oranına sahip betonlarda, çimento ince öğütülmüş yüksek fırın cürufu ile %40, %60 ve %80 oranlarında yerdeğiştirildi. Blaine özgül yüzeyi 5000 cm2/gr olan cürufun çimentoyla yerdeğiştirmesi yine bire bir ağırlık esasına göre yapıldı. Üretilen bu betonlarda ise klor iyonu yayınımı ve elektriksel özdirenç deneyleri yapıldı. Elde sonuçlar cüruf ilave edilmesinin betonların klor iyonu geçirimliliklerinin önemli oranda azalttığını ortaya koydu. Cüruf içeren betonların elektriksel özdirençleri de, sadece portland çimentosu ile üretilen betonlara göre büyük oranlarda arttı. Elektriksel özdirenç ölçümlerinin, yapı inşaa sürecinde, elde edilen beton klor geçirimliliklerinin izlenmesi ve kalite kontrolü için uygun bir yöntem olduğu sonucuna varıldı.  Anahtar Kelimeler: Puzolan, mekanik özelikler, dürabilite, klor yayınımı, elektriksel özdirenç.The primary objective of the present work is to study the effects of pozzolans on the mechanical and durability properties of concrete. Fly ash and granulated blast furnace slag were used in the study. In order to utilize the potential of these materials and obtain better concrete performance, pozzolans with smaller particle sizes were used, which were obtained by grinding. The experimental study consists of two parts. In the first part, effects of ground fly ash on the concrete properties were investigated. The effect of ground granulated blast-furnace slag on the chloride diffusivity of concrete was the main focus of the second part of the study. In the first part, a coarse F type fly ash was ground to a Blaine surface area of 604 m2/kg. The test results show that the physical properties such as density and fineness changed. The physical changes due to grinding are: i) the fineness of fly ash increases, ii) there is a remarkable increase in density by reducing the porosity of the fly ash particles, iii) the spherical fly ash particles transform into the mostly irregular shapes; some small fly ash particles keep their original shapes. For investigating the effects of ground fly ash, eight concrete mixtures were prepared using the same batch of ordinary portland cement (OPC) and ground low-lime fly ash. The aggregate grading used in the mixtures of concrete, water-binder ratio, and the maximum particle size of aggregate were kept constant in all concretes, but the partial replacement of cement by fly ash was varied from 0 % (OPC concrete) to 70 %, in steps of 10 %. The replacement was on one to one weight basis. Compressive strengths of the concretes were obtained for different ages. Rapid chloride permeability test was also carried out on the 1 year old specimens. At 28 days, there was little reduction in compressive strength up to 40 % cement replacement by ground fly ash; then significant decrease was recorded for the further fly ash dosages. At 56 and 120 days, however, the compressive strength up to 40 % cement replacement by fly ash was almost identical to that of the no fly ash concrete and for one year it was even higher. Beyond 40 % replacement, the compressive strength decreased significantly for the age of 1 year. The results of the rapid chloride penetration tests indicated that high volume ground fly ash concrete had much better resistance to the penetration of chloride ions. The main objective of the second part of the experimental study was to investigate the effect of ground granulated blast-furnace slag on the chloride diffusivity of concrete. Concretes with constant water/binder ratio were produced, in which an ordinary portland cement was partially replaced by a ground granulated blast-furnace slag with the replacement ratios of 40%, 60% and 80%, respectively. The slag used had a high fineness with a Blaine specific surface of 5000 cm2/gr. Accelerated chloride diffusivity tests based on migration testing were carried out on the concretes. In parallel, testing of electrical resistivity was also conducted. The resistivity of the concretes were obtained by two different test methods; i) two electrode method, and ii) four electrode method. The concretes containing granulated blast - furnace slag showed a significantly better resistance against chloride penetration when compared to that of the pure portland cement. Results proved that slag replacement ratio is a major factor for reducing the chloride diffusivity and the diffusivity decreased with the increasing slag amount. Incorporation of slag had an important effect also on the electrical resistivity of concrete and the resistivity of the concretes containing slag were substantially higher than that of the portland cement concrete. This increase in resistivity became more distinct with the increase in replacement ratio. For a given type of concrete and test conditions, the test results confirmed that there is a linear relationship between chloride diffusivity and electrical resistivity. Hence, as soon as this relationship is established, the test results also confirmed that a monitoring of electrical resistivity may be a very appropriate way for monitoring the chloride diffusivity as part of a general quality control during the concrete construction.   Keywords: Pozzolan, mechanical properties, durability, chloride diffusivity, electrical resistivity

Thermal and Compressive Strength Properties of Sepiolite Substituted Autoclaved Aerated Concrete

