Farklı Tipteki Poliolefin Liflerin Betonun Mekanik Özelliklerine Etkisi
Farklı Tipteki Poliolefin Liflerin Betonun Mekanik Özelliklerine Etkisi
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Tarih
2014-02-14
Yazarlar
Yorulmaz, Burak
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Institute of Science and Technology
Institute of Science and Technology
Özet
Gevrek bir yapı malzemesi olan betona lif ilave edilmesiyle daha sünek bir yapı oluşturularak betonun bazı mekanik özelliklerinde iyileşme beklenir. Lifler; tipi, boyutu, geometrisi, miktarı, çekme dayanımı ve yüzey özellikleri gibi birçok parametreye bağlı olarak betonda dayanımı, çatlak kontrolünü, şekil değiştirme kapasitesini, enerji yutma kapasitesini ve durabiliteyi arttırır. Betonda kullanılan lifler kullanım amacına göre birçok farklı çeşit lif türü bulunmaktadır. Beton gevrek yapısı nedeniyle ilk çatlakla beraber kırılma mekanizmasını tamamlar. Betona lif eklenmesi durumunda kırılma mekanizması ilk çatlak ile başlar. Çatlağın betonda ilerlemesini sağlayan gerilme enerjisi, çatlak life ulaştığında lif üzerine aktarılır. Lif bu enerjiyi sıyrılana kadar ya da kopana kadar taşır sonrasında tekrar betona aktarır. Betonun çatlamaya devam etmesiyle bu mekanizma nihai çatlak oluşuncaya kadar devam eder.Kırılma mekanizması tamamlandığında betonda parallel çatlaklar oluşur. Böylelikle, lifin betona eklenmesi gervek bir malzeme olan betona sünek özellik kazandıracaktır. Bu çalışmada kısa ve uzun geometrilerdeki poliolefin liflerin farklı oranlarda kullanılmasının betonun mekanik özelliklerine etkisi incelenmiştir. Çalışma kapsamında kompozit malzemenin mekanik özelliklerini irdeleyen basınç ve eğilme deneyleri yapılmıştır. Ayrıca elektron mikroskobu ile mikro yapı incelemesi gerçekleştirilmiştir. Mikro yapı incelemesinde üç noktalı eğilme deneyi uygulanmış numune üzerindeki kırılma yüzeyinden elde edilen numuneler üzerinde gerçekleştirilmiştir. Görüntülemede lif yüzeyleri, lif uç bölgeleri ve lif matris birleşimi incelenmiştir. Bu çalışmayla lifin yük etkisi altındaki davranışı ve matris ile lif arasındaki aderans incelenmiştir. Deneysel çalışmalar neticesinde kullanılan kısa liflerin, matrisin basınç dayanımını artırdığı sonucuna ulaşılmıştır. Ancak matrise uzun lif eklenmesinin, matriste basınç dayanımını düşürdüğü belirlenmiştir. Basınç dayanımınındaki bu azalamanın uzun liflerin beton içerisinde boşluk gibi davranmasından kaynaklandığı düşünülmektedir. Karışımlara uygulanan üç noktalı eğilme deneyi sonuçlarına göre liflerin matrisin enerji yutma kapasitesinde artışa neden olduğu belirlenmiştir. Bu artışta uzun liflerin, kısa liflere nazaran daha etkili olduğu görülmüştür. Liflerin hacime %1 oranında kullanılmasının matrisin eğilme dayanımını düşürdüğü belirlenmiştir. Bunun sebebinin, betonda çatlağın ilerlemesine neden olan gerilme enerjisinin aktarılması için yeterli miktarda lifin matris içerisinde bulunmaması olduğu düşünülmektedir. Uzun ve kısa liflerin mikro yapıları incelendiğinde, uzun liflerin yüzey pürüzlülüğünün kısa liflere göre fazladır. Ayrıca uzun liflerin uç kısımlarının düzenli fibrile yapıda olması matrise tutunmayı artırmıştır. Bu durum uzun liflerin mekanik özelliklerinin kısa liflere göre daha yüksek olmasını açıklamaktadır.
