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Hafif ve yarı hafif betonlarda çelik lif kullanımının etkisi

The Effect of the use of steel fibre in the lightweight and semi-light weight concrete

  1. Tez No: 39714
  2. Yazar: MEHMET ALİ YILDIRIM
  3. Danışmanlar: PROF.DR. SAİM AKYÜZ
  4. Tez Türü: Yüksek Lisans
  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: 64

Özet

ÖZET Bu çalışmada ponza taşı ile üretilmiş hafif ve yarı hafif betonlarda çelik lif kullanmanın betonun özelliklerine etkisi araştırılmıştır. Deneysel araştırma için üretilen hafif ve yarı hafif betonlarda agrega granülometrisi, çimento dozajı, su/çimento oranı ve maksimum dane boyutu (16 mm) sabit tutulmuş, çelik lifin hacimce yüzdesi değiştirilmiştir. Normal betonun 4-8 mm ve 8-16 mm boyuttaki bölümü ponza taşı agregası ile değiştirilmek suretiyle elde edilmiş hafif ve yarı hafif betonlar aynı su/ çimento oram ile üretilmişlerdir. Bu şekildeki betonlara değişik oranda çelik lif katılmak suretiyle, aynı özellikteki betonlarda lifin etkisine ortam sağlanmıştır. Böylece elde edilen 11 karışımla standart silindirik numuneler ve prizmalar üretilmiş, 74 gün sonra bu numuneler üzerinde basınç, yarma ve eğilme deneyleri yapılmıştır. Deneysel sonuçlara göre yarı hafif ve hafif betonlarda çelik lif kullanımı ve oranının artürüması bu betonların işlenebilirliğini olumsuz yönde etkilemektedir. Yarı hafif ve hafif betonlarda lif oranının arttırılması bu betonların basınç, yarma ve eğilme dayanımlarını arttırmaktadır. Benzer artışlar bu betonların süreksizlik ve çözülme sınırında da olmaktadır. Lif oranının artürüması yarı hafif betonlarda elastiklik modülünü değiştirmemekte, hafif betonlarda ise bir miktar azaltmaktadır. Yan hafif ve hafif betonlarda lif kullanılması bu betonların basınç dayanımlarındaki şekil değiştirme miktarını ve bu betonların basınç mukavemetine kadar gerilme-şekil değiştirme işini arttırmaktadır. Bu betonlarda lif kullanımı bu betonların ultrases hızlarını değiştirmemektedir. Yan hafif ve hafif betonlarda çelik lif kullanılarak normal betonların mukavemetine yaklaşılmaktadır. Dolayısıyla yapının ağırlığı azaltılarak ekonomik çözümler gerçekleştirmek olasıdır. IX

Özet (Çeviri)

