Flexural Behaviour of Carbon Textile-Reinforced Concrete with Prestress and Steel Fibres
Four-point bending tests were adopted to investigate the influences of the number of textile layers, volume content of steel fibres, and prestress on the flexural behaviour of carbon textile-reinforced concrete (TRC). The failure mode of the specimen changed from debonding failure to shear failure, accompanied by the matrix-textile interfacial debonding with an increasing number of textile layers. The interfacial bonding performance between the textile and matrix improved with the addition of steel fibres in the TRC specimens. The presence of prestress or steel fibres improved first-crack and ultimate stresses of the TRC specimen. In comparison with the first-crack stress, a more pronounced enhancement in the ultimate stress was achieved by the addition of steel fibres. However, the effect of prestress on the first-crack stress was found to be more significant than on the ultimate stress. The prestress combined with steel fibres further improved the flexural behaviour of the TRC specimens. The prestressed TRC specimens with 1% volume content of steel fibres effectively avoided debonding. Thus, the utilization of the textiles could be improved.
Glass Concrete Thin Sheets Prestressed with Aramid Fiber Mesh
Concrete has been prestressed traditionally with high-strength steel. The vulnerability of such material to corrosion calls for alternate materials, if thin-sheet products are to be prestressed. A research project at Columbia University is investigating the feasibility of using aramid fiber mesh for such purpose. This paper explores the chemical and mechanical properties of aramid in the form of both individual fibers and rovings. Although the material is inherently brittle, its high strength and stiffness appear to make it a suitable medium for prestress applications. Appropriate pre-stretching of the mesh can minimize prestress losses due to relaxation. The low bond strength requires special measures for both stressing and anchoring of the mesh. Also the chemical interaction between the fibers and the cement matrix calls for attention. Because of the potential of crushed glass aggregate for decorative and architectural thin-sheet applications, pilot studies have been performed using glass concrete matrices.
Bond Behavior of Textile Reinforcements - Development of a Pull-Out Test and Modeling of the Respective Bond versus Slip Relation
For strengthening existing concrete structures with textile reinforced concrete (TRC), anchoring of the TRC layer to the old concrete is crucial. Owing to their very high tensile strength, especially the anchorage lengths of textiles consisting of carbon fibers are to be determined from the pull-out of the filament yarns of the fine-grained concrete. For this reason, further research was necessary to clarify the failure criteria caused by yarn pull-out, which necessitated the development of a pull-out test for textile reinforcements. With the help of the force-crack opening relationships determined within these experimental investigations, the respective bond stress versus the slip relationship (BSR) of the textile reinforcement could be modeled analytically.