| Textile Reinforced-Ultra High Performance Concrete(TR-UHPC)can utilize the synergistic effects of short fiber and textiles to further improve the tensile strength,ductility and toughness of UHPC.The workability can be improved with lower cost by partially replacing steel fibers with textiles,which is suitable to be used as a new light-weight and high-strength material for thin-walled structures facing in civil engineering.In this study,the mechanical properties of TR-UHPC and its potential in structural application were comprehensively studied by means of material preparation,constitutive relation and structural response.The pull-out tests were carried out to explore the bonding properties between textile and matrix in TR-UHPC.The mechanical properties of the composite were studied by direct tension and bending tests.The mechanism of tension stiffening and stress-strain constitutive relation were revealed considering the synergistic effects of hybrid fibers.The substitution relationship between steel fiber and textile was discussed and the theoretical model was proposed.Based on the material test and finite element simulation,the feasibility of using TRUHPC as strengthening materials was evaluated for structural members including reinforced concrete beam and column.The specific research contents and achievements are as follows:(1)Interfacial bond properties of TR-UHPC.The mechanical and geometric properties of carbon textile,glass textile and basalt textile used in the test are determined by the tensile tests of the three fiber textiles,among which the carbon textile showed the highest tensile strength and ductility.The interface bonding properties and bond slip constitutive relationships were obtained through the pull out test of textiles embedded in UHPC with different steel fiber content.Among the materials used,the basalt textile showed better interface bonding performance with UHPC matrix as the textile woven joints were more reliable.(2)Tensile behavior of TR-UHPC and the synergistic effects of fibers.The effects of different textiles,number of textile layers(textile reinforcement ratio)and short fiber content on the tensile properties of TR-UHPC were studied through the direct tension test.Carbon textile and short fiber exhibited good synergistic effect at low steel fiber content because of its high elastic modulus,while basalt and glass textiles tended to improve the mechanical properties of TR-UHPC at high steel fiber content.The optimal ductility of 4-layer carbon textile specimen was be obtained when the steel fiber content was about 1.0%,while the maximum ultimate strain of 6-layer was observed with steel fiber content of 0.5%,due to smaller layer spacing and worse dispersion of steel fiber.The optimal short fiber content of glass textile specimens was in the range of 1.5% to 2.0%,while that of basalt textile TR-UHPC specimens was around 1.5%.The tensile behavior of TR-UHPC was simulated by a one-dimensional finite difference numerical model considering the contributions of matrix cracking,short fiber bridging,textile tension and bonding.The contribution of steel fiber to tensile strength was further calculated based on the dispersion characteristics of short fiber in TR-UHPC.On this basis,the synergistic effects of fibers were explored and an approximately linear substitution relationship between steel fibers and textiles was observed.(3)Flexural behavior of TR-UHPC and inverse analysis to correlate the relationship between bending and tensile behavior.Four-point bending test of TR-UHPC was performed with different textile types,textile reinforcement ratio and short fiber content.It was found that the bending strength of three series of TR-UHPC increased approximately linearly with the increasing steel fiber content,but the ductility of carbon textile TR-UHPC showed opposite trend.By considering the energy absorption capacity up to the peak stress the optimal volume fraction of short fiber was in the range of 1.5% to 2.0% when the reinforcement ratio of carbon textile was 0.17%,and in the range of 0.5% to 1.0% when the reinforcement ratio was 0.25%.The highest performance was observed when short fiber was about 2.0% for glass textile with a reinforcement ratio of0.34%.When the distribution ratio of basalt textile was 0.41%,the optimal short fiber volume was between1.0% and 1.5%.The bending force-deflection curves of TR-UHPC were calculated by the parametric analytical model based on the tensile and compressive constitutive laws of materials.The tensile stress-strain curve was backcalculated from the bending test using the analytical model.The difference between the back-calculated and the test results and the different effects of textile position under tensile and bending were explored.The correlation between bending and tensile behavior of TR-UHPC was revealed.(4)Performance improvement of TR-UHPC strengthened structureThe mechanical responses of TR-UHPC strengthened structural members and the mechanisms of performance enhancement were studied by means of finite element analysis.Two case studies were presented including the axial compression behavior of column with precast TR-UHPC permanent formwork and the flexural behavior of TR-UHPC strengthened beams.With the increase of the number of textile layers,TRUHPC formwork significantly improved the bearing capacity and ductility of column.TR-UHPC reinforcement layer can significantly improve the overall stiffness,yield load and peak load of the strengthened beam.The improvement in bearing capacity was limited when there were only short fibers and the strain softening behavior governed.The pronounced strain hardening behavior of TR-UHPC reinforcement layer at higher tensile strains can significantly improve the bearing capacity of the structure,which can be achieved at lower content of steel fibers. |
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