Papers by Author: Qing Xin Zhao

Abstract: After being subjected to different elevated temperatures, ranging between 200 °C and 800 °C, the flexural strength, matrix mass loss rate and water absorption of polypropylene (PP) macro-fiber reinforced high strength concrete (HSC) were investigated. Moreover, the internal damage of concrete was analyzed by the ultrasonic non-destructive testing technology. The results indicate that PP macro-fiber in HSC has an adverse effect on flexural strength, while the synergistic effect of hybrid fibers (PP micro-fiber plus PP macro-fiber) can minimize this effect. Compared with PP micro-fiber, PP macro-fiber is more effective in increasing the matrix mass loss rate and water absorption of HSC. However, if the dosage of PP macro-fiber is too high, the pressure relief channels formed by fibers melt will be too coarse, and the total porosity of HSC will be increased significantly. Finally, a mathematical model relating the damage degree to temperature was established based on the non-linear fitting of the experimental data.

Abstract: By means of the three-point bending impact equipment, with the measurement of ultrasonic velocity, the low velocity impact damage evolution of reactive powder concrete (RPC) with 0, 1%, 2% and 3% volume fraction of steel fiber were tested. In this study, the damage variable D pertaining to ultrasonic velocity had been selected to study the damage evolution process of RPC. The results indicate that the fatigue damage process of RPC is linear. The addition of fibers effectively improves the impact energy absorption behavior of RPC matrix, and the damage variable D of RPC with different fiber dosages increases by 1.1~3.5 times than that of plain concrete when it is ultimately destroyed.

Abstract: By means of the three-point bending impact equipment, with the measurement of ultrasonic velocity, the impact behavior and damage evolution of reactive powder concrete (RPC) with 0, 1%, 2% and 3% volume fraction of steel fiber were tested. The results showed that steel fiber significantly improved the compressive strength, flexural strength, flexural toughness and impact toughness of RPC matrix. The compressive strength, flexural strength, flexural toughness of RPC with 3% steel fiber increased by 40.1%, 102.1%, and 37.4 times than that of plain concrete, respectively, and simultaneously, the impact toughness of RPC with 3% steel fiber was 93.2 times higher than that with 1% steel fiber. RPC with 2% and 3% steel fiber dosage both had relatively high compressive strength, flexural strength and flexural toughness; however, compared with the sample with 2% steel fiber dosage, the impact toughness of RPC with 3% steel fiber dosage increased by more than 10 times. Therefore, taking economy and applicability into consideration, if we mainly emphasis on the compressive strength, flexural strength and flexural toughness, RPC with 2% steel fiber is optimal. While if impact toughness is critical, RPC with 3% steel fiber would be the best choice.