IMPACT STRENGTH OF FRC MATERIALS

The paper describes toughness measurements carried out on polypropylene and steel fibre reinforced concrete mixes using both quasistatic tests and impact tests. Both types of test were carried out on identical notched fibrous beams subjected to three-point bending. The quasistatic toughness measurements were evaluated by means of two toughness indices (based on ratio of areas under the load-deflection graphs) together with the total energy required to achieve complete failure of the test specimens. The impact toughness was evaluated from the number of blows required to completely fracture the test specimens which was then converted into energy. The impact apparatus was instrumented by two load cells to monitor the impacting loads and the corresponding loads at one of the supports. The load cells were connected to a Signal Memory Recorder which gave load-time curves for the impact events. The load-time graphs showed the greater efficiency of heavier masses in producing impact failure in the specimens. The impact apparatus is versatile and can be used to study a range of variables including impacting mass, drop-height, beam span and notch depth. The overall pattern of results showing the enhanced toughness with increasing fibre concentration was the same in the two methods of testing. A comparison between the quasistatic and impact test results shows that twice as much energy is absorbed in the impact tests as is absorbed in the quasistatic tests. Further work is recommended in this area to determine the relative magnitudes of the various energies lost during the impact event. © 1990.