Research On Impact Resistance Of Steel Fiber-steel Reinforced High Performance Concrete

High strength concrete with obvious brittleness, steel fiber can significantly improve the toughness of concrete and energy absorption capacity, effectively inhibit the formation and expansion of concrete cracks. It can meet the performance of high durability, crack resistance, resistance fatigue etc which ordinary concrete can not meet for pre-cast piles and other special components under the impact load.The new developed drop-weight testing equipment has been fabricated and set up based on the drop-weight impact test recommended by ACI committee 544. The hammer can be precision fixed and the height of the drop hammer can be controlled strictly by positioning magnetic switch. Also the magnetic switch can ensure that the initial velocity of the hammer is zero, avoid the inaccuracy result from manual operation and ensure the specimen can bear the same impact energy at each impact; the protection device is offered to reduce the energy loss and ensure the safety at impact; the baseplate should be bolted to a rigid base, such as a concrete floor or cast concrete block to reduce the energy loss at impact. The investigation on the impact properties of plain concrete, RC specimens, SFC specimens and RC+SFC specimens with different steel fiber dosages has been carried out.Results show that steel fiber can effectively improve the impact resistance, decrease the brittleness of the concrete and delay the formation and development of impact crack. With the increasing of the fiber content, the crack width of the specimens is decreased and the energy absorption of the specimens is improved at the first crack; the crack number are increased and the energy absorption of the specimens is greatly enhanced at ultimate failure. The combination of steel fiber and steel rebar shows significant positive composite effect on the impact resistance, and the toughness of the specimens is greatly improved. In addition, using the data collection system of Synergy, the acceleration response of all specimens at different impact step are collected, frequency-domain analysis of impact is carried out with FFT of acceleration response. Resilts show that the value of frequency of the specimen are decreased at the biggest acceleration with the enhance of the damage level of the specimen.