Research On TRC Mechanical Behavior And Flexural Performance Of Concrete Beam Reinforced With TRC

Textile-reinforced concrete (TRC) is a new high performance cementitious composite material consisting of multi-axial textile reinforcement made with advanced textile technology and fine-grained concrete. It has excellent ability of directional strengthening and delaying crack. Due to the wonderful corrosion resistance of fiber materials, the concrete cover is no longer needed as a chemical protection. The thickness of TRC members depends primarily on the necessary value to ensure a proper anchorage of the reinforcement and to avoid splitting failure. These features make TRC be widely used in the thin-walled structure with light weight or the cladding material, the corrosion-resistant components, retrofitting or strengthening the existing structure and treating various forms of cracks in the concrete. However, due to the brittle feature of fiber materials, the TRC structural member has no distinct failure symptom when it arrives at its ultimate load. At the same time, ordinary reinforced concrete (RC) elements have large dead weight and can not efficiently restrict the expansion of the main crack of structures because of the restriction of their special cover thickness. Therefore, in this study, combined with the research about the new method for crack control of concrete structures in the Key Program of the National Natural Science Foundation of China (No.50438010)"Research on the Mechanism of Crack Formation and Propagation in Concrete Structures and Crack Control Method", and based on the investigation on the related materials and mechanical properties of TRC, a new architecture reinforced with a combination of textile and steel bar in this study is proposed. Further, a series of tests and analytical work about this new architecture have been carried and the main contents are summarized as follows.1. Compared with ordinary concrete with similar compressive strength, the Young's modulus of fine grained concrete is lower, and the strain at ultimate load is higher. When the experimentally determined control parameters are used, experimental curves show very good agreement with the calculated curves.2. It also exists a nonlinear fracture process and a steady crack propagation stage before unstable fracture of fine grained concrete, and with the increase in beam depth the unstable toughness does not change, but the initial fracture toughness decreases. After the area under the tail of the load-deflection curve is taken into consideration, the fracture energy of fine grained concrete almost does not have size effect and therefore it may be considered as a material parameter. 3. When the yarn is tensioned alone, its stress-strain relationship is almost linear. Assume that only the textile bears the load after matrix material cracking, thus the stress-strain relationship of the yarn, which is obtained from the curves of the load vs. deformation with uniaxial tensile test of TRC-thin plate specimens, can be reasonably simplified as the bilinear form.4. For the component with the same cover thickness, sticking sand on the surface of the textile, adding the short-cut polypropylene fiber into fine grained concrete and hanging U-shaped hooks upon the textile are helpful to improve its mechanical performance. The cover thickness of 3 mm or so is enough to meet the anchorage requirement of the reinforcement fiber.5. The warp yarns and the surface treatment of the textile have significant influences on the interfacial bond performance between the textile and the fine grained concrete. For the textile covered with fine sand, its splicing length, which is no less than 60mm, can meet the requirement of the stress transfer between yarns. At the same splicing length, the enhancement capacity of the textile using the binding splicing is better than that of the textile using the sticking splicing.6. Based on the bending design theory of RC elements, the flexural calculation theory of fine grained concrete reinforced with epoxy resin-impregnated textile is studied. The results show that before cracking, it can be obtained a well fit between the theoretical curves and the experimental curves regardless of the layers of textiles laid, and after cracking, comparison between the calculated and the experimental results reveals satisfactory agreement.7. A new architecture reinforced with textile-combined steel is proposed in this study. The flexural development process of the proper beam with this new structure is investigated and based on the plane section assumption, analytical equations are derived by using nonlinear analysis theory, including the load-carrying capacity at different stages and moment-curvature relationship and mid-span deflection during the entire loading process. Comparison between the calculated and the experimental results reveals satisfactory agreement and thus verifies the feasibility of the equations.8. Two kinds of limit failure state of flexural beam strengthened with textile-combined steel are presented for different amount of the textile, and for each state, the relation between the textile ratio and the steel reinforcement ratio is derived in this study. Afterward, based on the plane section assumption, the calculation methods for the ultimate bearing capacity of the normal section of this component at three kinds of failure mode are also presented. The experimental results show that the first failure mode is unfavorable to the component and the calculated values of ultimate bearing capacity coincide well with the experimental values. 9. The experimental results of flexural performance of reinforced concrete (RC) beams strengthened with TRC show that sticking sand on the epoxy resin-impregnated textile can make its anti-crack ability better exert and thus the crack-control and reinforcing function of TRC layer can be fully utilized, and embedding U-shaped pins into the old concrete contributes to improve the whole mechanical behavior of RC beams strengthened with TRC, but smearing interfacial agent on the surface of the old concrete has almost no effect on the beams. In addition, mixing polypropylene fiber into fine grained concrete is helpful to enhance the initial cracking load of the component.And when the ratio of steel reinforcement is constant, increasing the ratio of textile reinforcement in TRC can effectively delay the development of main cracks of the structure, and decrease the crack width and the crack spacing and significantly improve the yield load and ultimate bearing capacity of the beams.10. Comparison between the calculated and the experimental load vs. deflection curves of RC beams strengthened with TRC reveals satisfactory agreement. Based on the calculation theory for the crack spacing and width of RC elements, the influences of the textile on the control parameters for the crack calculation of RC structures are qualitatively analyzed.