In recent years, there is an increasing interest of using cement based composites with synthetic fiber additives due to its superior properties compared to conventional concrete. Fiber additives make it possible to produce high durability cement based composites and thin wall cement based materials which can not be produced with conventional steel reinforcement concrete. due to its superior properties Fiber reinforcement concretes has a wide using area such like road concretes, industrial flooring, hydro buildings, tunnels, bridges, blast proof military buildings, runways of airports, concrete pipes and pre-cast concrete materials. The mechanical properties of concrete is expected to convert from a ductile structural material to much more ductile structural material while adding the fiber to the concrete. The parameters as strength, cracking control, the capacity of deformation, energy holding capacity, and durability are all increased due to the type, dimension, geometry, quantity, tensile strength, and surface characteristics of the concrete. There are different fiber types depending on their various intended use on the concrete. The breakage mechanism is completed while the first crack is occurred because of the ductile structure of concrete. In the case of adding the fiber into the concrete material, the first crack is initiated the breakage mechanism. The strain energy that makes the crack possible to move on the concrete material is directed onto fiber while the crack is reached to the fiber. The fiber bears the strain energy as much as it can endure and the energy is transferred back to the concrete. This process is repeated during the load increases with existing many parallel cracks on the element. The attached fiber makes the concrete much more ductile compared to the original ductile nature of the concrete material. Thinner, lighter and cost saving materials can be produced with higher durability. Fiber additives increase the tensile strength which results into less shrinkage cracks during hardening and hydration and an increasing in fatigue performance, strength and durability. There are various types of fibers used as an additive in cement based materials. High strength fibers like Glass, carbon, aramid and high density polyetilene increase the composites strength and toughness and stiffness when added. Low modulus fiber additives like polypropylene and polyethylene increases the ductility. However this kind of fibers have a limited effect on increasing strength of concrete In this study, short polyolefin fibers with different geometric features were used to observe the effect of mechanical properties of the concrete depending on different ratio of polyolefin fibers. In the scope of this study, compressive and bending test are conducted to obtain the mechanical properties of composite material. Microstructure investigation of Failure surfaces of Three point bending test applied samples is performed with scanning electron microscopy (SEM). Fiber surfaces, fiber tail ends and fiber-matrix conjunctions are inspected in detail by SEM. Fibers behaviors were investigated under load and adherence between fiber and matrix are observed. On the basis of experimental results, it is observed that short polyolefin fibers increase the pressure strength of the matrix. However, the pressure strength of the matrix decreases due to the addition of long fibers. The reason behind the decrement of pressure strength is the cavitation tendency of long fibers in the concrete. Three point bending test applied to the samples shows that the fibers increase the energy absorbance of matrix. POU fibers are found to be more effective to increase the energy absorbance then POK fibers. The bending strength of matrix decreases depending on the fiber volume of %1. Hence, the quantity of fiber in the matrix is not well enough to direct the strain energy that let the crack to move on the concrete material. The studies showed that using of fibers within the concrete increases the plastic deformation performance. Crack mouths opening displacement is 2mm in control sample, whereas the fiber mixtures is above 3,5 mm. Difference between these values clearly shows the effect of fibers on composite which resulted in increase of ductility. Hence the increase in energy absorbance of the composite due to fiber addition is explained. Long fiber additives have more increasing effect on energy absorbance than short fibers. Beside fiber type energy absorbance is also affected by the amount of additive, more fiber addition results in more increase in energy absorbance indeed. The effect of fiber amount is more remarkable by long fibers. According to Stress-Strain graphs, fiber addition has no significant effect on bending strength. It is an expected result when low elasticity modulus polymere fibers are considered. However, when the added fiber amount is 1%, bending strentgh is decreased. The reason of the decrease is thought to be that fibers do not take enough place within the matrix to affect composites mechanical properties The electron microscopy images show that long fibers physical properties are more effective on increasing the adherence between fiber and matrix. Discrete structure of short fibers contributes to the interphase with matrix. Detachments are seen at the tail ends and surfaces of short fibers. the detachments may be caused of the friction of the aggreagtes during production or tensile forces on fibers during the bending test. Short fibers have less surface roughness and at surface there are less cement paste which affects the adherence. This explains why the short polyolephine fiber concretes have inferior mechanical properties. Fibrilation at the tail ends of long fibers and the surface roughness of the fiber body takes attention. Through this roughness, adhesion between matrix and fiber is increased. In microstructure images it can be clearly seen that there are cement paste remains on fiber surface. It is thought that long fibers have high mechanical properties due to that physical features. Hence it can be said that this physical properties have also an important effect on long fibers high fracture energy.
