FATIGUE PERFORMANCE IN FLEXURE OF FIBER-REINFORCED CONCRETE

An experimental investigation of the behaviour of fiber reinforced con crete under cyclic flexural loading is presented. One type of polystyr ene and two types of steel fibers in two different volume concentratio ns are studied. Load-deflection response is obtained for constant ampl itude fatigue loading as well as for static loading. The damage level is recorded under static and fatigue loading using acoustic emission t echniques. Data is presented in terms of complete load-deflection diag rams (for static loading) and in terms of S-N diagrams (for fatigue lo ading). Damage evolution is described in terms of acoustic emission ac tivity as a function of deflection (static loading) or cycles (fatigue loading). The test results show that the addition of steel fibers inc reases the flexural fatigue strength considerably. Compared with plain concrete the fatigue strength for 2 million cycles is changed from 60 percent to 90 percent of the ultimate flexure strength when the steel fiber content is 1 volume percent. High fiber volume concentrations ( 2 percent) further increase absolute fatigue strength; however, fatigu e performance measured relative to the static strength is decreases co mpared to the lower fiber volume concentration. Furthermore, the resul ts show that the accumulated damage level at failure in the static tes t of reinforced concrete is of the same order of magnitude as in the f atigue testing of the same material. However, using fiber reinforced c oncrete the accumulated damage level in fatigue testing is 1 - 2 order of magnitude higher than the level reached in static testing of the s ame material. Finally, the tests show that the deflection at failure o d the fiber reinforced concrete specimens under constant stress range fatigue loading can be predicted using the static load-deflection curv e, provided the testing time is short enough to neglect creep effects.