Experimental Research On Impact Resistance Of Fibre Reinforced Concrete

Resistance to impact load is recognized today as one of the important properties of concrete used for structural applications. Some studies have shown that the addition of fibres has remarkably positive effect on the impact resistance of concrete to dynamic force. At present, the most building structures and infrastructures are made of steel reinforced concrete, but, the study on the hybrid effect of steel fibre and steel rebar on the impact resistance of concrete is very limited at home and abroad.The drop-weight test method recommended by the ACI Committee 544 is regarded as the simplest and has been used widely in the study on the impact resistance of concrete. In order to reduce the scatter of impact results caused by artificial operation, a new drop-weight test device based on the ACI recommendation was fabricated. With the help of new test device, the concrete specimens were impacted at the same point by the freely falling of drop hammer from the same height, so that the boundary conditions of each impact were kept evenly in this test. The investigation on the impact properties of NC specimens, RC specimens, PPFRC specimens, SFRC specimens and RC+SFRC specimens with different fibre dosages has been carried out.Results show that addition of fibre 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 fibre content, the crack width of specimens is decreased and the number of crack is increased at failure, and the stress distribution in concrete matrix is more uniformly. Moreover, the combination of steel fibre and steel rebar demonstrated a significant positive composite effect on the impact resistance, which results on the improvement in impact toughness of concrete specimens. In view of the variation of impact test results, the two-parameter Weibull distribution was adopted to analyze the experimental data. It was proved that the probabilistic distribution of the blows to first crack and to final failure of all types of samples were approximately two-parameter Weibull distribution. Lastly the impact resistance formulae for PPSFC with different fibres dosage are developed to facilitate the application.