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Işıl işlem uygulamasının lifli beton özelliklerine etkisi

Influence of heat treatment application on properties of fiber reinforced concrete

  1. Tez No: 39263
  2. Yazar: OSMAN ÜNAL
  3. Danışmanlar: PROF.DR. MEHMET UYAN
  4. Tez Türü: Doktora
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1994
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 129

Özet

ÖZET Bu çalışmada, betonun erken yaşlardaki mukavemet gelişimini hızlandırmada yararlanılan ısıl işlemlerin lifli betonlara uygulanması halinde, lifli betonun erken ve ileriki yaşlardaki elastik ve elastik olmayan özelliklerine etkisi araştırılmıştır. Bu çalışmada beton numuneleri, karışım agregasının granülometri eğrisi TS 706 standardına göre (A-[q“ B-|6) referans eğrileri arasında kalacak şekilde ayarlanılarak üretilmiştir. En büyük agrega boyutu, granülometrisi ve su/çimento oranları sabit olup betona katılan lif miktarları sırasıyla 0, 2.5, 5, 8 ve 10 dm3 / m3 olan 5 farklı bileşimde beton üretilmiştir. En yüksek lif miktarına ait beton karışımının kıvamı kuru-plastik en düşük lif miktarına ait beton karışımının kıvamını akıcı hale getiren su / çimento oranının 0.63 olduğu tespit edilmiş ve tüm beton karışımlarında bu oran sabit tutulmuştur. Üretildikten hemen sonra 20°C de havada bekletilen numunelere ”20°C de saklanmış“ adı verilmiştir. Uygulanan ısıl işlem çevrimlerinin ön bekleme süreleri, ısınma ve soğuma hızları, ısıl işlem sıcaklıkları ve bu sıcaklıkta bekleme süreleri birbirinden tamamen farklıdır. Bunlardan ısıl işlem sıcaklığı 50°C olana ”Yumuşak çevrim“, 65°C olana ”Ilımlı Çevrim“ ve 80°C olanada ”Sert Çevrim" adı verilmektedir. Üretilen prizmatik numuneler üzerinde 1., 28 ve 90. günlerde ultrases hızı tayini, eğilme ve basınç mukavemeti deneyleri yapılmıştır. Ayrıca 28. günde kılcallık ve su emme özellikleri tayin edilmiştir. Silindirik numuneler üzerinde ise 28 ve 90. günlerde kısa süreli basınç deneyleri yapılarak ısıl işlem uygulanan lifli betonların elastik ve inelastik özellikleri araştırılmıştır. Deneyler sonucunda, çalışmada elde edilen sonuçlar şöyle özetlenebilir. Betona katılan lifler, taze betonun işlenebilme özelliğini azaltmaktadır. Şahit ve lifli betona uygulanan çevrimin ısıl işlem sıcaklığı artıkça, 1 günlük numunelerin basınç mukavemeti, eğilme mukavemeti, ultrases hızı ve lif-matris aderans dayanımı artmıştır. Betonun ilk üç özelliğine sert çevrim uygulaması 1. günde diğer kür uygulamalarına oranla en olumlu sonuçları vermiştir. Ayrıca liflerin yukarıda belirtilen özellikler üzerindeki artırıcı etkisi ısıl işlem sıcaklığı 50°C den itibaren azalmıştır. Yine liflerin mukavemeti artırıcı etkisi ısıl işlem sıcaklığı yükseldikçe ilk yaşlarda hem eğilme mukavemetinde nemde basınç mukavemetinde azalmasına karşılık, ileriki yaşlarda eğilme mukavemeti üzerine etkisi sabit kalırken, basınç mukavemetinde azalma devam etmiştir. 20°C de saklanan numunelerde lif miktarının sağladığı mukavemet artışı eğilme mukavemetinde betonun yaşı ilerledikçe azalmasına karşılık basınç mukavemetinde 28 günden sonra sabit kalmıştır. Birinci günde ve ileriki yaşlarda ısıl işlem uygulamasının etkisi basınç mukavemetinde eğilme mukavemetine göre daha fazla olmuştur. Liflerin etkisi ise en fazla eğilme mukavemetini artırmıştır. Şahit ve lifli betonların ultrases hızları erken yaşlarda ısıl işlem sıcaklığı artıkça 20°C ye göre artmıştır. İleriki yaşlarda hem 20°C de saklanmış hemde ısıl işlem görmüş betonların ultrases hızları lif miktarının artmasıyla azalmaktadır. Isıl işlemler betonun kılcallık özelliğini 20°C de bekletilmiş numunelere göre azaltırken görünen porozite oranını artırmıştır. Betonun elastik ve inelastik özelliklerinden süreksizlik sınırı ve elastisite modülü bütün çevrimlerde lif miktarının artması ile azalmıştır. Buna karşılık lif miktarının artması betonun enerji emme kapasitesini artırdığından kırılma şekil değiştirme işi ve basınç dayanımındaki birim kısalma da artmaktadır. Araştırma sonuçlarına göre ısıl işlem uygulamasının lifli beton özellileklerine gösterdiği etkiler normal betonlara göre farklı bulunmuştur. xi -

