Silis dumanı içeren yüksek mukavemetli betonların enerji tutma kapasitelerinin artırılmasında çelik lif kullanımının etkisi
Başlık çevirisi mevcut değil.
- Tez No: 55490
- Danışmanlar: PROF.DR. SAİM AKYÜZ
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 75
Özet
ÖZET Sunulan bu çalışmada, silis dumanı içeren yüksek performanslı betonlarda enerji tutma kapasitesinin artırırmasında çelik lif kullanılmasının etkisi araştırırdı. Araştırma iki aşamadan oluşmaktadır. Birinci bölümde;silis dumanı içermeyen yüksek performanslı betonlarda dört değişik tipteki çelik lifin işlenebilirlik ve enerji tutma kapasitesindeki etkileri incelendi. Bu bölümde seçilen iki tip çelik lif ile araştırmaya devam edildi. İkinci bölümde ise; silis dumanı içermeyen ve çimento dozajına nispeten ağırlıkça %10 ila %20 oranlarında silis dumanı içeren yüksek performanslı betonlar üzerinde yapıldı. İlk bölümde seçilen iki tip çelik lif ayrı ayrı ve iki değişik oranda karıştırılarak bu üç cins yüksek performanslı betona katıldı. Bu betonların basınç dayanımı, eğilme dayanımı, yarma dayanımı, ultrases hızı, elastisite modülü, gevreklik indisi, süreksizlik sınırı, çözülme sınırı, poısson oranı, kırılma işi ve bağıl kırılma işi değerleri saptandı. Üretilen Betonlarda en büyük agrega boyutu, ganülometri, su/çimento oranı, süperakışkanlaştırıcı /çimento oranı, beton hacmine göre çelik lif oranı sabit tutulup silis dumanı/çimento oranı değiştirirdi. İşlenebilirliğin sağlanması için 4, birinci bölümde 5, ikinci bölümde 15 karışım üretildi. İlk 9 karışımda 28 günlük, ikinci bölümde ise 28 ve 90 günlük numuneler üzerinde eğilme, yarma, ultrases deneyleri yapıldı. Basınç deneylerinde tepe noktası öncesinde yükleme-boşaltma yapılarak betonların elastisite modülü, gevreklik indisi, süreksizlik sınırı, çözülme sınırı, poısson oranı, kırılma işi ve bağıl kırılma işi değerleri saptandı. Deneysel sonuçlara göre silis dumanı ve çelik lif kullanılımı işlenebilirliği olumsuz yönde etkilediği görüldü. Kullanılan çelikli İlerin boyu artıkça veya lif karışımında uzun boylu liflerin oranı artıkça kısa boylu liflere nispeten işlenebilirliğin daha da zorlaştığı saptandı. Silis dumanı ilavesi veya miktarının artırılması da işlenebilirliği zorlaştırdığı görüldü. Silis dumanı ve çelik lif kullanımının betonun basınç eğilme, yarma, süreksizlik sınırı ve çözülme sınırını, kırılma işini artırdığı bulundu. Silis dumanı kullanılmasının gevreklik indisini artırdığı, çelik lif kullanılmasının da azaltığı saptandı. Çelik Lif kullanımının elastisite modülünü azda olsa azalttığı, ultrases hızlarını ise değiştirmediği görüldü. XIİİ
Özet (Çeviri)
SUMMARY STEEL FIBER EFFECT ON THE TOUGHNESS OF HIGH PERFORMANCE CONCRETE CONTAINING SILICA FUME Increasingly, steel fiber reinforced concrete is used in construction, which is defined as concrete in which relatively long and thin steel fibers have been added, typicaly 6 to 60 mm long with a diameter or equivalent diameter of 0. 1 5 to 1 mm. The stresses occurring in a concrete are complex and depending on the type of load, tensile stresses can form both at the top and at the bottom of the concrete cross section. In addition, there are stresses wich are difficult to quantify, wich arise from a number of causes including sharp turns by fork-lift trucks, shrinkage and thermal effect, impact loads, and so on. Steel fibres form an ideal reinforcement for industrial floor slabs on grade, and they effectively limit the extension of microcracks always present in concrete. In concrete without fibres, tension cannot be transmitted across the crack. In plain concrete, once the tensile capasity is exceeded, the micro-cracks will extend rapidly resulting in brittle failure. Steel fibres control the cracking mechanism. The concentration of stresses near the micro-cracks is reduced by: i) Fibres that bridge the crack and transmit some of the load across the crack. ii) Fibres near the crack tip that resist more load because of their higer moduli of elasticity compered to the surrounding concrete. The failure behaviour of concrete is thus altered. It concerns a ductile failure instead of a brittle faillure. A crack is formed where the ultimate stresses in the concrete is locally exceeded. This crack behaves as a hinge due to the steel fibres, resulting in a redistribution of stresses. Unlike a broken zone in a brittle material, this hinge can still resist certain stresses ( depending on the type of fibre used and their amount ) and thus increase the loadbearing capacity of the concrete. The steel fibre reinforce concrete can absorb a great deal more energy than plain concrete. The resistance to impact and