Flexural Properties of Ultra-high Performance Concrete Under Fiber Synergistic Effect

Abstract:

To study the effect of steel-polypropylene crude fiber on the bending and tensile properties of ultra-high performance concrete （UHPC）， a four-point bending test was conducted to obtain different volume contents （the content of steel fiber and polypropylene crude fiber being 0， 0.5%， 1.0%， and 1.5%）. The load-deflection curve under the combination is described from the failure form， flexural strength， flexural toughness， etc.， of the specimen， and a model with high feasibility is derived from the fitting formula of the single-doped fiber to analyze the synergistic effect of the hybrid fiber. Finally， the microstructure of the hybrid fiber UHPC was observed and analyzed by scanning electron microscopy （SEM）. The test results show that the incorporation of steel-polypropylene crude fiber significantly improves the flexural strength of UHPC， with an increase range of 17.8% to 101.2%. At the same time， using the proposed method， it is found that the synergistic effect of hybrid fibers showed a positive synergistic effect when the total fiber volume content is between 1.5% and 2.0%， and the best positive synergistic effect is obtained in S10P10. In addition， compared with the specimens without fiber， the initial crack toughness of matrix specimens increases by 51.8 % to 98.2 % and 33.9 % to 48.2 % respectively with the addition of steel fiber and polypropylene crude fiber. When the content of steel fiber is 1.0% and the volume content of polypropylene crude fiber is 1.0%， the improvement to the bending toughness of UHPC is the best， which further verifies the evaluation model of fiber synergy effect. Finally， the synergistic effect and the toughening mechanism of the hybrid fiber are revealed at the micro level.