Gazbeton gözenekli hafif betondur. Bu araştırmada, Sepiyolitin gazbeton üretiminde hammadde olarak kullanılan kuvarsit yerine ikamesinin gazbetonun ısıl ve basınç dayanım özelliklerine etkisi araştırılmıştır. Araştırmada, duvar elamanı olarak kullanılan ve ticari olarak üretimi yapılan G2/04 sınıfı gazbeton üretimi esas alınmıştır. Eskişehir Sivrihisar maden sahasından alınan Sepiyolitin, hammadde olarak kullanılan kuvarsit yerine %5, %10, %15, %20 ve %25 oranlarında ikame edilerek gazbeton örnekleri üretilmiştir. Üretilen örnekler 60 ºC sıcaklıkta 4 saat kürde bekletildikten sonra 180 ºC'de 11 bar basınçta 6,5 saat otoklavda küre tabi tutulmuştur. Üretilen örneklerin basınç dayanımı ve ısıl iletkenlik özellikleri belirlenmiştir. Sonuç olarak sepiyolit oranının arttırılması sonucu basınç dayanımında azalma olurken ısıl iletimde iyileşme gözlenmiştir.Aerated concrete is a lightweight concrete which has porous structure. In this study, effects of usage of sepioliteas a raw material instead of quartzite on the thermal and compressive strength properties of aerated concrete were investigated.G2/04 class aerated concrete, which has been commercially produced as a wall component, has been focused. Aerated concrete samples have been prepared by substitution of sepiolite instead of quartzite in %5, %10, %15, %20 and %25. Sepiolite has been provided from Eskişehir mine field. After 4 hours cure at 60ºC, samples moved to treat in autoklave in the temperature of 180ºC and pressure at 11 bar for 6.5 hours. Thermal conductivity and compressive strength properties of samples were determined. As a result, increasing the rate of sepiolite in aerated concrete decreases the compressive strength and increases the thermal conductivity

Self-cannibalism: The man who eats himself

Self-mutilation is a general term for a variety of forms of intentional self-harm without the wish to die. Although there have been many reports of self-mutilation injuries in the literature, none have reported self-cannibalism after self-mutilation. In this article we present a patient with selfcannibalism following self-mutilation. A 34-year-old male patient was brought to the emergency department from the prison with a laceration on the right leg. Physical examination revealed a well-demarcated rectangular soft tissue defect on his right thigh. The prison authorities stated that the prisoner had cut his thigh with a knife and had eaten the flesh

Deindustrialization in cities of the global south

Recent research by economists has shown that deindustrialization is more severe in Sub-Saharan Africa and Latin America than it ever was in the Organisation for Economic Co-operation and Development (OECD). Nevertheless, most research on deindustrialization is focused on the former centres of Fordist manufacturing in the industrial heartlands of the North Atlantic. In short, there is a mismatch between where deindustrialization is researched and where it is occurring, and the objective of this paper is to shift the geographical focus of research on deindustrialization to the Global South. Case studies from Argentina, India, Tanzania and Turkey demonstrate the variegated nature of deindustrialization beyond the North Atlantic. In the process, it is demonstrated that cities in the Global South can inform wider theoretical discussions on the impacts of deindustrialization at the urban scale

Existence of large-data global weak solutions to a model of a strain-limiting viscoelastic body

We prove the existence of a unique large-data global-in-time weak solution to a class of models of the form utt=div T+f for viscoelastic bodies exhibiting strain-limiting behaviour, where the constitutive equation, relating the linearised strain tensor ε(u) to the Cauchy stress tensor T, is assumed to be of the form ε(ut)+αε(u)=F(T), where we define F(T)=(1+|T|a)−1aT, for constant parameters α∈(0,∞) and a∈(0,∞), in any number d of space dimensions, with periodic boundary conditions. The Cauchy stress T is shown to belong to L1(Q)d×d over the space-time domain Q. In particular, in three space dimensions, if a∈(0,27), then in fact T∈L1+δ(Q)d×d for a δ>0, the value of which depends only on a

Association between Stargardt's disease and Retinitis Pigmentosa: Is common genetic mutation responsible? [Stargardt hastali?i ve Retinitis Pigmentosa birlikteli?i: Ortak genetik mutasyon mu sorumlu?]

In this study the association between Stargardt's disease (STGD) and Retinisitis Pigmentosa (RP), both of which is seen in a case with a mutated ABCA4 gene, is analysed. Fundus exaimination was performed to a 23 years old male whose dark vision are severely impaired and found beaten metal appearance on his right and left macula with bony specules in peripheral retina. Therefore fundus fluorescein angiography and electrophysiologic tests was performed to him. He was diagnosed with both STGD and RP based on clinical and diagnostic test findings. Genetic research of the patient revealed a mutation in ABCA4 gene. We consider that a possible association between STGD and RP in patients diagnosed with STGD or RP and that the major role of genetic research in diagnosis of retinal diseases should be kept in mind