fatigue type loading is increased. Breaking or premature deformation of the fibres is prevented by the very high tensile strength of the drawn wire ( greater than 1100 N/mm2 ). Steel fibres distributed uniformly reinforce the concrete in all directions, both at the top and at the bottom. xivThe difference between various types of steel fibres and their effect on concrete is not always clearly understood. Under the motto of“all steel fibers are alike”, the design specifications are then limited to an amount of steel fibers only, irrespective of the type of fiber. This method can have serious consequences, resulting in selection of the cheapest fibers while disregarding the final performance of the fiber in the concrete. The market will evolve towards cheaper fiber without worrying about the performance of steel fiber reinforced concrete. If we look at reinforcement with steel bars, we see a product that is standardised. A certain quality of steel bar is specified and all strength calculations are based on that quality. The resulting amount of steel bar reinforcement is therfore based on standards of steel strength and quality and is clearly specified for all users. The same principle should be followed in steel fibers. Again, only specifying a dosage rate of steel fibers means the quality of the different steel fibers is not taken into account, which can be extremely dangerous. Toughness gives the steel fiber concrete characteristics which are comparable to reinforced concrete. Even after cracking the steel fiber concrete retains a certain load bearing capacity, which can be higher or lower than the capasity at first crack. This is dependent on the type of construction ( the degree of hyperstaticity ) and the type and dosage rate of fibers. Structures in steel fiber concrete must be calculated based on these toughness characteristics. In summary, we can say that steel fiber concrete has a real tensile or flexural strength, even after cracking. Silicafume is a by-product of the silicon ( or metal-silicon alloys ) industry. In high temperature arc furnaces escaping silicon monoxide gas (SiO) is oxidized to silicon dioxide (Si02) and condenses, forming glassy spherical particles. This condensed silica fume has an average particle size about 1 00 times smaller than a grain of type I Portland cement. This is about the size of the particles in smoke. Because of the submicron size of these silica particles, they are also called microsilica. Microsilica, because of its high Si02 content and fine particle size, is an extremely reactive pozzolan for portland cement concretes. The basic concept of the pozzolanic reaction can be explained in simple terms. Portland cement and water react to poroduce calcium silicate hydrates, the“glue”which binds the concrete material together and calsium hydroxide. Calsium hydroxide does not contribute as a binder but remains as a defect in the glue. When microsilica is added to the system, calcium hydroxide combines with the glassy silicon dioxide and water to form additional calcium silicate hydrates as illustrated below: Cement + H20 > Calcium Silicate Hidrates + CaCOH^ Ca(OH2) + Si02 + H20 > Calcium Silicate Hidrates This additional“binding”increases the compressive, flexural and tensile strength of the concrete. In addition, by virtue of its particle size, microsilica is a very efficient filler in the concrete system, filling voids between cement grains and aggregates, while XValtering the pore structure of the system. The result is a stronger, dramatically less permeable concrete. The main object of this study was to investigate the influance of steel fiber effect on the toughness of high performance concrete containing silica fume. The influence of fiber type on the performance of steel fiber reinforced concrete were also investigated. This is the result of an experimental study on the relative effectiveness of different types of steel fiber and of microsilica in concrete. The fibers considered in this study were ZC 60/0.80, ZC 50/0.50, ZC 30/0.30 and ZC 6/0.15. A constant fiber volume fraction of 0.9 percent was used throughout this investigation. The fresh mixes were characterized by their slump, inverted slump-cone time as workability, and the hardened material by their compressive, flexural, and splitting strengths and load-deformation relationships. The concretes produced in this study are as follows: i) Four different water/cement and superplasticizer/cement ratios such as %30+%1.8(Dl), %35+%3.0 (D2), %30+%2.5 (D3), %35+%2.5 (D4) ii) Four different steel fiber types such as ZC 60/0.80 (ÖI), ZC 50/0.50 (Oil), ZC 30/0.50 (ÖIII) and