This study experimentally examined the effect of nanomaterial on the tensile behavior of carbon fiber-reinforced polymer (CFRP) composites. Multiwalled carbon nanotubes (MWCNT), graphene nanoplatelets (GnPs), and short multiwalled carbon nanotubes functionalized COOH (S-MWCNT-COOH) with 1% by weight were used as the primary test parameters. In the present test, S-MWCNT-COOH was more effective than the others in improving the maximum tensile strength, ultimate strain, and toughness of the CFRP composites. The use of S-MWCNT-COOH increased the maximum tensile strength, ultimate strain, and toughness of the CFRP composites by 20.7, 45.7, and 73.8%, respectively. In addition, tensile tests were carried out for CFRP composites with S-MWCNT-COOH after subjection to elevated temperatures ranging from 50 to 200°C. The test results showed that the tensile strength, ultimate strain, and toughness were significantly reduced with increasing temperature. At a temperature level of 100°C, the reduction of the maximum tensile strength, ultimate strain, and toughness was 36.5, 37.1, and 60.0%, respectively. However, for the specimens subjected to the elevated temperatures ranging from 100 to 200°C, the tensile behavioral properties were constantly maintained. Finally, various analytical models were applied to predict the tensile strength of the CFRP composites with S-MWCNT-COOH. By using the calibrated parameters, the tensile strengths predicted by the models showed good agreement with the experimental results.
The tensile behaviors of textile-reinforced mortar (TRM) composites made with carbon fiber textile and alumina cement-based mortar were investigated through direct tensile tests. Three different surface treatment details in the lap splice area were used to improve the tensile behaviors of the TRM composites: carbon fiber textile impregnated by epoxy, carbon fiber textile coated with aluminum oxide powder following epoxy impregnation, and carbon fiber textile coated with aluminum oxide powder following both carbon fiber fabric attachment and epoxy impregnation. Three different lap splice lengths were used 180, 200, and 220 mm. In addition, the tensile properties of TRM composites following exposure to high temperature were investigated as well. In this test, TRM test specimens were exposed to two different temperature histories with maximum values of 250 and 350 °C. The results of the test specimens according to the test parameters were analyzed in terms of initial stiffness, cracking strength, corresponding strain at cracking, modulus of elasticity in the cracked stage, peak strength, and ultimate strain. The influence of lap splice length on the tensile behaviors of the TRM composites was analyzed and discussed. The surface treatment in the overlapping region showed ductile behavior and resulted in a significant improvement of the peak strength and ultimate strain over the untreated lap splice textile. Following exposure to high temperature, the TRM composites showed a reduction of tensile responses compared to those cured at room temperature. In addition, a prediction model developed in the previous study was used to predict the tensile behaviors of the lap-spliced carbon fiber-textile reinforced mortar composites exposed to high temperature, and the prediction by the model showed a good agreement with the experimental results.
Beam-column joints in existing concrete buildings might not satisfy the design requirements for seismic reinforcement details specified in current seismic design codes. Thus, in this study, various retrofit solutions for existing exterior beam-column joints with non-seismic details were developed: head re-bars anchoring, carbon fiber reinforced polymer (CFRP) wrapping, haunch retrofit element, and steel jacketing with various shapes and sizes. To investigate the seismic performance of exterior joints strengthened with the proposed retrofit solutions, seven half-scale exterior reinforced concrete beam-column joints including one control specimen and six retrofitted specimens were fabricated and tested under cyclic loading simulating earthquake loading. The test results showed that the proposed retrofit solutions could partially enhance the seismic capacity of the beam-column joints: steel jackets could increase deformation and load-carrying capacities; steel haunch elements could increase the load-carrying capacity, stiffness, and dissipated energy; and head re-bar anchoring and CFRP wrapping did not significantly effect on the seismic capacity of the beam-column joints.
In the present study, tensile tests were carried out to investigate the tensile behaviors of textile reinforced mortar (TRM) composite specimens. The TRM specimens were composed of one layer of carbon fibers, as the reinforcement, and aluminum cement-based mortar, as the matrix. The primary parameter of the test specimens was the anchorage method, which was newly developed to improve the tensile behavior of the composite: spreading the ends of fiber filaments, reinforcing the ends of fiber filaments using glass fiber reinforced polymer tabs or steel rebars, and coating the ends of fiber filaments with aluminum oxide powder. From the test results, it was found that most TRM specimens using developed anchorage methods exhibited ductile behavior. Moreover, the use of the developed anchorage methods could increase the cracking strength and peak strength of the composite specimens up to 66.1 and 97.9%, respectively. The failure mode of the test specimens was governed by a partial rupture of carbon fibers, except for the BASE specimen and specimen reinforced with steel rebars. Finally, the tensile stress-strain relationship of TRM specimens was idealized as bilinear stress-strain response curves following the guidance specified in ACI 549.4R-13.
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