Özet (Çeviri)

SUMMARY INFLUENCE OF HEAT TREATMENT APPLICATION ON PROPERTIES OF FIBER REINFORCED CONCRETE In this study, the influence of heat treatment application on the properties of fiber reinforced concrete at early and later ages have been investigated. Steel fibrous conrete is composed of cement, aggregate, sand, water and steel fiber which, at first sight, is quite similar to normal reinforced concrete, with one exception the latter does not contain any fiber. The charecteristics of fibrous concrete are as follows; - high degree of toughness as compared to the brittleness of plain concrete - enhanced shock absorbing capability - enhanced fatigue strength - enhanced fiexural strength Because of these, in general, fiber reinforced concretes are used in the industrial floor slabs, concrete pavements, shotcrete, concrete pipes, refractory concrete and precast concrete products. The purpose of heat treatment is to accelerate strength development of concrete at early ages. It is well known that the higher temperatures accelerate the hydration reactions responsible for the strength gain. In addition it makes casting in the precast works and the construction site largely independent of the weather. No modern concrete works should therefore be without a heating system for concrete hardening. Different systems are in the mean time available on the market so that an optimal solution can be found for every application. The proper heating system can thus only be selected following thorough analyses at the intended location and comprehensive consultation. The increasing utilization of concrete in industrial and private building projects is due in no small measure to the increase of early xiistrength of concrete that was achived during the past few decates. Efforts to attain increasingly higher early strengths are aimed at raising the productivity in concrete construction still further. Through the acceleration of the development of strength at an early concrete, age, contunious production processes are possible in particular in the manufacture of serial parts. In this way, the major part of all concrete production activities at the construction site and in the precast works will become independent of seasonal temperature fluctuations. An increase of early strength of concrete can be achived through. - utilization of rapid hardening cements - as low water-cement ratios as possible - use of accelerators - heat treatment The most widely used method among these is steam curing under atmospheric pressure, in other words“Application of Heat Treatment”. Steam curing causes some reduction in strength of concrete at later ages, while increasing the early strength. This act was explored by many researchers for normal concrete containing normal cement contents. By this study, it was tried to find out the influence of steam curing on the properties of fiber reinforced concrete at early and later ages. The study is presented in 5 chapters. In the first chapter general knowledge about the subject, definitions, related literature, the purpose and the necessity of the study are given. The charecteristics of the concrete compositions, the proportions of concrete mixes, the methods of preparations and curing of concretes are given in the second chapter. The different types of heat treatment cycles and the experimental technigues used in tests are also given in the second chapter. The test results obtained of hardened concrete are listed and necessary explications are given in the third chapter. Appraisals of test results and their discussion on the effect of the heat treatment are the subjects of the fourth chapter. The conclusions evolved from the study and proposals for further investigations are given in the last chapter. Grading curves of the aggregate mixtures have been regulated so as to be between (A-|6 - B-|6) curves according to T.S. 706 standart. The maximum aggregate size and grading of aggregate and effective W/C were kept constant. The fiber content of mixtures was changed from 0.0 dm3/m3 up to 10 dm3/m3 at 2.5 dm3/m3 intervals. The optimum W/C was obtained as 0.63 for all mixtures. To give acceptable consistency of fresh concretes. Normal portland cement (PC 32.5) was used. XIIIVe-Be time, Inverted slump cone time, slump and unit weight tests have been performed on the produced concrete mixtures. After these experiments, fibrous concrete which are placed in their moulds have been placed in the air conditioner for heat treatment cycles. Different heat treatment cycles have been applied by varying the presteaming period-holding, preset temperature rise period, maximum temperature period-heat treatment temperature-and cooling period and also total cycling period. When presteaming period is 4 hours, heating and cooling rate 10°C/h, maximum temperature 50°C and the total cycle time 22 hours, that cycle has been called“Long or soft cycle”. When presteaming periods are 2 and 1 hour, heating and cooling rates 20°C/h and 30°C/h, maximum temperatures 65°C and 80°C and the total cycle times 10.5 hours and 8 hours, those cycles were called“moderate”cycle and“Short-hard”cycle, respectively. After completion of heat treatment cycles, test specimens have been cured at laboratory atmosphere of 20°C temperature and 60±5% relative humidity till the testing