Asphalt concrete (AC) is a composite material that exhibits time and temperature-dependent properties, and it is generally accepted that AC behaves as a linear viscoelastic solid at small strain levels. Nevertheless, different mechanisms and the damage evolution can change its behaviour from the linear viscoelasticity. This study was focused on identifying the causes of the deviation of AC viscoelastic properties under different loading conditions and at small strain levels during complex modulus tests. Sinusoidal tension–compression and compression tests on six asphalt mixtures produced with the same aggregate gradation but different asphalt binders under stress- and strain-controlled conditions were performed within a defined range of frequencies and temperatures. It was found that aggregate interaction and energy dissipation characteristics were the main mechanisms that influenced deviations in the viscoelastic properties, but they were only significant at high temperatures and during considerable nonrecoverable accumulated deformation.

Key words: Asphalt concrete, complex modulus, hysteresis loop, aggregate interaction, energy dissipation