SUMMARY THE EFFECT OF THE USE OF STEEL FIBRE IN THE LIGHTWEIGHT AND SEMI-LIGHTWEIGHT CONCRETE Lightweight aggregate concrete has been used successfully for structural purpose for many years. The own weight of structural concrete represents a very large proportion of the total load in structures and therefore it is advantageous to reduce the density of normal concrete. For structural applications of lightweight concrete, the density of the concrete is often more important than the strength. A decreased density for the same strength level permits a savings in dead load for structural design and foundation. If lightweight concrete is used in concrete construction, a decrease of about 25 % of the total weight in the structural system is obtained which causes a considerable decrease in gravitational and seismic forces. Hence, it is expected that the use of structural lightweight concrete is good solution for the construction of buildings specially in earthquake regions. Following methods are widely used for the production of lightweight concrete : Natural lightweight aggregates of low density are used instead of normal aggregate. Hence, the concrete obtained is know as lightweight aggregate concrete. Lightweight concrete is obtained by introducing large voids within the mortar phase. This kind of concrete is know as aerated, cellular, foamed, or gas concrete. Lightweight concrete is produced by omitting the fine aggregate fractions from the mix, this is described by the name of no-fines concrete. Most of these lightweight concretes are not adequate for structural purposes. Artificial lightweight aggregates such as expanded clay and expanded shale are widely used for structural lightweight concrete, but such aggregates are not yet available in some countries, including Turkey. On the other hand, there are abundant resources of natural pumice lightweight aggregate in Turkey, which has lower strength as compared to artificial ones. In spite of this, it is possible to produce amoderate strength,semi-lightweight concrete, when the pumice lightweight aggregate is combined with normal limestone aggregates in the present work, such a combination of pumice and limestone has been used. The underlying principle of lightweight aggregate concrete is to reduce the density by the introduction of voids in the coarse aggregate itself. This leads to a reduction in many of the physical properties of the concrete. On the other hand, a number of the physical properties may be improved by the introduction of fibres into the concrete. The use of fibre reinforced concrete is gaining increasing importance in the building material area. Hydraulic cements used in building materials are weak in tension, but with the addition of suitable fibres, this difficulty can be overcome. The addition of fibres will also have the following benefits : 1-) Eliminates sudden failure in tension if there is adequate bonding of fibres, 2-) Increases shear capacity of member, 3-) Increases moment capacity, 4-) Increases ductility, 5-) Increases bond of reinforcement, 6-) Improves crack control, 7-) Improves control of spalling, 8-) Increases impact resistance of the regular lightweight concrete member. In addition, material properties of fibre reinforced concrete are influenced to a large extent by the type, volume percentage, aspect ratio, nature of deformation, and orientation of the fibres. Several studies have shown that steel fibres can act compositely in normal concrete structural members. Many works have been done about these normal concrete with steel fibre. But the use of steel fibre in lightweight and semi- lightweight concrete investigations are not enough. Because of wide resources of natural pumice lightweight aggregate in Turkey and useful properties in the lightweight and semi- lightweight concrete members, we have to give important in these works. In addition for structural applications of lightweight concrete, the density of concrete is often more important than strength. If we decrease density for same strength XIlevel permits a savings in dead load for structural design, we can obtain good results and get economic solution. The last physical properties may be improved by the introduction of fibres in to the concrete. The present work has been undertaken for this purpose. It consist of five parts. In the first part, an introduction is given containing the objective of the investigation, relevant general informations, about lightweight aggregates, semi-lightweight concretes, and fibres, main idea about present work. The second part is devoted to the experimental studies. The materials used, the principles assumed, the mix compositions, the methods of mixing and curing, the types of loading, the equipment and the methods employed in the testing and measurements made are described. In the third part, the experimental result are presented. The experimental results are discussed and evaluated in the fourth part. In the fifth part the conclusions are summarized. In the present work, the maximum particle size and grading of the aggregate, the cement content and effective water /cement ratio of the concrete were kept constant. For a selected unit weight level of the concrete, the lightweight and semi-lightweight concrete series were used in this work. Lightweight and semi-lightweight concretes were produced using five different percentage of the steel fibre. All of concrete series as follows : 1- Normal concrete 2- Semi-lightweight concrete (no fibre) 3- Lightweight concrete (no fibre) 4- Semi- lightweight concrete (0.5 % of fibre by volume) 5- Semi- lightweight concrete (0.8 % of fibre by volume) 6- Semi- lightweight concrete (1.2 % of fibre by volume) 7- Semi- lightweight concrete (1.5 % of fibre by volume) 8- Lightweight concrete (0.5 % of fibre by volume) 9- Lightweight concrete (0.8 % of fibre by volume) 10- Lightweight concrete (1.2 % of fibre by volume) 11- Lightweight concrete (15 % of fibre by volume) XIIThe density of semi-lightweight and lightweight concretes were decreased using natural lightweight aggregate instead of normal coarse aggregate. Lightweight aggregates were kept constant volume both semi-lightweight and lightweight concrete series. The above mentioned assumptions 5 standard cylinders (15 x 30 cm) and 3 prism (10 x 10 x 50 cm) were cast from each mix. They were cured for 74 days in water. Two of cylinders under standard Brazilian test and three of them under noncyclic uniaxial compressive loading were tested. Three of prism were tested under four point bending test. The stress-strain curves were recorded until the failure of the specimens, using an x-y recorder. Before the hardened concrete tests, all of the specimens unit weight, pulse velocity tests were applied. The conclusions reached in this work can be summarized in the following groups : The use of the steel fibre in the semi-lightweight and lightweight concretes effect their workability. The increase of the steel fibre content has negative effect on the concrete workability. The use of the steel fibre in the semi-lightweight and lightweight concretes increases air content of these concretes. The use of the steel fibre 1.5 %, in semi-lightweight and lightweight concretes, their compressive strength increase 16 % and 23 respectively. The use of the steel fibre in these concretes, increases strain at the their compressive strength. The use of the steel fibre in the semi-lightweight and lightweight concretes, doesn't change the Young Modulus of the semi-lightweight concrete, but decrease for the lightweight concrete in little. The use of the steel fibre in these concrete, increases the critical stress before ultimate compressive strength. The use of the steel fibre in the semi-lightweight and lightweight concretes, increases their toughness (strain energy). This increasing is 50 % - 67 % for semi-lightweight concrete, 340 % for lightweight concretes. The use of the steel fibre 1.5 %, increases standard Brazilian test strength, % 175-170 and 300 % -265 % for semi-lightweight and lightweight concretes respectively. XHIThe use of the steel fibre, doesn't change their pulse velocity. The increase of the steel fibre content in these concretes, increase the unit weight of these concrete. The use of the steel fibre can reach the strength of the normal concrete strength. Due to decreasing dead load, we can find economic result at the structural members area. XIV

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