Yüksek mukavemetli betonların kırılma parametreleri
Practure parameters of high strength concretes
- Tez No: 46326
- Danışmanlar: DOÇ.DR. M. ALİ TAŞDEMİR
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Kırılma değeri, Yüksek dayanımlı beton, Fracture degree, High strength concrete
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
EGf Jt Where E:Elasticity Modulus and f: tensile strength of the concrete. A smaller lch implies that the material is more brittle. It was verified that the characteristic length increase as the aggregate size increases. Characteristic length strongly decrease as concrete strength increases. A specific method has been proposed by the RILEM Technical Committee TC-50 to quantify the fracture energy, and recommended values have been included in the last CEB Model Code. At the same time the use of high-strength concretes is continuously increasing, but despite the amount of research that has been performed there are still many areas which need to be studied. Fracture toughness is one of them because questions about the“brittleness”of high-strength concretes usually appear. This paper presents results for the fracture energy of concrete obtained from a wide range of high-strength concretes. The behaviours of notched and unnotched specimens with different water-cement ratios were examined and compared. Relationships between fracture parameters ( fracture energy and brittleness ) and basic strength properties are also presented. The influence of maximum aggregate size and type of loading on fracture mechanics parameters are studied. The effect of microsilica and aggregate size on the strain localization, softening response and brittleness of high strength concretes were investigated by measuring the fracture energy. The energy of fracture increases as concrete strength increases. As the strength increases, concretes have a greater peak load deflection followed by a steeper gradient of the softening branch. The final displacements are similar for concretes with different strength. The final displacement is much lower for mortar than for concrete, and it depends on the type (and size) of aggregate. Based on the fracture tests and microscopic studies at the aggregate matrix interface, it is concluded that in concretes which contain microsilica, the cracks usually travel through the aggregates; the interfacial zone for these concretes becomes stronger and more heterogeneuos, and the fracture occurs in a more brittle manner. However, in concretes without microsilica, the cracks usually develop around the coarse aggregate resulting in an inter-coarse aggregate type of fracture. Brittleness of normal and high strength concretes are the compressive strength, splitting tensile strength, net flexural tensile strength; dynamic modulus and fracture energy of concrete increases while characteristic length of the concrete decreases when water/binder ratio decreases. XIV
Özet (Çeviri)
zone is negligible compared to the specimen size. Accordingly, the test method was recommended by RILEM with a lower limit on the specimen size. For concrete with a maximum aggregate size of 16-32 mm, the required beam depth is 200 mm and the length is 1.2 m. The notch length should be half of the depth of the beam. If the total energy consumed (including the work done by the weight of the beam) is G, the fracture energy is: Gf=Wf/At lig where Alig= area of the ligament. It has been shown that the specimen sizes recommended by RILEM do not always provide size-independent values for Gf. The work-of-fracture of beams with depths ranging from 150 mm to 300 mm was determined. It was shown that Gj- increased with an increase in beam depth, and decreased with an increase in notch depth. Though the method yields size-dependent values, it has widely been used due to its simplicity. Availability of extensive data has led to empirical 'code-type' relations linking fracture energy to conventional design properties. One such equations is provided by the CEB-FIP Model Code: Gj- =xFfcm where xF is a tabulated coefficient that depends on the aggregate size (e.g.,for a maximum aggregate size = 16 mm, xF = 6), fcm means compressive strength of the concrete in MPa, and G^is obtained in N/m. It should be emphasized that Gy-,by itself is not a reliable measure of toughness or ductility, and that using Gy-as the sole fracture parameter could lead to erroneous conclusions. If one were to conclude from the observed increase in G^ the increase in with compressive strength that ductility increases with the increas in compressive strength, this would be wrong. With the use of additional parameters (i.e.characteristic length), the higher brittleness in high strength concrete can be adequately characterized. The failure of plain concrete is generally brittle, but not as brittle as that of glass. This ductility, that concrete possesses can be quantified through fracture mechanics. In this work ductility is taken to be the inverse of brittleness. In almost all of the nonlinear fracture models, the brittleness of the material can be related to parameters that depend on the dimensions or the deformations of the fracture process zone. Hillerborg defined a characteristic length lch that is proportional to the process zone length: XlllEGf Jt Where E:Elasticity Modulus and f: tensile strength of the concrete. A smaller lch implies that the material is more brittle. It was verified that the characteristic length increase as the aggregate size increases. Characteristic length strongly decrease as concrete strength increases. A specific method has been proposed by the RILEM Technical Committee TC-50 to quantify the fracture energy, and recommended values have been included in the last CEB Model Code. At the same time the use of high-strength concretes is continuously increasing, but despite the amount of research that has been performed there are still many areas which need to be studied. Fracture toughness is one of them because questions about the“brittleness”of high-strength concretes usually appear. This paper presents results for the fracture energy of concrete obtained from a wide range of high-strength concretes. The behaviours of notched and unnotched specimens with different water-cement ratios were examined and compared. Relationships between fracture parameters ( fracture energy and brittleness ) and basic strength properties are also presented. The influence of maximum aggregate size and type of loading on fracture mechanics parameters are studied. The effect of microsilica and aggregate size on the strain localization, softening response and brittleness of high strength concretes were investigated by measuring the fracture energy. The energy of fracture increases as concrete strength