Carbon Fiber Reinforced Polymer (CFRP) composites with fibers/fabrics bonded with organic polymers (resin system) are being referred to as the materials of 21st century because of many inherent advantages including market acceptance. The application of composites in civil infrastructure projects started in late 1980, with major advances in bridges, roads, retrofitting of structures, and marine applications. In the last decade, significant efforts have been made to develop design guidelines, and construction and maintenance standards, and specifications for FRP reinforcement, CFRP being one of them, FRP wraps, and FRP shapes including standardized test methods.. Strengthening with externally bonded CFRP fabric has shown to be applicable to many kinds of structures. Currently, this method has been applied to strengthen such structures as column, beams, walls, slabs, etc. The use of external CFRP reinforcement may be classified as flexural strengthening, improving the ductility of compression members, and shear strengthening. It is well known that reinforced concrete beams strengthened with externally bonded fiber-reinforced polymer (FRP) or CFRP to the tension face can exhibit ultimate flexural strength greater than their original flexural strength. However, these FRP and CFRP strengthened beams could lose some of their ductility due to the brittleness of FRP and CFRP plates. The high strength-to-weight ratio, resistance to electrochemical corrosion, larger creep strain, good fatigue strength, potential for decreased installation costs and repairs due to lower weight in comparison with steel, and nonmagnetic and non-metallic properties of fiber reinforced polymer (FRP) composites offer a viable alternative to bonding of steel plates. The emergence of high strength epoxies has also enhanced the feasibility of using CFRP sheets and carbon fiber fabric for repair and rehabilitation. In the experimental study conducted, there point Flexural testing method was used comprising of 6 samples of beams, the details of which are as follows;  2 control beams-CB(kept as the reference)  2 Un-cracked beam retrofitted with CFRP-CFB  2 Pre-cracked beam retrofitted with CFRP-RFB The various findings of the experiments are summarized as under;  The ultimate load-carrying capacity of the strengthened (CFB and RFB) beams was increased as compared to the control beams (CB).  CFRP sheets increased the strength and stiffness of the beams to a great extent with eventual de-bonding failure at the ultimate load.  Beams strengthened with CFRP sheets showed lesser deflections as compared to the control beams (CB).  The crack widths were decreased substantially in the strengthened beams as compared to those in the control beams, with a significant increment in the moment capacity of he strengthened beams.  The Pre-cracked (RFB) and Un-cracked (CFB) strengthened beams exhibited similar deflection characteristics. But pre-cracked beam showed about 60% more deflection than un-cracked beams at service load of the control beams (CB), but later on both showed similar behavior. Additional work and elaboration on various under-addressed aspects is necessary as discussed in the summary and recommendation section of this thesis, to exploit the profound and widespread benefits of CFRP composites in making the structures more economical, having longer service lives and exhibiting better performance with lower maintenance requirements.

Abstract

Carbon Fiber Reinforced Polymer (CFRP) composites with fibers/fabrics bonded with organic polymers (resin system) are being referred to as the materials of 21st century because of many inherent advantages including market acceptance. The application of composites in civil infrastructure projects started in late 1980, with major advances in bridges, roads, retrofitting of structures, and marine applications. In the last decade, significant efforts have been made to develop design guidelines, and construction and maintenance standards, and specifications for FRP reinforcement, CFRP being one of them, FRP wraps, and FRP shapes including standardized test methods.. Strengthening with externally bonded CFRP fabric has shown to be applicable to many kinds of structures. Currently, this method has been applied to strengthen such structures as column, beams, walls, slabs, etc. The use of external CFRP reinforcement may be classified as flexural strengthening, improving the ductility of compression members, and shear strengthening. It is well known that reinforced concrete beams strengthened with externally bonded fiber-reinforced polymer (FRP) or CFRP to the tension face can exhibit ultimate flexural strength greater than their original flexural strength. However, these FRP and CFRP strengthened beams could lose some of their ductility due to the brittleness of FRP and CFRP plates. The high strength-to-weight ratio, resistance to electrochemical corrosion, larger creep strain, good fatigue strength, potential for decreased installation costs and repairs due to lower weight in comparison with steel, and nonmagnetic and non-metallic properties of fiber reinforced polymer (FRP) composites offer a viable alternative to bonding of steel plates. The emergence of high strength epoxies has also enhanced the feasibility of using CFRP sheets and carbon fiber fabric for repair and rehabilitation. In the experimental study conducted, there point Flexural testing method was used comprising of 6 samples of beams, the details of which are as follows;  2 control beams-CB(kept as the reference)  2 Un-cracked beam retrofitted with CFRP-CFB  2 Pre-cracked beam retrofitted with CFRP-RFB The various findings of the experiments are summarized as under;  The ultimate load-carrying capacity of the strengthened (CFB and RFB) beams was increased as compared to the control beams (CB).  CFRP sheets increased the strength and stiffness of the beams to a great extent with eventual de-bonding failure at the ultimate load.  Beams strengthened with CFRP sheets showed lesser deflections as compared to the control beams (CB).  The crack widths were decreased substantially in the strengthened beams as compared to those in the control beams, with a significant increment in the moment capacity of he strengthened beams.  The Pre-cracked (RFB) and Un-cracked (CFB) strengthened beams exhibited similar deflection characteristics. But pre-cracked beam showed about 60% more deflection than un-cracked beams at service load of the control beams (CB), but later on both showed similar behavior. Additional work and elaboration on various under-addressed aspects is necessary as discussed in the summary and recommendation section of this thesis, to exploit the profound and widespread benefits of CFRP composites in making the structures more economical, having longer service lives and exhibiting better performance with lower maintenance requirements.