Deformed rebar

Keywords pitch-based high performance-type carbon continuous fiber reinforced plasUc, chemically resolvable resin, environment-conscious materials (ecomaterials) design, deformed rebar, hybrid structure, lighweight precast concrete, recycle, service life,... 

Various efforts have been made to estimate the amount of corrosion that will cause spalling. It has been shown that cracking is induced by less than 0.1 mm of steel section loss, but in some cases far less that 0.1 mm have been needed. This is a function of the way that the oxide is distributed (i.e. how efficiently it stresses the concrete), the ability of the concrete to accommodate the stress (by creep, plastic or elastic deformation) and the geometry of rebar distribution that may encourage crack propagation by concentrating, stresses, etc., for example, in a closely spaced series of bars near the surface, or at a corner where there is less confinement of the concrete to restrain cracking. 

Even with good initial adhesion there was a loss of adhesion for concrete specimens exposed to regular or continuous wetting. Adhesion testing on the deformed surface of a rebar is difficult to perform quantitatively and there is some disagreement over whether the loss of adhesion when wet is permanent, fully or partially recovered if the bar dries out. Even if it is temporary, the bar is more susceptible to corrosion and under-film attack at defects while wet and once corrosion has started it will not recover adhesion. 

Even ivith good initial adhesion there was a Loss of adhesion for concrete. specimens exposed to regular or continuous wetting. Adhesion testing on the deformed surface of a rebar is difficult to perform... 

Real-time measurement of the structural response was achieved by using an electronic data acquisition system. Several instruments were used to monitor the specimen behavior linear variable displacement transducers (LVDTs) to monitor the global deformed shape and the joint panel shear strain a potentiometer on tip beam to monitor the actual displacement imposed by the actuator to the specimen strain gauges on internal steel rebars to record their strains at ends of beam and columns and strain gauges on CFRP quadriaxial sheet along fibre directions to monitor FRP strains at joint panel. 

Rebars are polymer fibre reinforced-concrete composites, and they are used as primary structures. It is estimated that replacement of steel reinforcing bars by non-corrosive polymer fibres, i.e., by Kevlar or carbon fibres (which gives rise to Kevlar or C-composite bars) for concrete structures produces structures with one-quarter the weight and twice the tensile strength of the steel bar. It is known that, corrosion of steel reinforcement from carbonation or chloride attack can lead to loss of the structural integrity of concrete structures, and such a danger is non-existent for rebars. Thermal expansion coefficient (TEC) values of these fibres are closer to concrete than that of steel, which provides an another advantage and they have the same surface deformation patterns as the steel bars. In addition, they can provide more economy than epoxy-coated steel bars. 

To determine the effectiveness of the proposed retrofitting technique using NSM BFRP rebars (with different textures), the apparent damage, residual deformations, and the force-displacement curves were compared for the three test models. 

Fahmy, M.F.M., and Wu, Z.S. (2012). Seismic performance of RC bridge columns retrofitted with smooth and deformed near-surface-mounted basalt FRP rebars . 6th Int. Conf. on FRP Composites in Civil Engineering (CICE 2012), Rome. 

Fahmy, M.F.M., Wu, Z.S., Wu, G., and Sun, Z.Y. (2010b). Post-yield stiffnesses and residual deformations of RC bridge columns reinforced with ordinary rebars and steel fiber composite bars . Journal of Engineering Structures, 32 2969-2983. 

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