Evaluation of the effect of deflection waveform on fatigue performance of asphalt mixture in the four point bending beam test

Abstract

An experimental study was conducted to determine the effect of deflection waveform on four-point flexural fatigue test results for hot mix asphalt. This paper reports how the waveform affects the fatigue resistance of an asphalt mixture and, consequently, the fatigue models of the material. The mix was tested at different strain levels under both haversine and sinusoidal deflection-controlled modes. The findings indicate that haversine displacement control testing results in a sinusoidal strain response of half the intended amplitude. This outcome was attributed to the viscoelastic nature of asphalt mixes. In the deflection controlled haversine test, permanent deformations lead to a new equilibrium neutral position of the beam and the force output follows a sinusoidal waveform. This produces erroneous fatigue results since the test assumptions do not match the actual test conditions. It is recommended to use a sinusoidal waveform to obtain consistent results.