Temperature wave fatigue damage and dissipated energy approach to flow number estimation of asphalt concrete

The effect of sinusoidal temperature on the fatigue life of asphalt concrete (AC) under continuous loading was investigated. The traditional failure criteria of 50 % loss in stiffness, stiffness ratio, and dissipated energy ratio were employed to analyze the AC fatigue test results. Dissipated energy approach and dissipated energy ratio were also extended to estimate the flow number (FN) of AC. The varying temperature induces a continuously changing temperature gradient across the AC beam. This, in turn, triggers the formation of continuously alternating weaker and harder outer layer relative to the beam core, thus creating a stiffness undulation. The combined effect of the load and temperature cycles resulted in a stiffness diminishing trend similar to that of damped harmonic vibration energy. The bottom of the beam is subjected to additional tensile strain/stress for a negative temperature gradient, while the top of the AC beam is subjected to additional compressive strain/stress for a positive temperature gradient. The temperature amplitude and period have a significant influence on the diminishing trend of the stiffness. Results from all the fatigue life estimation and prediction methods employed showed that the fatigue life of AC under variable temperature is shorter than that under constant temperature. However, the effect of the variable temperature is felt much more at lower strain loading. Nonrecovered strain energy method was successfully employed to estimate the AC FN.