Effect Of Fibers On The Toughness And Flexural Impact Resistance Of Concrete

During the service stage, concrete structure may subject to high strain rate impact load, especially bending impact. With the improvement of toughness, tensile strength, cracking resistance, fiber reinforced concrete has been applied more and more widely. Domestic and foreign studies have shown that fiber, especially steel fiber, can significantly improve the impact resistance of concrete. In order to enhance the impact resistance of structure with fiber reinforced concrete, there are still many problems to be solved with further research and exploration. In this paper, experimental researches on the flexural impact performance of steel fiber reinforced concrete beams and steel fiber reinforced concrete beams with conventional reinforcement have been conducted. And the impact resistance of steel fiber reinforced expansive concrete(SFE) was investigated according to the guideline of ACI544. Besides, the mechanical property and durability of SFE have been investigated.Starting from the request of flexural impact test, summarizing the technique characteristics of existing impact devices, a new drop-weight flexural impact test device was fabricated. We can get more accurate results and test various specimens with different sizes by using this new device, and it is well suited to the repeated impact test. A series of flexural impact tests has been conducted on this new device, and results indicated that, the addition of steel fibers significantly improved the flexural impact resistance of concrete and the improvements increased with the fiber content. Rebar seemed to behave much better than do steel fibers under bending impact. The improvement of flexural impact resistance showed in steel fiber reinforced concrete beams along with conventional reinforcement exceeded the superposition between steel fibers and rebar, in other words, the combination of steel fibers and steel rebar demonstrated a significant positive composite effect. With high fiber content (50kg/m3), expansive agent had a positive effect on the flexural impact resistance, but it was not obvious when fiber content was relatively low. It is intuitive to compare the flexural impact resistance under different fiber contents by using the statistical model. Stiffness of the specimen increased with the fiber content, also the contact force. Lower contact force was observed during the second blow due to the internal damage caused by the first strike, and the impact process took longer time.According to the experimental researches on the mechanical property and durability of SFE, under the combinative effect of steel fiber and expansive agent, the mechanical properties of concrete are significantly promoted, and the toughness is greatly improved. SFE showed the best volume stability, in addition, the best adhesive performance has been achieved between SFE and old concrete. Three kinds of concrete, following designed mix proportion, all showed good durability.