ZC 6/0.15 (ÖIV). iii) Two different silica fume volumes such as % 1 0 (A,j), %20 (A2J) iv) Two fiber types and mixing of two different fiber types such as [0.009 X ZC 6/0.15] (Ah), [0.009 X ZC 30/0.50] (Al2), [0.0045 X ZC 6/0.15 + 0.0045 X ZC 30/0.50](A,3) and [0.003 X ZC 6/0.15 + 0.006 X ZC 30/0.50](Al4). v) Three reference concretes without fiber such as \0, \x, Aq2. Water/cement ratio, superplasticizer/cement ratio, fiber ratio and the maximum particle size for all concrete series have been kept constant. The water/cement ratio, superplasticizer/cement ratio and the maximum size of aggregate were 0.35, 0.025 and 160 mm, respectively. Mechanical tests were carried out on the standart cylenderical (15X30 cm) and standart prismatical (10X10X50 cm) specimens. They were cured for 28 and 90 days in water. Test results obtained are evaluated in terms of following properties: Fresh concrete properties, elastic and inelastic properties, compressi strength, splitting tensile strength, flexural capacity, ultrasonic pulse velocity, the brittleness index and modulus of elasticity. After 28 days, three of the cyclinders under by using the standart Brazilian split cylinder test technique and three of them were tested under noncyclic uniaxial compressive loading. Four of prisms were tested under four point bending. After 90 days, one of cylinder under the standart Brazilian split test and one cylinder under xvinoncyclic uniaxial compressive loading were tested. Two of the prisms were tested under four point bending test. Before the Brazilian and flexural tests, ultrasonic pulse velocity testes were applied to the specimens. The conclussion reached in this study can be summarized in the following groups. 1. The Results Related to the Workability: i) The use of the steel fiber and the silica fume in the concretes effect their workability. The increase of the steel fiber content has negative effect on the concrete workability. ZC 60/0.80 and ZC50/0.50 are worse than ZC 30/0.50 and ZC 6/0. 15.ZC 50/0.50 is the worst fiber, while ZC 6/0. 15 is found as the best fiber. ii) The use of the steel fiber increases air content of concretes. iii) The use of the silica fume decreases air content of concrete. 2. The Results Related to the Elastic Behavioure: i) Silica fume and steel fiber effect the modulus of elasticity, such that, silica fume increases it while stell fiber decreases it. The modulus of elasticity increases by time. ii) İn concrete produced without silica fume, poisson ratio has a minimum value around a steel fibre concentration of 0.260 m3/m3. When silica fume is introduced the poisson ratio shows a minimum around a concentrastion 0.272 m3/m3. 3. The Results Related to the Inelastic Behavioure: i) The use of steel fiber and silica fume in concretes increase the strain at compressive strength. ii) The use of the steel fiber in concretes, increased the critical stress before ultimate compressive strength. 4. The Results Related to the Toughness: i) The use of the silica fume in the concretes increase the toughness. The increases are %38-65 at the age of 28 days, and % 18-49 at the age of 90 days. ii) The use of the steel fiber in concretes also increases their toughness. Thes increases are %50 at age of 28 days, and %38 at the age of 90 days. iii) The use of both the steel fiber and the silica fume in the concretes, increases their toughness and the increases are %102 at the age of 28 days, %188 at the age of 90 days. xviiiv) Toughness dependent on the fiber type. 5. The Experimental Results Related to the Flexural and the Splitting Tensile Strength: i) The use of steel fiber or silica fume increases both flexural and standart brazilian split cylinder test strength. ii) The use of steel fiber and silica fume very increases at the same time at the same mix these strengths in large amounts comparing to those of concretes in which the ingredients used alone. iii) The effect of time on the results is slight. 7. The Results Related to the Ultrasonic Pulse Velocity: i) The inclusion of the steel fiber in concrete does not change the ultrasonic pulse velocity. ii) The use of the silica ftime increases the pulse velocity with respect to plain concrera. iii) To effect of time on pulse velocity is slight. 8.The Results Related to the Britllcness of Concretes Under Uniaxial Compression tests: i) The increas of the silica fume content in the concretes increases the brittleness ii) The use of the steel fiber in the concrete decreases it iii) Combined use of steel fiber and silica fume in the concretes increases the brittleness. xviii
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