day. They were tested in order to demonstrate the influence of the heat treatment cycles on the properties of fiber reinforced concrete compared to normal concrete. The parameters of the heat treatment cycles, have been shown in table 1. and in Figure 1. Table 1 - Properties of Cycle Parameters XIVTEMPERATURE 80 - Figure 1 - Applied Heat Treatment Cycles. On the hardened concrete specimens, the same testing program has been repeated at the ages of 1., 28 and 90 days nine prismatic specimens of 7x7x28 cm. dimensions had been manufactured from each mixture. The ultrasonic velocity was measured at the ages of 1, 28 and 90 days on prismatic specimens in the usual manner. Then the same specimens have been tested under three point loading and the modified compressive strength tests were conducted on their broken pieces. Just at the age of 28 days, after beam flexure test has been performed, the durability and water absorption test were done on the other half of broken pieces. In order to investigate the mechanical behaviour of the heat-treated congrates, short-term compressive loading have been performed on the cylindirical specimens at the ages of 28 and 90 days. The result of these experiments have been used to investigate the effects of the heat treatment application to elastic and inelastic properties of FRC. The variation of concrete properties with the change in fiber content of concrete and with the application of heat treatment were shown on the graphs and the evaluations and discussions were based on these graphs. Important results obtained in this study can be grouped as follows: A) Results related with the fresh concretes 1) Factors that influence the behaviour of freshly mixed SFRC include matrix composition, fiber type, fiber volume fraction and fiber matrix interfacial bond characteristics. xvAs mentioned earlier, addition of fibers will make the composite stiff e r. In this study it was observed that fibers, which have been added to concrete, decreased workability. B) Results related with the properties of hardened concrete 1) Results related with fiber-matrix bond strength of composites. a) Although, heat treatment application increases bond strength of 1-day old specimens compared to those kept at 20°C, the stuation for 28 and 90. day old specimens were reversed. This may be explained by defects a rising from inclusion of increasing amount of fibers in concrete. b) The rate of fiber-matrix bond strength development tends to increse in earlier ages and decrease in later ages. 2) Results related to flexural strength. a) The highest strength values at the age of 1 day were obtained when the short cycle has been applied. It has been that when the heat treatment tempareture was increased, the flexural strength of controll and fibrous concretes have increased at the firstday and 28th days, with respect to values of specimens kept at 20°C tempereture. 90 day specimens have shown values lower than others. It's known that rapid hydration may cause a reduction in the strenght usually attained at later ages when steam curing-heat treatment-applied. But in this study, later age strength of heat treatment applied concrete was not lower than control concrete. Keeping the specimens in the air, and not in water. b)lt may be an explanation for this result that increasing of added fiber amount in specimens both kept at 20°C and heat treated increased the flexural strength at earlier and later days. c) Rate of increase in the flexural strength of fibrous and control concretes, decreases with heat treatment temperature higher than 50°C. But for specimens at later ages, it was similar to the specimens kept at 20°C. 3) Results related to compressive strength a) In general, heat treatment of fibrous concretes effect the flexural strength and the compresive strength in the same manner. xvib) The 1 day relative compression strength of fibrous concrete was influenced in positive direction from heat treatment, c) The results have shown that rate of increase of compressive strength is higher than rate of increase of flexural strength for 1 -day specimens. d) It has been seen that the highest increases in compressive strength of 1. 28 and 90 day specimens by the increasing amount of fibers have been obtained in specimens kept at 20°C. 4) Results related to ultrasound velocity a) The 1 day relative ultrasound velocity of concrete was influenced by the heat treatment in the same manner with compressive and flexural strength of concrete. b) Ultrasound velocity decreases with increasing amount of fiber at 28 and 90 days both at 20°C and when heat treatment applied. c) The good correlation between the result from ultrasound velocity and compressive strength test of heat treated concretes shows that the measuring of ultrasound velocites gives meaningfull results in determining the strengh. 5) Results related to capilarity a) Heat treatment application decreases capilarity of control and fibrous concretes at the age of 28. 6) Result related with inelastic behaviour a) increasing the fiber contend of cocretes decreases the modulus of elasticity and, discontinuity limit of 28th and 90th day specimens at 20°C but increases the loosening point strain at compressive strength, and ultimate strength. XVil

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