Evolution of energy dissipation during four-point bending of bituminous mixtures

In this investigation, the fatigue life of bituminous mixtures is characterised using the four-point bending test. Two sets of bituminous concrete samples, one produced with unmodified binder and other with plastomer-modified binder, are subjected to repeated strain-controlled sinusoidal loading at 10 Hz frequency and 20°C. The test is conducted for three different strain amplitudes of 200, 400 and 600 microstrain and the corresponding stress and strain data are collected at 1/1000 second interval. In the first approach, these data are used to calculate total energy dissipation. The dissipation due to damage is determined by separating viscoelastic dissipation from the total dissipation. For this purpose, a linear viscoelastic model is used. In the second approach, the discontinuity in the evolution of phase lag determined from the stress–strain plot is taken as the onset of fatigue damage. The fatigue failure, as quantified by these two approaches, was found to be closer to the fatigue life computed using energy ratio method.