In recent years, there is an increasing interest of using cement based composites with synthetic fiber additives due to its superior properties compared to conventional concrete. Fiber additives make it possible to produce high durability cement based composites and thin wall cement based materials which can not be produced with conventional steel reinforcement concrete. due to its superior properties Fiber reinforcement concretes has a wide using area such like road concretes, industrial flooring, hydro buildings, tunnels, bridges, blast proof military buildings, runways of airports, concrete pipes and pre-cast concrete materials. The mechanical properties of concrete is expected to convert from a ductile structural material to much more ductile structural material while adding the fiber to the concrete. The parameters as strength, cracking control, the capacity of deformation, energy holding capacity, and durability are all increased due to the type, dimension, geometry, quantity, tensile strength, and surface characteristics of the concrete. There are different fiber types depending on their various intended use on the concrete. The breakage mechanism is completed while the first crack is occurred because of the ductile structure of concrete. In the case of adding the fiber into the concrete material, the first crack is initiated the breakage mechanism. The strain energy that makes the crack possible to move on the concrete material is directed onto fiber while the crack is reached to the fiber. The fiber bears the strain energy as much as it can endure and the energy is transferred back to the concrete. This process is repeated during the load increases with existing many parallel cracks on the element. The attached fiber makes the concrete much more ductile compared to the original ductile nature of the concrete material. Thinner, lighter and cost saving materials can be produced with higher durability. Fiber additives increase the tensile strength which results into less shrinkage cracks during hardening and hydration and an increasing in fatigue performance, strength and durability. There are various types of fibers used as an additive in cement based materials. High strength fibers like Glass, carbon, aramid and high density polyetilene increase the composites strength and toughness and stiffness when added. Low modulus fiber additives like polypropylene and polyethylene increases the ductility. However this kind of fibers have a limited effect on increasing strength of concrete In this study, short polyolefin fibers with different geometric features were used to observe the effect of mechanical properties of the concrete depending on different ratio of polyolefin fibers. In the scope of this study, compressive and bending test are conducted to obtain the mechanical properties of composite material. Microstructure investigation of Failure surfaces of Three point bending test applied samples is performed with scanning electron microscopy (SEM). Fiber surfaces, fiber tail ends and fiber-matrix conjunctions are inspected in detail by SEM. Fibers behaviors were investigated under load and adherence between fiber and matrix are observed. On the basis of experimental results, it is observed that short polyolefin fibers increase the pressure strength of the matrix. However, the pressure strength of the matrix decreases due to the addition of long fibers. The reason behind the decrement of pressure strength is the cavitation tendency of long fibers in the concrete. Three point bending test applied to the samples shows that the fibers increase the energy absorbance of matrix. POU fibers are found to be more effective to increase the energy absorbance then POK fibers. The bending strength of matrix decreases depending on the fiber volume of %1. Hence, the quantity of fiber in the matrix is not well enough to direct the strain energy that let the crack to move on the concrete material. The studies showed that using of fibers within the concrete increases the plastic deformation performance. Crack mouths opening displacement is 2mm in control sample, whereas the fiber mixtures is above 3,5 mm. Difference between these values clearly shows the effect of fibers on composite which resulted in increase of ductility. Hence the increase in energy absorbance of the composite due to fiber addition is explained. Long fiber additives have more increasing effect on energy absorbance than short fibers. Beside fiber type energy absorbance is also affected by the amount of additive, more fiber addition results in more increase in energy absorbance indeed. The effect of fiber amount is more remarkable by long fibers. According to Stress-Strain graphs, fiber addition has no significant effect on bending strength. It is an expected result when low elasticity modulus polymere fibers are considered. However, when the added fiber amount is 1%, bending strentgh is decreased. The reason of the decrease is thought to be that fibers do not take enough place within the matrix to affect composites mechanical properties The electron microscopy images show that long fibers physical properties are more effective on increasing the adherence between fiber and matrix. Discrete structure of short fibers contributes to the interphase with matrix. Detachments are seen at the tail ends and surfaces of short fibers. the detachments may be caused of the friction of the aggreagtes during production or tensile forces on fibers during the bending test. Short fibers have less surface roughness and at surface there are less cement paste which affects the adherence. This explains why the short polyolephine fiber concretes have inferior mechanical properties. Fibrilation at the tail ends of long fibers and the surface roughness of the fiber body takes attention. Through this roughness, adhesion between matrix and fiber is increased. In microstructure images it can be clearly seen that there are cement paste remains on fiber surface. It is thought that long fibers have high mechanical properties due to that physical features. Hence it can be said that this physical properties have also an important effect on long fibers high fracture energy.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2014
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014
Anahtar kelimeler
beton,
hazır beton,
lif takviyeli beton,
polipropilen,
poliolefin,
fiber reinforce concrete,
polyproplene fiber,
ready mixed concrete