increases. As the strength increases, concretes have a greater peak load deflection followed by a steeper gradient of the softening branch. The final displacements are similar for concretes with different strength. The final displacement is much lower for mortar than for concrete, and it depends on the type (and size) of aggregate. Based on the fracture tests and microscopic studies at the aggregate matrix interface, it is concluded that in concretes which contain microsilica, the cracks usually travel through the aggregates; the interfacial zone for these concretes becomes stronger and more heterogeneuos, and the fracture occurs in a more brittle manner. However, in concretes without microsilica, the cracks usually develop around the coarse aggregate resulting in an inter-coarse aggregate type of fracture. Brittleness of normal and high strength concretes are the compressive strength, splitting tensile strength, net flexural tensile strength; dynamic modulus and fracture energy of concrete increases while characteristic length of the concrete decreases when water/binder ratio decreases. XIVzone is negligible compared to the specimen size. Accordingly, the test method was recommended by RILEM with a lower limit on the specimen size. For concrete with a maximum aggregate size of 16-32 mm, the required beam depth is 200 mm and the length is 1.2 m. The notch length should be half of the depth of the beam. If the total energy consumed (including the work done by the weight of the beam) is G, the fracture energy is: Gf=Wf/At lig where Alig= area of the ligament. It has been shown that the specimen sizes recommended by RILEM do not always provide size-independent values for Gf. The work-of-fracture of beams with depths ranging from 150 mm to 300 mm was determined. It was shown that Gj- increased with an increase in beam depth, and decreased with an increase in notch depth. Though the method yields size-dependent values, it has widely been used due to its simplicity. Availability of extensive data has led to empirical 'code-type' relations linking fracture energy to conventional design properties. One such equations is provided by the CEB-FIP Model Code: Gj- =xFfcm where xF is a tabulated coefficient that depends on the aggregate size (e.g.,for a maximum aggregate size = 16 mm, xF = 6), fcm means compressive strength of the concrete in MPa, and G^is obtained in N/m. It should be emphasized that Gy-,by itself is not a reliable measure of toughness or ductility, and that using Gy-as the sole fracture parameter could lead to erroneous conclusions. If one were to conclude from the observed increase in G^ the increase in with compressive strength that ductility increases with the increas in compressive strength, this would be wrong. With the use of additional parameters (i.e.characteristic length), the higher brittleness in high strength concrete can be adequately characterized. The failure of plain concrete is generally brittle, but not as brittle as that of glass. This ductility, that concrete possesses can be quantified through fracture mechanics. In this work ductility is taken to be the inverse of brittleness. In almost all of the nonlinear fracture models, the brittleness of the material can be related to parameters that depend on the dimensions or the deformations of the fracture process zone. Hillerborg defined a characteristic length lch that is proportional to the process zone length: XlllEGf Jt Where E:Elasticity Modulus and f: tensile strength of the concrete. A smaller lch implies that the material is more brittle. It was verified that the characteristic length increase as the aggregate size increases. Characteristic length strongly decrease as concrete strength increases. A specific method has been proposed by the RILEM Technical Committee TC-50 to quantify the fracture energy, and recommended values have been included in the last CEB Model Code. At the same time the use of high-strength concretes is continuously increasing, but despite the amount of research that has been performed there are still many areas which need to be studied. Fracture toughness is one of them because questions about the“brittleness”of high-strength concretes usually appear. This paper presents results for the fracture energy of concrete obtained from a wide range of high-strength concretes. The behaviours of notched and unnotched specimens with different water-cement ratios were examined and compared. Relationships between fracture parameters ( fracture energy and brittleness ) and basic strength properties are also presented. The influence of maximum aggregate size and type of loading on fracture mechanics parameters are studied. The effect of microsilica and aggregate size on the strain localization, softening response and brittleness of high strength concretes were investigated by measuring the fracture energy. The energy of fracture increases as concrete strength increases. As the strength increases, concretes have a greater peak load deflection followed by a steeper gradient of the softening branch. The final displacements are similar for concretes with different strength. The final displacement is much lower for mortar than for concrete, and it depends on the type (and size) of aggregate. Based on the fracture tests and microscopic studies at the aggregate matrix interface, it is concluded that in concretes which contain microsilica, the cracks usually travel through the aggregates; the interfacial zone for these concretes becomes stronger and more heterogeneuos, and the fracture occurs in a more brittle manner. However, in concretes without microsilica, the cracks usually develop around the coarse aggregate resulting in an inter-coarse aggregate type of fracture. Brittleness of normal and high strength concretes are the compressive strength, splitting tensile strength, net flexural tensile strength; dynamic modulus and fracture energy of concrete increases while characteristic length of the concrete decreases when water/binder ratio decreases. XIVThis study, relations for an estimate of fracture parameters as given in CEB Model Code as well as their justification are summarized. This new model code for the design of concrete structures includes extensive information on constitutive relations for concrete and reinforcing steel. In this model code relations are also proposed to predict fracture properties of concrete on the basis of fracture mechanics concepts. In particular fracture energy is given as a function of concrete grade, maximum aggregate size and temperature. Another work reported in this thesis was to try to compare the relative values of the long tail in the latter part of the strain softening part of the curves. xv
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